Pmulls870

I've been chasing around a misfire as best I can with some help from google and existing threads but I can't seem to find the info I am looking for. I'm hoping someone might be able to help me out.

1st problem: Check engine light, smelled gas in the cab, I had lean run codes for both bank. I replaced the gas cap with an OEM model and the issue went away.

2nd problem: Misfire at low RPM below 40mph and only when the engine is hot. Codes are cylinder 5 miss, cylinder 6 miss, and a random miss. I believe the random miss code defines when the miss occurs and is not related to what cylinder is missing. Please correct me if I am wrong.

Steps taken:
1. pulled spark plugs, verified no oil residue, corrected a gap issue at cylinder #1. Car started, codes cleared, all codes returned.
2. Pulled plug wires, inspected for cracks and protrusion, none present. Tested for amp loads, no leaking detected. Wires reinstalled, codes cleared, codes returned.
3. Inspected coil packs for issues, no issues seen on coil packs, tested with a light water mist on coil packs looking for arcing. No arcing noticed in dark garage. Coil pack for #5 and #6 pulled, swapped into #3 #4 coil pack position. Codes cleared, #5 and #6 misfire code did not return, random misfire code still present.
4. Coil pack for cylinder 5 and 6 replaced with dealer replacement part and buttoned up. Cylinder 5 code still present cylinder 6 code gone, random misfire still present.
5. Coolant temp sensor pulled and bench tested. Test is good. Coolant temp sensor reinstalled, codes cleared, cylinder 5 misfire returned, random misfire returned.
6. compression test performed. All cylinders in spec.

I don't know where to go from here. I have to be missing something I just don't know what. I am a complete newbie to this engine platform and gas engines in general, I'm a diesel guy.

Thank you in advance for any insights

Prospeeder

Sounds like it has an air leak. Makes sense because its richer when cold masking the issue. I doubt the gas cap fixed any lean fuel trim codes. It takes quite abit of driving and trip cycles to finally set the lean mixture code. Misfires will come back as soon as they are detected.

Im sure its still lean, using a scan tool monitor live data, and specifically o2 sensor control. It should be a percentage. + is adding fuel for a lean condition, - is pulling fuel for a rich one. Clear faults, this resets the adaption for the o2 control, and it should show you what its really at, anything + or - 15 will set a fault code. You can now use brake cleaner to spray around areas and watch for the fuel trim to wildly change from adding fuel to subtracting fuel when the leak is found.

Pmulls870

Prospeeder,
From the time I first smelled gas in the cab it was about 600 miles (my weekly commute) and at least 15 ignition cycles to set the light. Since the gas cap has been replaced I have put on about 2400 miles and it has had at least 100+ ignition cycles without the light. Would this make any difference?

I will run a live data screen for the next week to create a better picture. I plan to follow 02 sensor data, rpm, speed, and engine temp. Is there anything else I should trace?

This brings another question. I have a scanner with live data capabilities that works well on my trucks. Is there a scanner that works better than any other in the Audi world?

mrk1327

Had a cylinder #6 misfire at low rpm's after months of checking and replacing everything possible ( multible mechanics) turned out to be worn exhaust lifters and cams. Intake side was like new. Easy check by popping the valve cover. keeping it short in case this is of no help.

Pmulls870

it is certainly worth a look. do the valve covers on these engines take a pre formed gasket or do they use a form in place gasket, like a Permatex or something similar?

mrk1327

It's a pre-formed gasket..would use a little perm. on the sharp corners ( you will see what I mean). How many miles are on the engine? If the lifters are cupped even a little worn the cam lobe's are probably rounded which means the valve can't/won't open the whole way causing a low rpm misfire.

Pmulls870

correct me if I am wrong please but I believe that was the case I would be dealing with this issue at all times. If it was a cupped lifter, the misfire should be near constant? I did open up the valve cover and see exactly what you mean though. I will do a little more careful checking tomorrow.

mrk1327

Absolutely NOT and the car can act that way for a long time. If this is a wear issue can be a slow maddening experience.

mrk1327

The 2.8 30 v is a great motor, driving an a4 with 300,000 now but mechanically the weakness is (@high mileage) the exhaust side lifter/cam wear.

Pmulls870

Well I have 198000 miles on now. I think motoracer might be tight. The old girl threw a p1138 and p1136, the lean codes are back. What exactly does the lean code mean? In a diesel it would point me to a fuel filter, the engine is starved for fuel. Is that the case here?