Spark plug gaps closing causing bad misfire

[DriftCrazy]

Hey guys, I tried finding a thread related to my issue but I couldn’t seem to find anything so any help would be greatly appreciated.

I had upgraded my ignition system to the kit with individual red top coils and new wiring harness sold by ECS tuning a few months ago. Since the install the car makes a weird chattering noise from the coils 80% of the time on start up and every once in a blue moon while driving but only while idled at a light to which it slowly disappears after about 30sec-1min. I’m not sure if this affects my issue but thought I’d add it.

During these past few months I’ve been changing my spark plugs all with the (NGK bkr7e) and brand new ones every time to try and find the right gap to suite my stage 3 tune.
First gapped them to .24 (ran great on WOT but built up too much carbon for city driving), then new ones at .27, and then tried again with new ones gapped to .30 just over a week ago.
The car had been running great and not to rich since I’ve installed the latest plugs 15.5-16.5 AFR on idle until yesterday morning with temp of -15C (after it driving fine the night before) the car had a misfire soon after leaving my house. Sounded like just one cylinder until It then soon after felt like multiple and started running real ruff and almost stalling so I pulled over.

The only code I had was misfire on cylinder 4 but after pulling all my spark plugs out I found that both spark plugs in the cylinders closest to the firewall 3 and 4 I believe on either side of the motor had had there gap closed completely shut looking carboned up and smell of gas.
I then changed both spark plugs with spares I had gapped back to .30 and started the car...car ran great for 30seconds until I was pulling out to the main road and misfire return cause the car to completely stall and shut off on me. The car then wouldn’t restart until I held the pedal WOT and it started back up with the misfire present but with white smoke out the exhaust only when reved.

What could cause this? I was just under a quarter tank so wonder if bad/low fuel causing detonation, I didn’t hear any noise in the motor so don’t think anything is loose on top of the piston cause it to hit and close the gap, also was thinking maybe the crankshaft position sensor?
Also should I be running bigger gap with this ignition upgrade?

Thanks guys any help would be greatly appreciated 🙏🏽

[ReggieNoble]

Only thing you can do really without tearing it down is to use an inspection camera and see what is bouncing around in there. Doesn't sound like a simple fix sorry to say.

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[JustManson]

Talk to your tuner.

They should be looking at logs and inspecting the fuel trims from idle to WOT to see if your actually running within spec for AFR on a stage 3.

I don’t have red top coils I’m running stock coils, same plugs at .024 on a stage 3 tune. I see 11 WOT and 14-15 at idle and city cruising.

I did have a fuel issue on my latest build which was running extremely rich at idle... actually wouldn’t let the car start and fuel was draining out of the exhaust. Killed the fuel pump by pulling the fuse and the car started.... lots of White smoke... sound familiar?

Maybe your tune just needs a tweak.


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[mikeb17]

I had the same thing happen and unfortunately something made it’s way into the cylinder. Crappy part was that the engine was a swap in I never tore into it so it was someone else’s doing. I’ll dig up some pics.

[Mille Bornes]

There are borescopes/inspection cameras on Amazon for fairly cheap. Stick one of those down the spark plug holes.

Also, AFR should be 14.7 at idle so you got something going on there

[mikeb17]

All I could find. Hopefully your plugs aren’t looking like this. If so then I fear for the worst.


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[CELison]

Spark plug gap coming completely shut points to a mechanical issue. Same thing with the smoke. Bad gas, or CPS will not cause those problems. I wouldn't drive the car at all, and borescope your holes as said above. Your afr is also off pretty far. Sounds like you need to talk to your tuner as well if it's not a hardware issue causing your afr to be lean. I would think you have some pretty major issues going on here.

[wbrunner23]

Something is physically making contact with your spark plug to cause it to completely close. Try to figure out what that is

[Zba]

A broken valve will do this. Good luck.

[DieselElectric]

Does your car burn any oil?

One of my old e30s would do what you are describing, it would build up so much carbon on one of the cylinders that it would bridge the gap a misfire.

But, that was on a 300k m20.

If the electrode is actually getting pressed in and closing the gap, you have an issue.

If carbon is bridging the gap, you still have an issue.

Compression test, leak down test, report back.

[DieselElectric]

Forget what I said about carbon. Too quick to respond. You need a bore scope. Probably will need to pull the engine from the sounds of it.

Last time I had a spark plug suddenly get the gap closed up, a piece of piston ringland had broken off and smacked it before exiting out the exhaust valve (got lucky there.) That was on a supercharged 2.2 Ecotec.

Before that, I had it happen on a 3.1 60* GM after a 125hp wet shot didn't go well. That engine wasn't running after that though lol.

So yes, carbon build up closing the gap isn't the end of the world, and it should take a while.

Gap closing up in a few minutes means mechanical interference, something broke.

[DriftCrazy]

Thanks for the replies guys!

Unfortunately I’m out of town for the week for work so won’t be able to troubleshoot till this weekend.
I’m definitely going to get a borescope and check inside the cylinders to see if I can see anything, but would this only cause on side and not both spark plugs on either side of motor to close shut?

I’ll do a pressure test aswell on all cylinders just Incase the piston is the issue

Also I’ll take a look into the tune because I agree the AFR does seem off
I’d post a pic of the plugs but I’m not sure how to do that on this thread

[ReggieNoble]

Thanks for the replies guys!

Unfortunately I’m out of town for the week for work so won’t be able to troubleshoot till this weekend.
I’m definitely going to get a borescope and check inside the cylinders to see if I can see anything, but would this only cause on side and not both spark plugs on either side of motor to close shut?

I’ll do a pressure test aswell on all cylinders just Incase the piston is the issue

Also I’ll take a look into the tune because I agree the AFR does seem off
I’d post a pic of the plugs but I’m not sure how to do that on this thread

Did you last plugs have screw on tips? I've seen the tips unscrew themselves before, but to have two at the same time would be miraculous but possible I guess. So if you have all the olds plugs you may want to check them.

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[neilthewheel]

Hopefully that is the result of somebody just dropping the plug in the hole and coming back for it with the socket, instead of putting it in a socket that holds it properly, and gently guiding it into the right position.

Pretty much all of the other potential causes are in "just get a new motor" territory.

[vavJETTAw36]

Sounds to me like your startup open loop fueling values need to be adjusted. turn the ignition on and wait 5-10 for your wideband sensor to warm up. Then start logging it. Turn the key and record.

[DriftCrazy]

I do all the work on my car myself so believe me I did not drop anything into the cylinder and I’m always very careful with gapping and installing my plugs so I know that shouldn’t be the issue.

vavJETTAw36: that’s not a bad idea I’ll have to check that aswell because now with the new ignition setup it might require an adjustment in values....I’ll test this weekend and report back!

[m_haiser]

afaik your fuel trims are a FAR secondary problem to gap closing on the plugs and probably totally unrelated.
rent/borrow/buy a borescope and look for contact between plugs/valves/pistons

[DriftCrazy]

Hey guys!
So I will be checking the car tomorrow hoping it’ll be a little warmer than tonight because it’s -25C right now.
I just had a quick thought...could my issue possible be due to carbon build up on top of the pistons from running too rich from the previous gap settings on my plugs and maybe with my current setup it’s all breaking off and possibly cause the plugs to close from build up contacting between piston and plug??

Just trying to be a little optimistic and not rule anything out because after I just blew my RB25 in my 240 last year and then had to scrap my other Audi 2019 really isn’t off to a good start with my S4 😞

[DriftCrazy]

Hey guys ******update *****

So I checked out the car today and hereÂ’s what I found out
- after looking with borescope in all cylinders I do not see any debris or damage to the pistons or sidewalls at all
-all spark plugs are still ok including both I had replaced when I was on the side of the street even after the second misfire occured (I thought the gaps would had closed immidately like the ones I just removed)
-tested all coil packs and no issues
-tested all wiring harnessÂ’ and no issues (didnÂ’t assume there would be as all brand new but you never know) (grounds good aswell)
- checked my fuel pressure regulator and all seemed good (rated for 4bar as I have stage 3) was thinking it could be cause to detonation somehow
-car doesnÂ’t burn any oil and the coolent is still full

Right now IÂ’m more confused than ever as to what could have caused this issue, but if all my electrical components (plugs/coils..) all test out fine than the issue might be fuel related or possibly timing? Camshaft sensor maybe?

Also one thing I found odd was that all my pistons looked dirty except cylinder 6 (first cyl on front driver side) look cleaned.. this spark plug was fine and was not one of the ones that had closed, but could this mean maybe clogged injectors?

[DieselElectric]

Compression and leak down tests.

[neilthewheel]

Did you drop the plugs in the hole and close the gaps when they hit the bottom?

[01yellercobra]

I had an issue with plugs randomly closing on a previous build. Turned out I was getting detonation in that cylinder. Everything got so hot it causes the plug to close up. And the pock marks on the piston showed I was getting a lot in that cylinder. But that would only happen after a hard WOT pull. If it's closing at part throttle I'd say something it hitting it like everyone else.

[DriftCrazy]

Hey guys, so I’m outta town this week again but I will do a compression test this weekend to see what I get on all 6 cylinders so I can compare the two that had the plugs close on them.

Also the plugs did not drop in the hole causing the gap to close as I had been driving with these plugs in for about a week before the misfire, I’m also very careful when working on my car

And oh ya? What was the solution to your issue of the heat on the cylinder?
Because the night before I did do a couple of WOT pulls so maybe the issue happened before the morning of the misfire? It also was a very cold morning so I’m assuming the hot/cold didn’t help my issue

[DriftCrazy]

And oh ya? What was the solution to your issue of the heat on the cylinder?
Because the night before I did do a couple of WOT pulls so maybe the issue happened before the morning of the misfire? It also was a very cold morning so I’m assuming the hot/cold didn’t help my issue

[DriftCrazy]

Hey guys back with more info!
So I did a compression test on all 6 cylinders and all came back between the 150-160psi..so all perfect!

I decided to clean all electrical components (harness/plugs/coils) and put car back together to start up and see what happened.
After start up the car idled great and nomisfire present till about 5 minutes in small misfire (stuttering occured), I then checked each injector (the old trick of putting a flat head to the top an listen for the ticking to ensure there firing properly) and all sounded good.
The misfire soon disappeared once the car began to heat up. After about 15 minutes of idling I then took the car for small tour around the parking lot to which the misfire became intermittent. Like it was there misfiring and then all of a sudden it was fine and running and sounding great with even AFRs sitting at around 15.3 at idle. Even during the misfire the AFRs seemed to be reading fine. The misfire doesn’t occur right under throttle, it’ll run good for a bit then randomly not good during driving and sometimes at idle

Any ideas???

[Timtheguru]

Need to check timing, the piston could be hitting the plug. Will need to pull the valve covers to check that the cams are also properly timed.

[Mille Bornes]

Need to check timing, the piston could be hitting the plug. Will need to pull the valve covers to check that the cams are also properly timed.

How could timing make a piston hit a plug?

[mikeb17]

How could timing make a piston hit a plug?

It can’t


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[DriftCrazy]

I don’t think timming is the issue because the misfire comes and goes and if it were to be timming the misfire would be continuous would it not?

Any other ideas?
I’m starting to think it’s a fuel issue and that maybe my injectors or fuel filter are little clogged.
So I bought some fuel cleaner (Gumout High Mileage Fuel System Cleaner) and I’m going to add that to the car later tonight along with a full tank of shell 91 and see what happens 🤞🏼

[DriftCrazy]

Compression and leak down tests.

All Cylinders between 150-160psi

[julex]

"The car had been running great and not to rich since I’ve installed the latest plugs 15.5-16.5 AFR on idle" - that's not normal. Normal ratio is 14.7:1. Running this ration on a bank will result in some cylinders actually being much leaner too as the ECU is trying to get to 14.7:1. It seems to me like you might be overheating the plugs and that is what might be causing the gap to close.

[DriftCrazy]

"The car had been running great and not to rich since I’ve installed the latest plugs 15.5-16.5 AFR on idle" - that's not normal. Normal ratio is 14.7:1. Running this ration on a bank will result in some cylinders actually being much leaner too as the ECU is trying to get to 14.7:1. It seems to me like you might be overheating the plugs and that is what might be causing the gap to close.

Yes so since I was in the motor I took a look and found a vacuum hose a little lose heading from my FPR towards my AFR gauge so after tightening it up on idle I run “as of right now”
Idle: 14.2-15.5
City: 13.5-14.5
Haven’t done a WOT test yet (highest boost I’ve gone is 15psi) as I’m afraid it may cause misfire again and me stuck on the side of road in -30 Celsius

Are these readings proper?

Car misfires rarely now so still unsure where my problem was or may still be

[slowSfaux]

This car has all kinds of problems. Do yourself a favor, pressure test it. There's a couple of guides on how to make your own for like $20 at a hardware store, or buy one online. That's step 1 in troubleshooting just about any B5 s4 problem.

[Mille Bornes]

Definitely pressure test. Smoke test if possible. I've found, when smoke testing, that large leaks can hide at little hoses. Where if you smoke the entire intake it might not show. So I'd check some of the smaller hoses individually.

Once your car is warm, your afr at idle and cruise should be 14.7. I wouldn't worry about fluctuating up and down a tenth here and there but the range you listed is much too broad.

[Mille Bornes]

What are your fuel trims?

[Pete6641]

Did we ever figure this out? its just happened to one of my friends S4 and closed cyl4 gap to almost nothing he's putting in a fresh one now to see if it happens again5900989761.jpeg

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[1thenaton1]

in another related but different issue, my cylinder 4 plug blew way out, and also seemed to cause cyinder specific misfires, occaisionally

[Bordom]

These all point to fueling issues

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[CELison]

^ yup. Cylinder temps way too high. I would look at the injector as the culprit first.

[cjt671]

Any of you with magic closing spark plugs running water injection?


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