backdoc

posted a thread about my check engine light coming on last week. Started the car and the engine was running and idling very rough. Some people said put Techron in. I did and it was still running very rough. Got the VAG-COM in today and pulled the codes. The check engine was flashing by the way. The codes are as follows:
5 faults found:
16705-Engine speed sensor(G28)-Implausible signal
P0321-35-10 Intermittant

16684- Random multiple cylinder misfire
P0300-35-00

16686-Cylinder 2 misfire
P0302-35-00
The last two faults were indicated twice. I have a 97A8Q.Thanks in advance for the help. I also have the Bentley. Can't wait to get the car running so I can play with the VAG-COM.
Doug G.

PaulW

If so, which ones came back?

Sven_S8

The last codes point towards injectors, or coilpacks / sparkplugs.

Is there a procedure in Bentley to (electrically) test the injectors?

-------------------------------------------------
<i>Electrical checks on injectors

- Remove connector from the injector which is to be tested.
- Connect hand-held multimeter to injector to measure the resistance.

Specified value: 13...16

</i>
-------------------------------------------------


But as Paul says, see which codes come back first.

PaulW

But we've had these codes before....the ones for the misfires....and it has either been a bad power stage (the thing that fires the coil pack, it gets a small signal from the ECU and makes a big 12 VDC signal to fire the coilpack) or it's a bad injector, usually dirty and a can of Techron cleans it up.

But the other one does not normally show up.....that's why I asked if it came back.

Sven_S8

You think it's ECU related?

PaulW

No

backdoc

no i did not clear them. Is that what i should do and see what codes come back?
Doug G.

backdoc

Disregard my latest post. I just went out and cleard the codes. Started the car up waited for the check engine light to come on and it did and was flashing. Pulled the codes again and got the Random multiple cylinder misfire 16684,
and cylinder 2 misfire 16686. I can't imagine it's the ECU, it had the ECU replaced 3 years ago. I tried Techron, and it didn't work. Thanks
Doug G.
97 A8 4.2

PaulW

If so, you need to go to the fault code and follow the troubleshooting procedure.

If you don't have it.....you need to do this and report back....it's a lot of typing, we've discussed this before.....

Using vag-com, plug into the car, then go to engine. Go to measuring blocks, and then go to channel 19 and 20, put them up on your screen.

Start the car and then let it run for a while, it's showing misfires per 1000 reveloutions....should be no more than 5.

Measuring block 19 is showing cylinder 1, 2, 3 and 4, measuring block 20 is showing 5, 6, 7, 8.

If you have misfires on 1-4-6-7 or 2-3-5-8, then it's your power output stage.

If it's just on one cylinder, note it down.

Then take the cover off just above the air filter, the black one.

You'll see wires attached to the two power output stages. Wires come in from the ECU and go out to the coil packs.

Disconnect them and swap them.

Reconnect.

Then start your car, go to the measuirng blocks again and see if the misfire is still in the same place.

If it swapped to another cylinder, then it's one of your power output stages, if it's on the same cylinder, it's probably a clogged injector.

Good luck, keep us posted.

pw

backdoc

Yes I do have the Bentley manual. I will follow your procedure and post the findings. Thanks a lot. The VAG-COM is very cool.
Doug G.