jeffkruse

about a week ago sometimes during acceleration my 2004 Audi A8 4.2 was hesitating/missing. Then it went away for a week. Well now it came back, and this time is was so bad that the engine just stop. Tried to restart and it would not. I had to push the car into a lot. Then it restarted. Put it on the vagcom and 16689 and 16690 misfire 5 and 6 cylinder codes displayed. Cleared codes and drove for about 10 miles, now it still misses but have yet not to get a error code yet. Had people tell me different parts to replace but want to make sure I replace the culprit. Please any help would be appreciated.

Thanks,
Frustrated

MP4.2+6.0

The usual. Plugs/coils/maybe some of both.

If last tune up more than 35 or 40K miles ago or you don't really know service history, I would just do all of the plugs as the normal likely. Plug long term change interval is every 60K miles on a 4.2 (55K for first interval, then every 60K) to be clear, but in presence of issues later in service life, I just change them.

Std. coil check is to move them to other locations (like 7 and 8) and see if error follows coil packs or stays at plugs. Many Audis had coil pack recalls, so you could check if yours was done. I got 12 new ones on the W12 even w/ no issues ever; different coil back than 4.2's though. There is a small sticker under hood if not worn off, or try your VIN here: Audi Recall Services by Vehicle Identification Number

jeffkruse

UPDATE: I just ran out to get some NGK Double platinum plugs and no issues what so ever, ran excellent. So i think this issue only rears it's ugly head is when the engine is warm. Don't know if that makes any difference. Also just found a service bill. Plugs were changed 8,000 miles ago Autolite XP Iridium.

richard-tx

I think the issue was Autolite. NGK plugs is what Audi specified. I think the lesson learned is to use what Audi recommends and accept no substitutes.

jeffkruse

I drove around for about 10-15 minutes and logged Channels 015-016-017 in the measuring blocks 08 of the engine module01. This excel spread sheet had over 3700 entries but most had all zeros. So I removed everything that did not have any misfires. Most are on just one cylinder at a time. Not sure if this means anything or if someone can look and say it is not this etc......... I cannot get any misfire DTC's But it is misfiring. Plugs were installed 8000 miles ago. Thanks in advance for all your help. Attached is the excel spreadsheet. Sorry if you scroll to the bottom it will give you the total of times it misfired in the 15 minute period

MP4.2+6.0

I'm not big on reloading csv files, but meantime I'm not clear on whether you changed back to the OE NGK's, or if you still have the Autolites in there. You mentioned again in the latest post the plugs were in there for 8,000 miles, which seems inconsistent w/ getting NGK's just days ago after earlier saying the Autolites had 8K miles ? If new NGK, then an issue elsewhere of course.

Also, when I go back to your first post and then think about misfiring, you mentioned car didn't start at one point. Causes me to think about the crankshaft position sensor, where people report it often begins w/ hot starting issues; could fit misfiring if it misses the crank signal momentarily. See if Mister Bally or someone with experience there can comment, or even better search for prior posts, diagnostics and comments about it. I don't know what codes the crank sensor starting to fail puts out, since I have never had the issue.

TSHong

I agree with MP on the plugs and coils. If you had an issue with just a couple of coils, it would not die and prevent you from starting your car. You might have multiple issues but I would start by switching those coils with another cylinder to see if it misfire followed the coils.

jeffkruse

I bought NGK plugs thinking that was the problem, when I got home I found a service invoice from the previous owner and he put the autolite plugs in 8000 miles ago, so I did not replace the plugs yet figuring it was not them because they were replaced recently. Also because there numerous misfires in 6 of the 8 cylinders all plugs would not be bad. In a 15 minute driving period,
Cylinder 1 - 32 misfires
Cylinder 2 - 127 misfires
Cylinder 3 - 0 misfires
Cylinder 4 - 0 misfires
Cylinder 5 - 151 misfires
Cylinder 6 - 246 misfires
Cylinder 7 - 204 misfires
Cylinder 8 - 109 misfires

Mister Bally

Incorrect spark plugs can cause the engine controller to try to compensate and trigger fault codes. Be sure you are using specified plugs for your car. Best to get from an Audi dealer. I get Bosch because that's what came with my early '04 with 4.2 L engine. Only plugs listed in the owner's manual are NGK or Bosch.
When you buy from a dealer, they have an Audi logo on the insulator and are packaged in a VW/Audi carton.

jeffkruse

This is the only DTC in the Engine Module.

17981 - Left Engine Mount Solenoid Valve (N144): Open Circuit