Thread: EGR codes, Misfire #3, new EGR, now random misfire under boost

2004 GTP purchased a few months ago, ran pretty well.
I'm a mechanic, but this problem is kind of weird..
Initially i noticed an occasional stutter or hesitation / misfire on low speed, small throttle openings.. and the cranking times were getting long. It used to start with a quick tap of the start position but then required up to a full second cranking to get it to actually start instead of cough and immediately die.
I had pulled two EGR codes from the computer before, and obviously a sticky EGR could lead to the problems, so i was planning on changing it anyway.. then yesterday it got strange.

On the highway, almost at my destination, it dropped one cylinder (at least) and started flashing the check engine light constantly. The light stopped flashing after maybe 10 seconds so i went the last 2 minutes to my destination. Drove it home again afterward and while the CEL never came on it did misfire at higher throttle positions and RPMs so i babied it home. Pulled codes and found the EGR codes again and a misfire cyl #3. Since cyl#3 is right next to the EGR port i figured that might be related, so i bought a cheap EGR and installed it last night. When i installed it, I did clean the flange surface but the valve did not seem to sit well on the flange, as though either the flange or the valve was not flat and this was making the valve rock slightly. But i went ahead and installed it anyway.

First test drive, It starts like it used to (quickly) but i hear a hiss when on the throttle and can feel a stuttering misfire (especially at boost) making me think the egr is not sealing up well (or the coil is going bad).
I take the egr off (the hardware was not as tight as i expected) and inspect it and the flange, everything looks fine so i put it back on, a little tighter this time.
Slightly less hiss, but otherwise No change.

The gasket i used was a thick papery style with the screen on the exhaust side, but it is terribly conforming so maybe its not offering enough crush to seal.
I'm thinking about using a graphite style.
I'm also considering picking up a coil for 3/6 just in case that is the issue now.

Anyone have any input on this?

edit; the thick papery gasket is NOT terribly conforming..

and now i replaced the coils, with no change.

Originally Posted by Scottydoggs

so you know, #3 is the middle front.

back 2, 4, 6
front 1, 3, 5

flashing cel typically means you need a tune up super bad, or the cats clogged up. but this is at wot for the most part.

3 is also the piston that likes to chip, its a heat sandwich. so if you have not pulled its plug, pull it, see if its smashed. if it is, the piston chipped.

Thanks for that. for some reason i thought #3 was driver's side front.
pulled the plug, tried to post a picture but i got an over quota message..
Anyway, there's no damage aside from obvious melting of the center electrode and a massive gap.. i'd guess well over .080"
Trying to decide on what plugs to go with. I'm hard on the pedal and a fan of iridium for anything like this, as well as likely to do some upgrades in the future..

i replaced the plugs since #3 looked so ****ty. The rest were no better. Used the same wires. for now although i did buy new. it started to rain and i didn't want to deal with it.
No change in running, still gets all stumbly and misfiring at higher RPM and throttle position, which makes me think i melted the cat the other day on the way to work.

evidence; occasional exhaust smell from AC, pressure hiss under boost (when it will get into boost) falls on its face above certain load levels with random misfires but no codes related to that yet oddly enough

heading out for a ride do so some data acquisition

Originally Posted by BillBoost37

The EGR codes could explain a bit here.

An EGR flow code can be the map sensor not reading properly or at all and that will never be fixed with an EGR valve swap.

I will be pulling data from that sensor specifically on my road test now

Soo.. it seems at least 95% better now for no apparent reason. I just put a fresh tank of fuel in it and it seems happy. Weird considering this is my daily driver.
No misfires, and maybe only a hint of hiss at full throttle full revs.
I know i should just be glad, but i like to understand why it was screwy in the first place.
I'll just monitor it for weird behavior/

Anyway, thanks for the help

Now it seems 100% when cold, but still messes up when hot.
And the hiss is definitely still there at WOT
I'm going to replace the EGR gasket and try to test for backpressure while its off

No codes present at this time.
Replaced EGR gasket last night, no more hiss, appears to have been a boost pressure leak.
Currently no misfire at upper RPMs but now its stuttery at low throttle openings.
O2 sensor was showing a shortened range of voltage swing. Considering doing that and snaking a camera in the port to check the catalyst matrix for melting

The codes that were present were 303 404 and 405