A “no start” means the engine won’t start when you turn the key or press the button. The episode is about a less-common reason: the exhaust being blocked so badly the engine can’t run.
“Restricted exhaust” means something in the exhaust system is partially blocked. If it’s blocked badly enough, the engine may not be able to start because the exhaust gases can’t get out.
This sounds like the catalytic converter (the emissions part in the exhaust). If it gets clogged or fails, it can choke the exhaust flow—leading to weak power, rough running, and sometimes the engine won’t start.
Misfires are when one or more cylinders don’t burn fuel correctly. The engine can feel rough and lose power, and it may happen when the engine is struggling due to issues like exhaust restriction.
In troubleshooting, “eliminating everything else” means you test the most common possibilities first and cross them off. Then you’re left with fewer options that you can check more carefully.
Instead of trusting one clue, diagnostics often uses several test results together. When multiple symptoms all point in the same direction, it’s much more likely you’ve found the real problem.
An O2 sensor is a small sensor in the exhaust that helps the car figure out the fuel/air mix. In some diagnostics, people remove it to see if the engine starts when exhaust flow is changed. On older cars, it can be hard to remove because rust can seize it in place.
An oxy-acetylene torch is a tool that uses very hot flame to loosen stuck metal parts. People use it on rusted exhaust components so they can get them out. But too much heat or force can still damage the sensor or its threads.
A catalytic converter is a part in the exhaust that helps clean up the car’s emissions. If it gets clogged, it can block exhaust flow and cause starting/running problems. The host mentions it because it’s a common place where exhaust restriction can happen.
The 2002 Honda Odyssey is a minivan from the early 2000s. Here it’s the example car that wouldn’t start reliably, so the host walks through how to narrow down why.
Term
airfield spark
This sounds like the host is talking about the basics needed to start an engine: air, fuel, and spark. If one of those is missing, the engine may crank but won’t run.
Compression is the engine’s ability to squeeze the air/fuel mixture inside the cylinder. If it can’t build enough pressure, the engine may not start or may stall right away.
Anti-theft is the car’s security system that can stop the engine from running. Sometimes it lets the car start for a second, then shuts it off if it doesn’t recognize the key.
The Toyota Camry is a common family sedan. Here it’s mentioned because the speaker thought the car’s security system was causing a start-then-stall problem.
The Ford Explorer is a well-known SUV. In this story, it’s mentioned because it had a similar start-and-then-stall behavior that the speaker first suspected was caused by anti-theft.
A “start stall” is when the engine starts for a moment and then dies right away. The way it behaves over repeated attempts can help narrow down why it won’t keep running.
“Immobilized” means the car’s security system is blocking the engine from starting. The dashboard may show an immobilizer warning, and the computer may stop fuel from being injected.
Injector pulse width is how long the fuel injector is told to spray. Longer pulse width usually means more fuel; if it stops, the engine can’t get enough fuel to run.
“Flooded out with fuel” means there’s too much fuel in the engine. If there isn’t enough air to burn it, the engine can’t start and may keep failing after more cranking.
Combustion needs oxygen from the air. If the engine can’t pull in fresh air, it can’t burn the fuel, so you get no combustion.
Term
mobilizer codes
This sounds like the car’s anti-theft system codes. If the immobilizer doesn’t recognize the key (or detects a fault), it can stop the engine from starting.
A spark plug is the ignition component that creates the spark needed to ignite the air-fuel mixture in each cylinder. Inspecting a spark plug can reveal whether fuel is reaching the cylinder (e.g., a wet plug suggests flooding or misfueling).
A plugged up exhaust means something is blocking the exhaust pipe or muffler area. If the gases can’t get out, the engine may struggle to start—and it can confuse what the compression test shows.
Cylinder walls are the inside surfaces of the engine cylinders. If fuel washes over them, it can change how the engine seals and can make compression readings look worse than the true mechanical condition.
A “bank” is a group of cylinders on one side of the engine. If one bank seems to have low compression, it can point you toward a problem—but the host says that in this case it wasn’t the real cause.
Extended cranking is when the starter keeps turning the engine for a long time but the engine won’t catch. It’s a clue that something is preventing the engine from actually starting, like fuel not igniting or fuel getting into the wrong place.
A spark check is testing whether the ignition system is actually firing a spark at the spark plug. If there’s no spark, the engine can’t ignite the fuel, even if fuel is present.
A fuel sample means taking a small amount of fuel and checking it. The goal is to see if the fuel is the right type and in good condition, because bad or contaminated fuel can prevent starting.
The ECM is the engine computer that decides how much fuel to send to the engine. If you put in the wrong kind of fuel, the computer may not be able to adjust enough to make the engine start normally.
Term
85
“85” usually means E85, a fuel that’s mostly alcohol (ethanol). If the car expects E85 but you put in a different gasoline blend, the engine computer may not inject the right amount of fuel to start.
A fuel quality sample means checking what kind of fuel is really in the tank. If the fuel blend is different than what the car expects, the engine may not start or may run poorly.
E10 is a common gasoline blend that has about 10% alcohol (ethanol) mixed in. If the car’s computer expects a different blend than what’s in the tank, it can cause a no-start condition.
Ethanol is the alcohol part of many gas blends. Since it burns differently than regular gasoline, the car’s computer may need to inject more or less fuel depending on how much ethanol is in the tank.
The coolant temperature sensor tells the computer how hot the engine is. If it lies (reads wrong), the computer may add too much or too little fuel and the car may not start.
Key on engine off means the ignition is on, but the engine isn’t running. It’s a good time to check sensor readings because they should make sense even before you start the car.
A rationality check means you compare sensor readings to see if they “make sense” together. If they don’t, something is likely wrong with a sensor or its signal.
The mass airflow sensor tells the computer how much air is going into the engine. If it’s wrong, the computer may add the wrong fuel amount and the car may not start.
Unplugging the mass airflow sensor is a quick test to see if the car changes behavior. If it helps, that’s a clue the sensor (or its signal) is causing the problem.
A “dynamic” sensor changes its behavior as the engine’s conditions change. So it might work fine sometimes, but give wrong readings at certain speeds or loads.
A cam sensor (camshaft position sensor) tells the engine computer where the camshaft is in its rotation. If a bank doesn’t have a cam sensor, the computer may not be able to detect or code cam-related timing faults for that bank.
Exhaust valves are the valves that open so the engine can push out exhaust gases. When they open, pressure inside the cylinder and the exhaust system changes. The diagnostic trace they’re discussing is tied to that event.
The exhaust manifold is the engine’s “collection pipe” for exhaust gases. It gathers fumes from the cylinders and sends them down the exhaust system. If it’s affected by a blockage, you can see unusual pressure behavior.
Vacuum here means the engine is sucking air through the intake. If you don’t see the expected suction while cranking, something may be preventing airflow.
The MAP sensor tells the car’s computer how much pressure is in the intake. If it shows the engine isn’t pulling vacuum like it should, that’s a clue something is blocking airflow and the engine can’t run.
EGR is a system that sends some exhaust back into the engine to reduce emissions. If the EGR is stuck open, it can mess up the air/fuel mixture enough that the engine won’t start—so disconnecting it can be a useful test.
This is a 2007 Ford Mustang example the host uses to explain a troubleshooting trick. They say disconnecting the EGR can help the engine start if the EGR is causing the intake to be “choked.”
The host brings up a Chevrolet Silverado as another example from their diagnostic work. It’s part of the same discussion about figuring out why an engine won’t start or keeps stalling.
Term
Frank Nostar cylinders
The transcript mentions “Frank Nostar cylinders,” but it doesn’t match a common car term. It sounds like the host is referring to something specific about the engine’s cylinders, but the exact meaning isn’t clear from the wording.
Term
WPS
WPS sounds like a specific diagnostic step or tool the host uses to check a no-start problem early. The takeaway is that using it first can help you find the issue faster instead of guessing after other checks.
Term
O2
O2 usually means the oxygen sensor. It tells the car’s computer how much oxygen is in the exhaust so it can adjust the fuel mixture; if it’s acting up, the engine may not run correctly.
A Y pipe is the part of the exhaust where two pipes join into one. Where that join happens affects how the oxygen sensors “see” what’s going on in the exhaust.
Upstream converters are catalytic converters closer to the engine. If one gets clogged, it can restrict exhaust flow and make the engine struggle to start.
A V8 is an engine with eight cylinders arranged in a V shape. It’s a common layout in many trucks and performance cars, and it changes how the engine fits and sounds.
Term
exhaust plateau
An exhaust plateau is a part of the test where the exhaust reading levels off for a moment. That pattern can help a technician judge what’s happening in the exhaust system.
The four-stroke cycle is the basic engine rhythm: intake, compression, power, and exhaust. Diagnostics use it to figure out whether the engine’s timing events line up correctly.
A phaser pin is part of a variable valve timing (VVT) system that helps control the cam phaser’s position. If it sticks, the cam timing can become incorrect, which can prevent the engine from starting.
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Welcome to the Automotive Diagnostic Podcast.
We're going to explore ways to sharpen our diagnostic skills, find learning resources,
and hear from experts in the automotive field.
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Hey, what's going on?
Automotive World.
Welcome to another episode of the Automotive Diagnostic Podcast.
My name is Sean Tipping.
I'll be your host once again for this week's episode.
Thank you so much for joining me today on the show.
It's just me and I've got another case study or a couple case studies here for you.
It's a little bit of a theme.
This is something that I've ran into, I don't know, a handful of times, maybe eight or nine
times over the course of doing mobile, a few more, just as a technician.
It definitely doesn't happen all of the time.
And sometimes it presents itself in a different way.
And in that case, I've seen it a lot more.
But what it causes is a no start for the vehicle.
But the reason of the no start, it's just not the most likely scenario or not the first
thing that at least I think of when I hop into a no start vehicle.
So I'll just spill the beans here.
What I'm talking about is restricted exhaust.
Now, like I mentioned, if we're just talking restricted exhaust, where it causes a performance
issue, right, most of the time that's low power, I've seen this probably hundreds of
times, right, that be Cadillac converter, whatever is restricting the exhaust.
Usually it is a converter, you know, even if it's one that broke down and went into
the other one, it will cause a situation where you can still start your engine, it'll still
run, it'll idle, and maybe even accelerate somewhat, but you either have severely reduced
power, maybe you have misfires on one side of the engine, be some symptoms, but you can
still actually start the engine and run.
Now, you have an exhaust that is so restricted that you can't even start the engine.
That's a little bit of a different story.
Now, it does happen.
You've probably ran into it out there.
Maybe you haven't.
You know, maybe you have not seen that, seen vehicles, but when it comes about, it's
definitely thrown myself and members of my team for a little bit of a loop before we
got there.
Now, the reason I'm talking about it is number one, kind of an interesting reason for an
engine to not start.
And we can talk about some of the symptoms and the way that you could catch this, eliminating
everything else, which the first time I ran into this was the case.
I just eliminated everything else.
And I'm like, well, okay, I have to go this route.
And it ended up being the restricted exhaust, but we saw it twice in one week, which I
thought was odd just again, because it doesn't happen every day where you have a no
start from a completely plugged up or restricted exhaust.
Okay.
So I'll talk about those cars and then a couple other ones over the years so that I
can group together some tests, some symptoms and some things that you can use to kind of
catch and say, oh, okay, this is, you know, leading me towards a potential restricted
exhaust.
Now, of course, some of the symptoms might match up with some other reasons that engine
might be a no start.
Again, a lot of times in diagnostics, we're adding up a number of different tests and
symptoms to point to one thing.
And if you have enough of them that all points to the same thing, okay, let's go, you
know, check that out.
Now, we can do some of these tests to really help prove that it is in fact the exhaust,
but the visual to actually make sure that is the part there, that is the component that
is keeping the engine from starting.
It's a little bit tougher because you have to take apart the exhaust in some form.
Now, maybe you live in a state down south where pulling out O2 sensors is not an issue.
And hopefully they're easy to get to.
For me, that is almost never a realistic possibility.
Number one, because I don't always have access to underneath the vehicle easily.
We, yeah, could we get it into a shop and up on a horse potentially?
But then I got to use somebody else's tools to get the O2 sensor out.
I don't carry that stuff with me.
But I also live in the rust belt where there's a lot of salt on the road.
And if that vehicle is, I don't know, older than 67 years old, there's a real
good chance I'm going to need an oxy acetylene torch to get that oxygen sensor out.
And when I do, I might damage the threads or the sensor itself in order to get it out.
And so you don't want to make it something where you're damaging a sensor just to try
to prove it. Now, if you could do that easily, that's one of the simplest things you can do
is yank the O2 sensor out and then try to start the vehicle.
And if it starts and runs with the O2 sensor out and you'll hear it,
there'll be a lot of pressure coming through that hole.
Then, you know, that's a really good sign that, hey, OK, we have, you know,
a restricted exhaust here.
Back in the day, I remember I worked with somebody who he would test for
a restricted exhaust on a running engine by drilling a small hole in front
and behind the catalytic converter.
And you could measure the pressure on each side or you could just listen and feel it.
And it would be a pretty obvious sign.
Now, I don't know how well that's going to work for you in a no start scenario.
And I think we have some better tests for measuring pressure nowadays.
But this was a long time ago, and that was how this guy did it.
But anyways, pulling that O2 sensor out, if possible,
and this, of course, would have to be ahead of the restriction and the exhaust.
That would do it. OK.
But again, not a realistic test for me to do in most situations,
most of the cars I'm working on.
So I have to, you know, do some other things to get there.
And I have to get to that point, you know, just in general,
that I think this is a restricted exhaust.
There have to be something pointing me in that direction. OK.
So I'll give you the first vehicle that I was working on here
just a couple of weeks ago was a 2002 Honda Odyssey.
And this vehicle had been sitting for a while and it didn't want to start.
Or it would start just like real briefly and then it would stall out.
And then it would just crank and maybe pop every once in a while here.
But it wouldn't start again.
And we went through.
And of course, we're checking our basics here of, you know, airfield spark.
What do we have? What's missing?
Where is the problem here?
Also, when I say air, looking at the compression of the engine.
And there's a couple of things here in your initial inspections on a vehicle
that might at least add restricted exhaust to the possibilities.
One of the things that I notice with these vehicles is at least
after they've been sitting for a period of time and by period of time,
an hour or more.
And this also would depend on the ambient temperature
that could increase the wait time.
But it's enough time for any built up fuel in the cylinders
to maybe evaporate so that they're not completely flooded or washed out.
And at this point, when you go to start the vehicle,
it will actually start briefly and then it will shut off.
And this could also lead you towards an anti theft situation.
And I had a Toyota Camry years ago where I thought it was an anti theft
situation because it would kind of do like a start stall thing.
I had I actually had a Ford Explorer years back, too,
that had a similar restricted exhaust, thought it was an anti theft thing.
But that was the situation where it would kind of start, then it would stall.
And what's happening there is after the vehicle has been sitting for a while,
the fuels dried up in the cylinders, you go to start it and you have everything
you need immediately, right?
You have fresh air coming into the engine, you've got spark,
you've got fuel spraying, you've got the correct compression.
And for a very brief period of time, the four stroke cycle is able to happen.
But as soon as that exhaust fills up because we can't push anything out,
then that exhaust is going to work its way back into the engine.
Once that exhaust valve is open, we can't really push anything out.
So we can't draw anything, any fresh air.
And then we can't do the four stroke cycle anymore.
So you get out of that a kind of start stall.
So it could be pointing towards an anti theft.
Now, we have other ways to determine is this an anti theft problem or not?
Of course, that depends on the car, how obvious it's going to be.
But usually there's something that's going to point towards, you know,
what this car is immobilized, whether it's a light, it's a code,
it's a data pit, or just the fact that, hey,
the computer is shutting off the injectors shortly after this thing starts.
And in this case, you wouldn't have any of that, right?
You're not going to have any immobilizer codes.
You're not going to have any immobilizer light because it's not immobilized.
And the injector pulse width is not going to stop.
Okay. Now here's the other thing.
And this was the case on the couple of vehicles that I worked on over the last
couple of weeks. I can't say this is 100 percent true across the board.
But I would get that start stall immediately, or at least maybe in like the
first couple of attempts.
And then after that, it basically became a crank no start,
meaning that it is no longer starting.
And this is from what I can tell the engine actually getting
flooded out with fuel, because we're not able to bring in any fresh oxygen.
We're not able to have any combustion in that cylinder.
And we're just adding more and more fuel as we go.
And this can cause something else that I'll bring up that might be a sign that,
Hey, this is what we're dealing with.
But that's the initial scenario getting into these where you might observe
like, okay, this is like a crank start stall at first.
And then it turns into just a no crank or I'm sorry, a crank, no start.
And I don't have any, you know, a mobilizer codes or anything like that.
Now, the other thing that I notice on in this exact situation is if you're to
take a spark plug out to inspect in the cylinder, number one,
the spark plug is going to be wet with fuel.
And you may even have a buildup of fuel in the cylinder.
Now, this can lead to another thing that can be misleading, but it goes along
with the symptoms that I've seen on these engines.
And I've seen this multiple times in this scenario where a plugged up
exhaust keeps it from starting is you will have low compression on one or more cylinders,
but maybe not all of them.
And again, the reason the fuel getting dumped into these cylinders as you're
as someone is attempting to start it, maybe it's you, maybe it's the person
before you actually washes down the cylinder walls to the point where it drops
the compression on one or more cylinders.
And again, I've seen this as a repeatable symptom of these exact scenarios.
And it is a bit misleading, specifically with Odyssey that we looked at
because it made it look like one whole bank was low on compression compared to the other.
And while maybe that was true, that the actual compression wasn't the reason
that the engine wasn't starting.
It was a restricted exhaust, but the restricted exhaust causing the no start
caused an extended cranking on this thing caused too much fuel to wash
down the cylinders and drop the compression down.
Now, anytime we're looking at a cylinder that has low compression,
especially if you're looking at it like relative compression, which I would be
doing here, you may want to add a little bit of oil, if it's possible,
to that cylinder to see if it bumps the compression back up.
And that's much easier said than done, especially if you're in the field doing
it mobile, but, you know, it's the difference between calling an engine
and, you know, actually calling what is actually wrong with the vehicle.
So something to think about there, but that's what I see happen.
Now, the cylinders being flooded with fuel, the spark plug being wet with fuel,
we could do our spark check and make sure that we're actually getting spark
in that case, you should at least be able to say, yes, something is being
sprayed into the cylinders.
The correct fuel is going to be a possibility here.
And I have seen scenarios where vehicles will exhibit the same symptoms,
whether it be a crank start stall or just a brake no start from improper
or contaminated fuel.
And so this is a good time that you may want to do a fuel sample to see, well,
not only what the pressure is, but then also what's the quality of the fuel
that's going in here, right?
There are situations and ambient temperatures that could cause just
this something as simple as 85 being put in a vehicle that's not meant for it.
Even an 85 vehicle that has the internal ECM's calculation for fuel delivery off,
you know, it basically, it thinks it's the 85, but it's not or vice versa.
That could cause a no start.
So you want to do a fuel quality sample, not only to look at, okay,
is it actual gasoline?
If it's a gasoline engine, that's what I'm talking about here.
Is it 85?
If it expects the 85, is it just regular, you know, E 10 pump gas?
If that's what it expects, you'll have to look at the vehicle that you're
working on and how to determine, you know, is it in the 85 vehicle?
And what is it expecting right now per the PCM, right?
What pulse width for the injectors is it actually running on the percentage
of ethanol it thinks is in the fuel?
This episode is brought to you by L one automotive training and Keith Perkins.
If you're looking for education on module programming, J 25 34 E
prom work, key in a mobilizer, electrical diagnostics or drivability diagnostics.
Keith has a website L one training dot com that's got over 60 hours of training
videos on all those subjects and more.
When I first started out doing mobile, I utilized Keith's videos on module
programming and J 25 34 in order to get my head wrapped around what I would
need for the tooling, the computers, the software setups, you know, what kind
of obstacles I would be up against when I'm out there programming modules on
cars and it was a huge benefit to me.
And I continue to use the training videos that he has on his website.
So I strongly recommend checking out L one training dot com.
The link is in the show notes.
That's an important thing to know.
And then you need to be able to test to see how much ethanol is actually in the fuel.
That's 100 percent in this situation, something that could and has caused this
before both contaminated and the incorrect fuel.
But if you check the pressure and then you have like a, you know, a graduated cylinder
or even an empty Gatorade bottle, you can do a check of the fuel pretty easily at this point.
And now, if you know, you have quality fuel and the computer knows exactly
the ethanol content of that fuel that's going in there.
And you know that, hey, fuel is definitely getting into the cylinder
because it's full of it, right?
Now we can start looking at some other things here.
Now, are there possibilities where it could just be spraying too much fuel
based on a improper input, you know, coolant temperature sensor?
And there's other things that could cause this potentially.
But a lot of those can be eliminated just by looking at data
PIDs on like a key on engine off, right?
We can kind of do a rationality check of like, hey, do all my temperature sensors
make sense for where the vehicle sits right now?
And if it hasn't run in a while, they should all be pretty equal, right?
Are all the pressure data PIDs reading the way that I would expect them to?
Even a mass airflow sensor, sensor 100 percent
can cause a crank start stall.
You can look at, see what the data PID is there.
You can unplug the mass airflow in a lot of cases and see.
I will say when I've seen a mass airflow, I have that happen.
It usually doesn't flood out the engine, but I want to be careful there
because there's so many cars out there and it could definitely potentially happen.
But usually when I see the mass airflow cause that specific symptom,
it's not adding enough fuel.
And basically, you're not going to have a, you know, flooded engine
from a mass airflow most of the time.
Again, mass air flows are a dynamic sensor and they can fail in a lot of different ways.
I think I have done podcasts about that.
And I could do another one of mass air flows being probably the toughest
sensor on the car to really assess because it can fail at one point of its operation,
but not the other.
And we have no actual realistic way of measuring how much air is really going into the engine.
Like every other sensor on the car, we can make a measurement and see, like,
what is the actual fuel pressure?
What is the actual temperature?
But for the mass airflow, that's much more difficult.
Anyways, the whole different story.
So it is something to consider if you have these symptoms.
Now, the next thing and you will need the tooling for this is a big winner for me.
And it has been for a number of these vehicles, except for one of them this past week.
And I'll get to that.
But on the Honda, it was the winner is I went in cylinder at this point.
Now, because of the way the compression looked on this Honda, we were suspecting
that there could potentially be a timing issue.
And it just so happened on this O2 Honda Odyssey with a 3.5 liter that it was on the
back cylinder bank, which does not have a cam sensor, right?
That's the other thing is if you have a timing issue, you could definitely have some
of these symptoms as well.
I've had it where timing, mechanical timing being off in an engine causes it to flood
and create a no start at an ambient temperature where you shouldn't see an engine flooding.
And so that's something I want to look for.
But on this Honda, that back bank does not have a cam sensor, meaning we wouldn't
have a code for it.
Would it set a code cranking?
Anyways, I don't know.
I want to know to Honda, maybe not.
But it's not even monitored by the computer.
It just has a cam sensor on that front bank on these older three fives.
Oh, the compression is low back there.
We want to check it.
I went in with a WPS to see what does the what are the pressures actually look like?
And now through a relative compression, we saw they were a little bit low.
But I want to see, you know, can I compare maybe valve opening and see
is there something very obvious wrong with the cylinders going on back here?
And this is where I ended up finding that.
Oh, no, it's not that it's a valve timing issue.
It is the fact that we have almost five PSI of exhaust back pressure cranking.
OK, so we didn't even get the engine to start by the time I got to this point.
But I'm looking at that where zero is and where the exhaust plateau is.
And if you've never looked at a in cylinder compression waveform using the
Pico and a WPS, take a look and you can see the two peaks on either side.
And then the exhaust plateau will be in the middle.
And what that's representing is as the piston is traveling up in the cylinder
and the exhaust valve is open, you're going to see not only what the pressure
in the cylinder is, but what the pressure in the exhaust manifold is, right?
When the exhaust valves open, you're basically the what's happening
in the exhaust manifold and what's happening in the cylinder is the same place, essentially.
So if you have back pressure, you're going to see it there.
And it had five PSI of back pressure cranking.
OK, now it wasn't just on one side of the engine.
This was on both.
And it ended up on this Honda that it was a completely restricted exhaust.
Now, why did this happen on this Honda?
This was because it actually sat for a year and a rodent had gotten into the exhaust
and packed it full of it looked to be something like dog food.
And I've actually seen that happen a couple of times before had a forward focus
much earlier in my career as working at Firestone at the time.
And this one actually ran, but it was smoking like crazy.
And again, it's pretty early on in my career.
And I ended up saying, hey, there's something wrong, like,
internal the engine where it's burning a lot of oil.
Is it just it's billowing smoke out of this exhaust?
And I can't find, you know, whatever something obvious going into the cylinders.
And I kind of think it smells like oil, but it's got a weird smell to it.
I remember thinking that, well, it ended up, it was corn that had plugged up the exhaust.
Enough. So this one actually still ran, but it was causing the smoke to come
out of the exhaust as it was running.
And that one, I didn't do the final diagnostic on that.
It I think it ended up going back to the dealer and they found that.
But I never forgot that one because I was like, oh, that's smell.
Yeah, that could have been burning corn.
And when he was rodents get into the exhaust and they can plug it up.
And usually that's the vehicles got to sit for a long period of time,
like over a winter or that to happen.
But it can 100 percent happen if it's in place where rodent can
climb up into the tailpipe and make a stockpile of food.
And maybe you got a bag of corn or dog food in the garage.
It makes sense that it can happen.
OK, so that was that was the Honda.
And the WPS did it for me to see five PSI of back pressure while cranking.
Now, could you also potentially look at your manifold pressure at the same time
here and see that we're not going into any sort of a vacuum while cranking?
That's definitely a possibility, too, is to see that, hey, we're not pulling anything.
Now, we're not supposed to pull a real deep vacuum just while cranking,
but there should be something and you should be pulling something.
And if you can get it to start and watch your intake manifold pressure,
that's another thing.
And I actually was able to do this on a Ford.
I think it was a Mustang years ago that had this problem.
And I remember looking at the map sensor on this particular Ford,
and I could see that it was barely leaving atmospheric pressure.
And this thing would actually like it would like kind of start and run.
And it would briefly just chug a little bit and it would stall.
But it barely leaves atmospheric pressure in inside of the manifold.
And you could use a vacuum gauge.
You could look at the map sensor on it and see that.
And that's, you know, that's a sign pointing towards like, hey, you know,
we're not able to pull a vacuum on this engine.
Of course, there's other things that could cause that.
But one of them is we can't push any air out.
So we're not going to be able to draw any fresh air in.
So that's one, you know, reason that could happen.
Now, you have a vehicle like this to the oh seven Mustang with like a four oh,
you could disconnect the EGR to and that would allow it to start.
Now, a lot of vehicles, you don't have that option.
But if you do connecting the tube or whatever the connection is to an EGR,
that might be more realistic than pulling a no two sensor.
So keep that in mind.
You might have that on some vehicles and be able to do that.
So the other one that we did this week was a Chevy Silverado with a 53
And this, again, was also Frank Nostar cylinders.
The shop had been up and down on this one.
And they really weren't sure where they were going with it.
And on this one, again, this is the same week as the Honda.
And I was able to at least think about it as a possibility.
But I went for the WPS, this Chevy as well and 53 putting it in there.
And I did not have the what I would consider excessive back pressure
in the exhaust while cranking on this one.
Now, what I probably should have done is put it in right away before I did anything
because this engine, again, did start briefly and then it stalled out.
And then it was just really just a crank for me after that.
Maybe I would have seen some more back pressure when the engine actually started.
So it's kind of my tip here is like it's a hard one to really push.
Like, is that the first thing you're going to do on?
No, start is throw the WPS in maybe.
But I could see a whole lot of arguments
while I like that's not that should not be your first test.
So I don't know that I can really make that argument,
but it would have shown it to me in this case.
So hindsight says that's what you should have done
and probably would have caught it a little bit quicker.
Again, looking at manifold pressure,
I wasn't looking at it close enough on this one to really use that as my direction.
But I did go through just about everything else on this truck and say,
hey, I really do feel like we got to pull this O2 out of here and see
because I've done everything else and it's a 53
And I work on these things all the time.
And I'm like, these are not that complicated.
You know, it's air fuel spark and I've been through everything, right?
Checking the fuel, looking at the fuel quality,
making sure I have injector pulse.
I've got spark.
Did the relative compression and this did have a couple of low cylinders.
They were wet with fuel.
But again, getting good spark there.
And so I told the guy, I was like, hey, can we just yank one of these O2s?
I was like, pick either side.
It doesn't matter because it's a Y pipe on this one.
So you have two upstream converters that go back into a single one.
And so, like, really, you could pull any of these O2 sensors.
I'd prefer it's an upstream, but just pull any of them and let's see
if it changes our situation because it's not even trying to start
after that initial one.
So my guess is it has to be the most downstream converter
that's plugged up would be my guess.
And so you ended up pulling the O2 sensor out and it fired right up
almost immediately at this point.
And so, you know, OK, that's what we've got going on.
Now, to be totally honest, I don't know that I really would have pushed for that.
Had I not just had the Honda earlier in the week,
I might have gone through with some other tests.
And because that back pressure one, it wasn't conclusive for me.
And I was looking at the WPS with it cranking.
And I guess that's what I'm talking about on the show here, too,
is like you can't always rely on the same test method to give you the answer
on every single car.
That was the case in this one.
I don't know if it's because it's a V8 because it's got that big Y pipe.
Maybe I should have let it crank longer.
And maybe I would have seen the back pressure on that exhaust plateau.
But just cranking it, I didn't see anything that really stood out as a problem.
But the WPS does give you a lot of other good information like, hey, all my,
you know, my valves are moving in the correct way that I expect them to.
I have good compression on this cylinder.
You can use it to compare like where the spark timing is happening with the
rotation and, you know, the four stroke cycle.
That's useful information for something like this.
There is on those Silverados, there is something where the phaser pin can
stick and it'll cause it to kind of be out of time.
And that can cause a no start.
But usually you have a compression issue or you have some valve, you know,
the valve timing is going to be off because the phaser is stuck in a wrong
position and I didn't have that.
Everything looked like it was supposed to.
So I want to move me along to, hey, let's pull this O2 out and see what happens.
And that ended up being the case on this vehicle as well.
So anyways, that's why I'm going to wrap this one up.
I thought it was an interesting thing to talk about.
And I don't know, maybe you guys run into this out there more often than I do,
but I don't see it that often.
And I thought it was worth talking about on the show.
So thank you to everybody out there for listening.
I always appreciate it and I'll appreciate chatting with people.
If you shoot me a message on Facebook or an email, I'll try to get back to you
as soon as I can. Other than that, let's get out there.
Start fixing the world one car at a time.
About this episode
Diagnosing a no-start gets weird when the root cause isn’t fuel, spark, or immobilizer logic. The hosts repeatedly come back to restricted exhaust—often from a clogged catalytic converter—where the engine may start briefly then stall, or even progress to crank no-start. They connect symptoms to tests like combining multiple clues, checking injector pulse and spark, and confirming exhaust restriction by removing an O2 sensor (sometimes requiring an oxy-acetylene torch). Real cases include a 2002 Honda Odyssey with rodent-packed exhaust debris.
Last week we ran into a no-start condition that you don't see every day... but twice in the same week. Listen to find out the cause and diagnostics you can perform to pinpoint this issue. Vehicles mentioned, 2015 Chevrolet Silverado, 2002 Honda Odyssey, & 2007 Ford Mustang.
