Misfires and hold cylinders

[Robdukes]

I have a few suspects on whats causing the issue. Wanted to tell it on here to see what you guys think.

Coasting down a long hill with a stop sign at the bottom. As soon as I pull off from the stop I get the EPC light and CEL. Car is sputtering/stuttering. Pull over and I have 2 cylinder misfires and hold cylinder codes on obdeleven. Along with intake air flow low, rpm request from transmission, and maf/map throttle position.

So decide im going to change the spark plugs (was overdue a bit), clean the throttle body and the MAP sensor in the throttle body. During this process I discovered the throttle body was so gunked up it wasn't closing all the way. The map sensor was just a glob of gunk as well. Also the snow screen was really clogged.

Cleaned up these things. Couldnt get NGK plugs within a decent time frame so I was forced to use the best ones I could get from advanced auto. But they were the correct gap etc. Noticed I needed a valve cover gasket while changing plugs as well. Finally its all back together, I clear all codes and run the throttle body adaptation through OBDeleven.

Take the car for a spin and all seems well. No codes.
Then 2 days later I go to hammer down for a pass and I get the EPC light, car stuttering. No CEL this time at least. One of the cylinders misfire and hold cylinder. Park, clear codes, wait 5 mins and car starts right up no problem.
Over the past week its been doing that more and more to the point now where if I give it enough throttle to downshift 2 gears its going to happen every time.

So the CEL codes haven't come back. I believe the combination of cleaning the snow screen, intake, and map sensor cleared those up fine. Its just the misfires and EPC light now.

I'm thinking it may be my cats. Ive been meaning to do them for quite some time. The car always puffed out huge clouds when I would pull away from that stop at the bottom of the long coasting hill and just so happens..thats exactly where this problem manifested the first time.

Anyone else experience a similar issue when cats were going/gone? I didnt do ignition coils, but since its not always the same cylinder I didnt think they were the issue.




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[Robdukes]

Some pics of the gunked up throttle body for your amusement. https://uploads.tapatalk-cdn.com/20210211/6520498c0b252f10e5dd5aac71a614e5.jpghttps://uploads.tapatalk-cdn.com/20210211/e24b671190ddce1bb9cf474c0fab8f86.jpg

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[djn876]

That's a lot of oil. Has the PCV been done? Otherwise that sounds like an intercooler leak more than cats.

Did you check the MAP sensors on each bank as well to see what they looked like.

You can check the cats pretty easily with a boroscope and pulling the o2 sensors.

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[Robdukes]

That's a lot of oil. Has the PCV been done? Otherwise that sounds like an intercooler leak more than cats.

Did you check the MAP sensors on each bank as well to see what they looked like.

You can check the cats pretty easily with a boroscope and pulling the o2 sensors.

Sent from my SM-G988U using Audizine Forum mobile app (http://r.tapatalk.com/byo?rid=87676)PCV hasn't been done. Im doing the other 2 MAPs my next day off here when I do the valve cover gaskets. Thanks for the advice about an intercooler leak. Didnt realize that could cause these symptoms.

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[djn876]

Yeah it is definitely one of the symptoms. What was the actual gap on the new plugs? I don't think that is your issue, but should be around .028 for stage 1. Coils are not likely an issue either.

With that amount of build-up, you could have a lot on the intake valves as well which could be causing you issues. You should probably pull the charger and look at the manifolds/intake valves for carbon or evidence of intercooler leakage. How many miles on the car?

[Robdukes]

Yeah it is definitely one of the symptoms. What was the actual gap on the new plugs? I don't think that is your issue, but should be around .028 for stage 1. Coils are not likely an issue either.

With that amount of build-up, you could have a lot on the intake valves as well which could be causing you issues. You should probably pull the charger and look at the manifolds/intake valves for carbon or evidence of intercooler leakage. How many miles on the car?I'm at 131k. I better double check the gaps. Positive its .028 for stage 1?
I haven't had much coolant loss. Over the almost 5 years I've had to add a very small amount twice.

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[djn876]

I would say based on the added boost it is definitely lower than the stock gap of .032, I thought .028 for stage 1 and .026 for everything else, but I just searched and EPL even just says stock plugs on .026 for everything except CA 91 DP tunes.

Honestly that's probably not a significant contributor for you though maybe not helping things. When my IC was leaking, the coolant loss was not significant at all and hard to tell because it occurred over such a long period of time. After seeing your miles and oil build-up, I am going to say you should do a carbon cleaning, and replace the PCV while you are in there. Consider t-stat and water pump if not done in a while since you are higher miles and you are in there already. I would think you will resolve most of your issues that way. Clean the SC as well while it is off, probably kind of gnarly inside.

[Robdukes]

I would say based on the added boost it is definitely lower than the stock gap of .032, I thought .028 for stage 1 and .026 for everything else, but I just searched and EPL even just says stock plugs on .026 for everything except CA 91 DP tunes.

Honestly that's probably not a significant contributor for you though maybe not helping things. When my IC was leaking, the coolant loss was not significant at all and hard to tell because it occurred over such a long period of time. After seeing your miles and oil build-up, I am going to say you should do a carbon cleaning, and replace the PCV while you are in there. Consider t-stat and water pump if not done in a while since you are higher miles and you are in there already. I would think you will resolve most of your issues that way. Clean the SC as well while it is off, probably kind of gnarly inside.Since I'm doing the valve cover gaskets anyways I'm going to put the NGKs in. Guess I'll gap to .026 since that's what the tuners are saying is best.
Youre right, its definitely time to do the PCV, thermo, and pump. Ive noticed the air will blow cold at idle sometimes lately.
The cats have been smelling for awhile now. I know I need to do them. Just such a pain of a job.

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[Robdukes]

So I pulled the plugs again and gapped them to .026
The autolite iridium xp's claim to be exact fit and say .032 gap from factory. They were actually at .045
It's my own fault. I thought I knew where my gap tool was and in the midst of doing the job I couldn't find it. So I trusted they would be OK since the NGKs and the Autolites both said .032 was exact fit on advanced autos website.
Never did find my tool but picked one up yesterday. I didnt think the gap would be the issue since .032 isn't that far off of .028 or .026.
But they were all at .045 and that was absolutely the issue.
Just went on a 45 min ride with no misfires at all. https://uploads.tapatalk-cdn.com/20210215/6ffe5e8845c11f1d3ace74d16513ad4b.jpghttps://uploads.tapatalk-cdn.com/20210215/895248be2cb9d471abc3a32c8b65516e.jpg

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[MSq5]

FYI, those coin type gap tools are not good for iridium plugs. The fine wire iridium tip is damaged easily if it is scraped. Best to use feeler gauges and gapping tools that avoid touching the tip when bending the ground strap.

https://c1552172.ssl.cf0.rackcdn.com/859684_x800.webp

[Chris@EPL]

And get rid of those AutoLites and get some NGKs.

[Robdukes]

And get rid of those AutoLites and get some NGKs.Hi Chris. Absolutely. They are on order. Was an emergency situation and none of the local places had NGK. Cant believe how far off the gaps were from what they claimed.

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