I have a persistent problem and it's cause is mystery.... can anyone provide some advice?

(2001 Audi B5 A4 1.8TQ stock)

Here are the symptoms:

1. Engine stutters between the 2k-3k RPM range.
2. When it does I get a blinking CEL, code reads P0304 - intermittent misfire on Cyl. 4

Things I've done so far with limited success:

1. Swapped coil packs (code doesn't follow).
2. Changed spark plugs
3. Removed injectors, had them cleaned and flow rated

I'm wondering if it's turbo/boost related. Maybe a line is collapsing somewhere under pressure or there is a boost leak? I dunno... thoughts?

Thanks!

 

If the code is always cylinder 4, it's hard to imagine it being something that isn't specific to cyl 4 alone. And you've isolated plug, coil, and injector. Did you actually swap injectors?

The only other thing specific to cyl 4 is the big one, compression. I wonder if you burnt a valve or something.

 

The injectors are actually from a donor car that I shipped off to get cleaned and matched.

If it is a burnt valve 1) how would that have happened? and 2) wouldn't the issue be consistent regardless of plugs or injectors (the engine stutter is of varying degrees, some days it's really bad, other days it's nonexistent, especially after the injector job)

 

I was just using burnt valve as a general guess for compression. Things like boost, MAF, etc. wouldn't be specific to one particular cylinder. So it's down to plug, injector, coil pack. Since you seem to have those isolated, you almost have to look at compression.

 

Good thinking! Looks like the next step is a compression test, then.

Could there be a possible explanation for the variance in the stutter? Sometimes it does it, sometimes it doesn't.

 

I don't know about the variation in the stutter. If someone has another idea what might stay at cyl 4 and not show up in other cylinders, speak up.

 

had this issue on my 97 , the answer was easy i had a worn out valve seal / guide and it kept on fouling my spark on that cylinder , the plug would come out dry because the oil would burn but once it got a little more bad and worn out i began to see the wet plug. The car would shake and jerk from 3k-4k at first it did it under full throttle only then it did it all the time even under normal acceleration.

so yea thats my untold tale.

 

Ok. Mine does it under accel as well, sometimes bad, sometimes not at all. I'd really hate to have to take the head off. It's worth noting I don't have any smoke coming from the back during acceleration.

 

Maybe the cam lobes that open and close Cyl 4's valves are a little worn down or have some type of deposit on them screwing up the timing?

Other than that i'd put my money on the Valve seals.

 

A little more details... while changing the thermostat housing I noticed oil below the throttle body where it connects to the hose and in the hose itself. I've ordered a compression test kit and will get the readings posted once I have the numbers.

Additional note: I have not once seen oil smoke coming from the tailpipe.