Bebee

The cylinder 1 misfire saga continues....

Ive been trying to stumble my way through the Bentley - this manual leaves alot to be desired; after having relied on Bentley manuals for years with VW's, the explanations of procedures for the A8 are vague at best.

I bit the bullet and ordered two new POS's which should be here on Wednesday...I'm just throwing $$ to the wind at this point, hoping that a random part will fix the issue - I'm far enough into it that my pride is keeping me from just dropping the car at a mechanic.

I ran through the POS tests this morning and found that each terminal of the POS is functioning as it should (according to Bentley), however, the test to check the signal coming from the ECU failed on all terminals. (no lights whatsoever) - but the car runs, albeit with a miss, so I can only assume that the Bentley has provided me with some gross misinformation...or my ECU is friggled.

This test failed on all counts:

Connect one terminal of voltage test lamp to engine Ground (GND), test terminals 1, 2, 4 as well as 5 in sequence on both 5-pin connectors using other terminal.
Operate starter for a few seconds during each test.
During this, voltage test lamp must blink respectively.
If voltage test lamp does not blink.
Connect V.A.G 1598/19 test box to wiring harness for Engine Control Module (ECM) => page AUDI-D3-FU02-ST-001-03ST-7.

But this one passed:

Both 5-pin connectors remain connected to power output stages.
Disconnect both 4-pin connectors from power output stages.
Connect voltage test lamp between B+ (e.g. from a connector of an ignition coil terminal 15) as well as respectively to a terminal on 4-pin output of power output stage.
Note:
Voltage test lamps with very low current draw glow already when engine is not running and become lighter and darker while engine is being started.
Operate starter for a few seconds during each test.
During this, voltage test lamp must blink respectively.
If voltage test lamp does not blink at one or more outputs, replace power output stage.

Does that make any sense at all?

Next, I pulled the power coupling from injector #1 - it passed both electrical tests (resistance/power w/ ignition on) When I put it all back together, the car wouldn't stay running and threw a crapload of CEL codes. There were injector malfunctions on cylinders 1, 4, 5 and 8; the Idle control valve threw a code, and I had misfires on all cylinders. Furthermore, there was a metallic squeal from the front of the engine.

I spoke a few choice words and retired from the shop for lunch. When I returned, I cleared the codes and tried to start the car again. This time it fired and continued running. It immediately threw the cylinder 1 misfire again, but has yet to throw any other codes.

If you're still reading this, my question is this:

Is it normal to have a bunch of wacked codes thrown when performing these test functions?...or is the possibility of a friggled ECU even higher now?

KYNZ

might want to check your timing belt...mine was off a tooth and it was the root of all my evil

Bebee

Will checking the timing belt require dismantling the entire front end of the car, or is there a much simpler way to determine?

I've also got a burning question...

How does the car know that a particular cylinder is misfiring? I only see two knock sensors listed. Could a failing/loose knock sensor force a misfire?

PaulW

However, does the car stumble on 7 cylinders when running properly?

If so, there is a very good chance that it's either a coil pack at cylinder 1 gone bad or a power output stage.

Did you swap cylinder 1 coil pack with another cylinder to see if the misfire swapped? If not, do that, clear the codes, start the car and see if the misfire swapped.

Did you swap POS' with each other and see if the misfire swapped? If not, swap the POS positions, clear the codes, start engine, and see what cylinder now has the misfire.

If it did swap, then you found your cultprit. I don't know how it determines the misfire.

Lastly, make sure you get injector cleaner and put it in your tank, you could also have a mechanically stuck injector. When I did some serious troubleshooting on a 3.7 once, it ended up being a stuck injector that remedied itself over a week long period of running on 7 cylinders after a few bottles of injector cleaner. Or you might need a new injector and replacement o-rings. I would try the cleaner first.

Good luck, take a break for the rest of the day if you can, try not to think about it too much tonight and get back in there in the morning!

Happy New Year! I'm leaving for my party!

pw

gondar

signal, and,it were loose (mechanically)I suppose it would be less likely to kick in.

I think an out of register TB would affect all cyls, though the "deviant" might show up first.

Swap a few parts back and forth, or invest in a new coilpack to experiment. I had one fail (2000), w/o warning, and it wasn't even hot outside. Might be good to have a spare.

Always Overcharged

plug and finally output stages does not shift the fault. And if the fault follows any of these then whatever one it follows is the issue.
If still # one on all shifts and the test on the ECU wires did not work then try swapping the ECU.

You may have earthed out the injector circuit so check fuse if there is a problem there.
Follow the manuals accurately first and if no result then look outside the square.
Be methodical and dont let it rattle you
Good luck

Always Overcharged

oh and if you need Elsawin docs please email with what you need

Bebee

What are Elsawin docs?

Always Overcharged

Elsa win is a work shop manual that is used by Audi themselves

hillpc

I know this is an old thread, but it may still help someone. The misfiring cylinder is identified through the rpm sensor. The ECM expects a quick "jolt" in rpm just after each cylinder fires. If it doesn't see this, it flags the cylinder that was just fired. Damn, it's quick! Pretty impressive.