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Backfire and stalling at idle when hot, followed by no start conditions *video included*


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Making a thread to stay out of my build thread for this issue

 

Started testing the car out this season. Trying to still narrow down the running/hot overheating issue and all the things related to it.

 

I'm still pending dyno time to get maps all sorted out and timing set straight.

 

In the meantime while driving I do hear a bunch of backfires and while driving around today in 5 o'clock traffic car started to get hot again, which seems to make the backfires worse. When I pulled into the driveway I let it idle to see whether it's just running hot or it's actually going to go into overheating. At some point in time it couldn't maintain idle, backfired a few times and stalled itself out. This follows by no start condition until it sits for a few minutes and cools down. 

 

This puzzled me as I'm not quite certain what could be causing all these backfires, is it my timing? Could there be something else?

 

It has never quit on me while driving and I can force it to stay running through the backfires. If I leave it running long enough it will get hot, then backfire more often and then lose idle which is followed by no start. 

 

At the end of day I started to try to balance the throttle bodies and got the video of it happening


As of right now I'm not running active IAC but rather just holding the butterflies open with an idle screw to maintain (somewhat high) idle. 

 

 

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I don't know where your coolant temp sensor is located but the expansion tank looks empty. The system could be empty above the sensor.

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It could be a lot of things, you need an AF sensor, you will learn more in 5 minutes that you will after hours of faffing around. Using a vacuum guage, go old school, try a piece of hose, stuff one end in your ear, he other and in the throttle body, with a little practice it amazing how good you will get. That assumes you have something like regular hearing. 

 

Graham 

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Looking at all your videos, I see you've had a few problems. Looks like you had a blow head gasket last year, were running without any antifreeze for a while (muddy water) which cal also clog the tiny holes in the head gasket, and a loose fuel pressure regulator on the rail. Is all that fixed?

 

Do you have an overflow for the expansion tank or do you fill it halfway?

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16 hours ago, MV8 said:

I don't know where your coolant temp sensor is located but the expansion tank looks empty. The system could be empty above the sensor.

 

 

Coolant temp is in the thermostat housing as I recall. Expansion tank is pretty low as I just checked but not empty. 

 

15 hours ago, Dave W said:

The engine is running lean at idle. I would clean the injectors. 

 

I'm at about 13.5 on the wideband at idle (bung is located after the cat converter so there is a delta of .5 to 1.0 at a guesstimate. Not sure in which direction)

 

12 hours ago, ashyers said:

Check your fuel pressure.

 

I'll double check but typically I'm at steady 40.

 

11 hours ago, fastg said:

It could be a lot of things, you need an AF sensor, you will learn more in 5 minutes that you will after hours of faffing around. Using a vacuum guage, go old school, try a piece of hose, stuff one end in your ear, he other and in the throttle body, with a little practice it amazing how good you will get. That assumes you have something like regular hearing. 

 

Graham 

 

AF wideband is mounted and I always keep an eye on it. I'll look into the hose option. I do have an auto stethoscope.

 

10 hours ago, IamScotticus said:

do compression checks. 

#3 might show something. 

 

Done compressions and leak downs last year but not going to hurt to do it again.

 

9 hours ago, coffee break said:

Burnt valve?

 

Maybe?

 

7 hours ago, MV8 said:

Looking at all your videos, I see you've had a few problems. Looks like you had a blow head gasket last year, were running without any antifreeze for a while (muddy water) which cal also clog the tiny holes in the head gasket, and a loose fuel pressure regulator on the rail. Is all that fixed?

 

Do you have an overflow for the expansion tank or do you fill it halfway?

 

You're not kidding with a few problems!  :classic_laugh: I don't believe head gasket was blown last year, I just ran out of things to replace so I replaced that too. I don't think I fixed any problems. Yes I was running water for a considerable amount of time as it got very expensive dumping coolant while troubleshooting. Water/coolant has been muddy since I bought the car about 5 years ago now. After replacing everything and flushing the block it's still starting to get muddy again. I have little junk floating around in the coolant system too. My see through coolant filter is catching the debris. 

 

Lose fuel pressure regular is resolved. I send the entire throttle body to get rebuild last year to the parent company. They told me old unit was "rough" and replaced almost everything on it. 

 

I have a lightly filled overflow for expansion yes. 

 

Pending getting a fuel rail from Redline but they are being a little difficult to work with. 

 

One big hint I should mention is that I've never had a tuner dial in the timing after changing the head gasket, so there is a good chance it can be off causing backfire. I'm still looking for somebody in the area to take the car to. In the meantime maybe I'll play with the cam gears (adjustable) myself and see if I can dial it to be smoother? Fairly certain Non SVT Zetec is non interference.

 

Thank you all for the advice so far!

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It has to be an A/F at idle or you would have noticed a drop in power thru out the whole power band Vs just the temp. If there is a power drop, then a cylinder leak down or compression check is needed. A very lean mixture condition at idle will have NO carbon band at the very end of the tip of the center spark plug electrode.

Could be a bad valve, but again you would have a noticeable power drop.

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There is a coolant temp sensor for the gauge and usually a separate sensor for the efi temp input. The efi temp sensor has a large impact on the mixture and the engine is most sensitive to mixture at idle.

FWIW, the bubbling coolant is typical of a failed head gasket or cracked head. A cold engine may not show a failed gasket with a compression test.

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There is a difference between misfire and backfire.  A misfire will sound like an missing cylinder, and will be visible in the data as a temporary lean condition.  Typical cause is injector fails to open, or ignition just doesn't take place.  If you've got a lot of spark retard it could be at the burn limit.

 

Typical backfire causes are incorrect ignition timing, incorrect injection timing, or too rich (unburnt fuel going into hot exhaust and self-igniting).

 

Without knowing anything about your engine controls it's tough to diagnose.  So ask yourself, if this only happens when hot, what changes?  Is the injection timing wrong when engine is hot?  If it was due to a burnt valve, why would you only get backfire when engine is hot and not all the time?  Fuel pressure typically has no engine temperature dependency.

 

Start eliminating potential problems and narrow down potential root cause.

  • Confirm ignition timing with a timing light.
  • Confirm air fuel ratio with a known good wideband lambda sensor.
  • Confirm all your engine control inputs, all temps and pressures at ambient before start after engine has sat a lot time?  All values plausible after engine has warmed up?  (Engine temp equals thermostat value, intake pressure below ambient at idle, etc.)

 

BTW, old VW diesels were famous for head gasket failure.  The symptom was bubbling coolant, but somehow it was still always clear.  I'd be pretty concerned about "muddy" coolant after several system flushes....  But this is probably a separate issue.

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On 5/6/2022 at 12:10 AM, Vovchandr said:

In the meantime while driving I do hear a bunch of backfires and while driving around today in 5 o'clock traffic car started to get hot again, which seems to make the backfires worse. When I pulled into the driveway I let it idle to see whether it's just running hot or it's actually going to go into overheating. At some point in time it couldn't maintain idle, backfired a few times and stalled itself out. This follows by no start condition until it sits for a few minutes and cools down. 

 

 

 

 

 

yes, this seems more like a backfire than a misfire.  Is that flame behind the throttle valve?  It almost looks like combustion happening.  The only way that should be possible is if spark happens when the intake valve is open.

 

Double check the injector and ignition wiring, and cylinder assignment.  This is the number one mistake on new engine controls setups.  Then, double check the ignition timing without fuel, with the starter cranking the engine.    Though, if the wiring was wrong, it shouldn't just happen when the engine is hot.  So you may have a few things going on, like too much fuel along with incorrect cylinder wiring.

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Posted (edited)
6 hours ago, GTIspirit said:

 

yes, this seems more like a backfire than a misfire.  Is that flame behind the throttle valve?  It almost looks like combustion happening.  The only way that should be possible is if spark happens when the intake valve is open.

 

Double check the injector and ignition wiring, and cylinder assignment.  This is the number one mistake on new engine controls setups.  Then, double check the ignition timing without fuel, with the starter cranking the engine.    Though, if the wiring was wrong, it shouldn't just happen when the engine is hot.  So you may have a few things going on, like too much fuel along with incorrect cylinder wiring.

 

Yes that is fire behind cylinder #3 and #4 on occasion. It seems to get worse when it runs hot, but I can hear it happening occasionally while driving and on decel. 

 

I DEFINITELY have a few things going on compounding on each other. Some are simply symptoms rather than the source. I'd hate to waste time chasing symptoms.

 

*Running hot/dirty coolant are definitely some of the primary core issues. However I don't think they are directly related to the backfire as it does happen during regular operation too. 

*Tuning in the timing after doing the headgasket change is also a crucial core issue I'll be addressing. 

*The mechanic (me) running out of skill is definitely a core issue in this puzzle :classic_unsure:

 

I've never done a timing check so I'll look into that. I'll also escalate getting to a tuner.  

Edited by Vovchandr
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6 hours ago, Vovchandr said:

 

Yes that is fire behind cylinder #3 and #4 on occasion. It seems to get worse when it runs hot, but I can hear it happening occasionally while driving and on decel. 

 

I DEFINITELY have a few things going on compounding on each other. Some are simply symptoms rather than the source. I'd hate to waste time chasing symptoms.

 

*Running hot/dirty coolant are definitely some of the primary core issues. However I don't think they are directly related to the backfire as it does happen during regular operation too. 

*Tuning in the timing after doing the headgasket change is also a crucial core issue I'll be addressing. 

*The mechanic (me) running out of skill is definitely a core issue in this puzzle :classic_unsure:

 

I've never done a timing check so I'll look into that. I'll also escalate getting to a tuner.  

@Vovchandr does the combustion event behind the throttle blade only occur on cylinders #3 and #4?  Never on cylinders 1 and 2?

Does it only occur at idle, never when the throttle blades are open?

I couldn't tell from the video, does it occur when revving up the engine and then releasing the throttle so the blades are closed?  (Does this only occur when ECU thinks it's in "idle" state?)

 

How does the engine run when cold?  Does it actually run smoothly, or a bit rough?

 

You said the coolant was always muddy, which implies the engine fine some time in the past?  What was done since then?  New ECU?  Changed wiring?  Removed and re-installed engine after some mechanical work?

 

I'm still tending to think wiring.  Maybe cylinder 3 and 4 injectors or ignition got mixed up if the engine ran fine before?  Coil on plug, distributor?  Make sure the wiring is absolutely correct before checking timing.  Even better, get a friend to watch you check the wiring.  By now you've been staring at this for a while, time to get a fresh perspective to double check things.

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I need to think about your backfire. I will recommend you flush the cooling system with baking soda. Put about 1/3 cup of baking soda in plane water and get the car up to temperature. Then flush it. Baking soda is a mild way to clean the system. 

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The Zetec ignition system uses a waisted spark coil. The coil fires cylinders 1 and 4 and 2 and 3 at the same time. When 1 is on the firing stroke 4 should be on the exhaust stroke. From looking at the video the backfire does not look very violent, and the engine ran reasonably smooth. I do not have any definitive answers, but I would look at cam and ignition timing. If I remember correctly, you could not find any cam specs for the cams in the engine. I would adjust the intake cam with a compression gauge. Adjust the cam to the highest compression reading.  This is out in left field, but do you know if your catalytic converter is plugged? Is it easy to pull off?   

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On 5/8/2022 at 8:03 PM, GTIspirit said:

@Vovchandr does the combustion event behind the throttle blade only occur on cylinders #3 and #4?  Never on cylinders 1 and 2?

Does it only occur at idle, never when the throttle blades are open?

I couldn't tell from the video, does it occur when revving up the engine and then releasing the throttle so the blades are closed?  (Does this only occur when ECU thinks it's in "idle" state?)

 

How does the engine run when cold?  Does it actually run smoothly, or a bit rough?

 

You said the coolant was always muddy, which implies the engine fine some time in the past?  What was done since then?  New ECU?  Changed wiring?  Removed and re-installed engine after some mechanical work?

 

I'm still tending to think wiring.  Maybe cylinder 3 and 4 injectors or ignition got mixed up if the engine ran fine before?  Coil on plug, distributor?  Make sure the wiring is absolutely correct before checking timing.  Even better, get a friend to watch you check the wiring.  By now you've been staring at this for a while, time to get a fresh perspective to double check things.

 

I have very brief data log of the backfire. It literally happened, I recorded it and made a post. I'll investigate into other cylinders next. In the video everything occurred at idle, but I can hear it while driving. I'll make better note of whether under load or not. 

 

I'm currently reluctant to keep driving it to avoid further damage until things get sorted out. 

 

I'd say the engine when cold is pretty smooth. 

 

Coolant has been muddy since I bought it and it sat for a long time prior. Only major change during my ownership is the headgasket fix, rebuilding of ITB's, fixing a misfire by swapping coil pack and reinstall of the engine after a clutch failure. 

 

Cylinder #3 used to have a bad misfire that's been fixed. 

 

15 hours ago, CarlB said:

I need to think about your backfire. I will recommend you flush the cooling system with baking soda. Put about 1/3 cup of baking soda in plane water and get the car up to temperature. Then flush it. Baking soda is a mild way to clean the system. 

 

I'll do that! I think I used a coolant flush kit last year, likely similar technique.

 

12 hours ago, CarlB said:

The Zetec ignition system uses a waisted spark coil. The coil fires cylinders 1 and 4 and 2 and 3 at the same time. When 1 is on the firing stroke 4 should be on the exhaust stroke. From looking at the video the backfire does not look very violent, and the engine ran reasonably smooth. I do not have any definitive answers, but I would look at cam and ignition timing. If I remember correctly, you could not find any cam specs for the cams in the engine. I would adjust the intake cam with a compression gauge. Adjust the cam to the highest compression reading.  This is out in left field, but do you know if your catalytic converter is plugged? Is it easy to pull off?   

 

Cat might be shot. When I did have a misfire issue it definitely got hot..

 

image.png.e7d0e6156379021c97e347a8c2e459ce.png

 

IMG_20210914_192955529.jpg

 

 

Luckily I have a secondary exhaust that I plan to de-cat. Or maybe I'll de-cat this one if its shot and leave the other one alone. 

 

 

 

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8 hours ago, Vovchandr said:

 

...fixing a misfire by swapping coil pack.... 

 

Cylinder #3 used to have a bad misfire that's been fixed. 

 

 

 

 

 

That's what I was looking for, something ignition, injection, or wiring related.

 

What caused you to think the coil pack was bad, causing misfire?  How was it before?  If engine is still misfiring, and catalyst getting hot (or was that before you replaced the coil pack) what makes you think the coil pack fixed it? 

 

Double check the wiring, paying particular attention to the afflicted cylinders.  Inspect the terminal seating.  I've seen terminals not fully seated which can cause intermittent contact.  I've also seen bad crimping cause short circuits between terminals.  Beep it out from end to end just to be sure (continuity is likely ok).  Then start wiggling wires.  My guess is it also happens when cold, you just don't notice it because engine isn't hot enough to cause backfire.  Look for lean glitches in the data recording, as that's symptomatic of fuel not combusting, i.e. missing spark.

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Posted (edited)
7 minutes ago, GTIspirit said:

That's what I was looking for, something ignition, injection, or wiring related.

 

What caused you to think the coil pack was bad, causing misfire?  How was it before?  If engine is still misfiring, and catalyst getting hot (or was that before you replaced the coil pack) what makes you think the coil pack fixed it? 

 

Double check the wiring, paying particular attention to the afflicted cylinders.  Inspect the terminal seating.  I've seen terminals not fully seated which can cause intermittent contact.  I've also seen bad crimping cause short circuits between terminals.  Beep it out from end to end just to be sure (continuity is likely ok).  Then start wiggling wires.  My guess is it also happens when cold, you just don't notice it because engine isn't hot enough to cause backfire.  Look for lean glitches in the data recording, as that's symptomatic of fuel not combusting, i.e. missing spark.

 

Infrared gun was my only real clue to any misfiring. I saw that the cylinder was drastically colder than others and that my cat converter was glowing/smelling as well it sounding odd/like a missing cylinder. 

 

I replaced both wires and the pack. 

 

Over the last 12 months I probably put about 500 miles on the car. Mid summer last year I was having the over heating issues etc, that caused me to tear it down for head gasket. Then finally put it all back together for the track day and then maybe drove it once before winter. Since winter I only took it out once and posted the results seen in the beginning of the thread. I knew I still had an issue as it did the 2 NJMP track days fine except it would start to run hot again at idle while waiting to go out on the track and then run fine while moving. 

 

I'll look into the wiring this up coming weekend when I continue to troubleshoot. I'll also potentially disconnect the muffler to see if a backpressure/clogged cat could be a concern. 

Edited by Vovchandr
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