misfiring AEB engine - 98 A4 1.8tQ

[EOD-5]

hey guys, ive had this posted on Fourtitude and AudiForums but havent come up with a good solution yet...i know there are tons of misfire threads but i wwanted to get this one made and see if anyone can help

here is my situation. i bought the car with some of the mods below: Piper Cams, GIAC chip, Borla catback, FMIC, atmosphere vented BOV, and an adjustable FPR. It also came with a solid CEL

the car misfires bad at idle in all cyls, most dominantly in cyl 4, then 2, then 1, then 3, with VAG readouts i can watch them climb by the second...really fast

also, on a cold motor i will have hesitation / stutter from idle to ~2000 rpm, after that it will remember to drive and go well....this isnt there when its warm, but idle misfires are

my readouts usually look like this:

5 Faults Found:

16684 - Random/Multiple Cylinder Misfire Detected
P0300 - 35-00 - -
16688 - Cylinder 4 Misfire Detected
P0304 - 35-00 - -
16686 - Cylinder 2 Misfire Detected
P0302 - 35-00 - -
16687 - Cylinder 3 Misfire Detected
P0303 - 35-10 - - - Intermittent
16685 - Cylinder 1 Misfire Detected
P0301 - 35-10 - - - Intermittent

Things replaced so far:
- Spark plugs with NGK BRK7E 0.028 gap (did not help, now running Bosch F6DTC triple electrodes)
- ICM / power stage module
- all 4 coil packs
- engine coolant temp sensor
- cleaned MAF (with spray)
- checked and re-wrapped coil pack harness with silicone wrap
- intake manifold injector seats
- injector o-rings

i am waiting on the hose to reroute the DV back into the TIP, until then I am running the BOV still and will put the DV in soon

the car is on temp tags till the 17th, been playing with this issue since march 17th, so i would really like some help if anyone can....

thanks!

[EOD-5]

here is the most help i have had so far, but nothing worked

http://forums.fourtitude.com/zerothread?id=3784392

[JohnnyG]

"that is where im fuzzy..... no i dont know the reason or the breakdown ...bought it like that i believe when he put the Cams in he replaced valves and everything in the head area and then for some reason he needed to rebuild the bottom end, and then put it all back together not sure tho, would love details but unfortunately i dont have them"


after hearing that I would rule out mechanical causes first.
compression, leak down, check timing marks first crank and cam pulley then pull the valve cover and check the cam sprockets...should be able to align the notches w/ the arrows on the cam caps

[EOD-5]

"that is where im fuzzy..... no i dont know the reason or the breakdown ...bought it like that i believe when he put the Cams in he replaced valves and everything in the head area and then for some reason he needed to rebuild the bottom end, and then put it all back together not sure tho, would love details but unfortunately i dont have them"


after hearing that I would rule out mechanical causes first.
compression, leak down, check timing marks first crank and cam pulley then pull the valve cover and check the cam sprockets...should be able to align the notches w/ the arrows on the cam caps

i did a leak down test, thats where i got the leaks i found earlier and fixed...im going to do a compression test this week when i either find my tester or buy a new one....

can you explain a little more about the 2nd part of it though...

[EOD-5]

also have a question about MAF sensor.....what is unplugging it supposed to reveal....i did like someone suggested and it ran like crap, idled okay, and misfires went away...but really it looks like the misfire counter was just disabled

is that right? or ... i dont get it....how is that supposed to rule out or verify the operation of the MAF?

[ibew5audi]

I'm sure this isn't your problem but I recently did the icm/coil replacement for the same reason. One of my new coils was bad so maybe your new icm?? I had to use one of my old coils and 3 new ones. Any friends with aeb's? Do swaps with known working parts maybe with local ziner. Might be ecu.

[EOD-5]

unfortunately i dont have any around here, ill look around though haha

thanks :)

[creechsa4]

possible bent valves from valve float possibly. do you have upgraded valve springs for your cams? i've floated and bent some exhaust valves before & would misfire like a mofo. the valves would seal somewhat enough to run, but underway misfires golore.

or maybe you're fuel pressure too rich? just throwing stuff out there.

[creechsa4]

also how do your plugs look after a run? rich/lean?
what's your vac @ idle?

[pipe7284]

check your ICM, pull out the spark plugs and check if there is any oil on them. what had happened to my girls jetta was that it was throwing misfireing codes and replaced coils, sparkplugs, etc... and it ended being that the head gasket was blown and there was oil inside the cylinder causing it to misfire. check it out.

[EOD-5]

possible bent valves from valve float possibly. do you have upgraded valve springs for your cams? i've floated and bent some exhaust valves before & would misfire like a mofo. the valves would seal somewhat enough to run, but underway misfires golore.

or maybe you're fuel pressure too rich? just throwing stuff out there.

i dont know / think the valves were upgraded....the thing is the car runs AWESOME, very strong...just misfires at idle conditions

i really dont want to take the engine apart, im not too good with internals on combustion engines, i come from rotary where i can rebuild one in about 2 hours

also how do your plugs look after a run? rich/lean?
what's your vac @ idle?

plugs are clean, a little black but dont look terrible....vac at idle is around -10

check your ICM, pull out the spark plugs and check if there is any oil on them. what had happened to my girls jetta was that it was throwing misfireing codes and replaced coils, sparkplugs, etc... and it ended being that the head gasket was blown and there was oil inside the cylinder causing it to misfire. check it out.

ive replaced the ICM....spark plugs = no oil...

[EOD-5]

up

[bass_lover1]

plugs are clean, a little black but dont look terrible....vac at idle is around -10

Should be at 20-22 inHg, sounds like you have a vacuum leak somewhere.

I had something like this as well, wasn't nearly as bad. I had a vacuum leak only present at idle, and I'd get misfire only during idle.

Check all your lines and check valves.

[creechsa4]

i dont know / think the valves were upgraded....the thing is the car runs AWESOME, very strong...just misfires at idle conditions

i really dont want to take the engine apart, im not too good with internals on combustion engines, i come from rotary where i can rebuild one in about 2 hours



plugs are clean, a little black but dont look terrible....vac at idle is around -10



ive replaced the ICM....spark plugs = no oil...

cool, i agree with others on the vacuum leak via your boost tester... when i had bent exhaust valves, my idle was -7ish psi. hopefully it's just a vacuum line somewhere leakin somewhere. check your under-manifold lines as well.

[EOD-5]

guess ill do a boost tester again....when i idle i get -10....when i drive a bit and take my foot off the gas but stay in gear it drops to around -20

but as soon as i take my car out of gear and let it fall to idle rpms, it goes back to -10

so that is WRONG? ill check everything again....hope its not valves

what would be some bad signs when performing the test? i noticed that when the engine is off and i do a boost leak test that it pressurizes my oil cap a lot and if i take it out itll gush some air

although i never set my engine at TDC to do the test so cyls were still open, is that the problem?

[iin10ded]

the 2 things that glare out to me are [1] your atmosphere vented BOV, it's well documented that our ecu's prefer a recirculation valve as they need to account for the blown-off air. and [2] the cams - i'm not sure if the different cam will change the expected vacc at idle? but it seems likely that a cam install issue would lead to a misfire reading by the ecu. a vacc leak would not cause a misfire.

[EOD-5]

the 2 things that glare out to me are [1] your atmosphere vented BOV, it's well documented that our ecu's prefer a recirculation valve as they need to account for the blown-off air. and [2] the cams - i'm not sure if the different cam will change the expected vacc at idle? but it seems likely that a cam install issue would lead to a misfire reading by the ecu. a vacc leak would not cause a misfire.

taking care of the DV / BOV issue this week.....

other users with the same cams have no reported problems

[iin10ded]

im not saying the cams themselves are the problem [but i'm not saying they're not - do the other users have the EXACT same setup as you?]. i was thinking that it may be related to an install problem? something not done correctly?

changing cams is an involved process, if something wasn't done correctly i can see a timing issue.

[rottb5]

a vacc leak would not cause a misfire.

Actually, a vacuum leak will cause a misfire.

The problem is either a vacuum leak or the timing set incorrectly.

Sucks that you threw so many parts at the car w/o fixing it.

Good luck!

[EOD-5]

btw compression is at 185 on all 4 cyls

the light went off for half of yesterday and then back on...this sucks! ha