QuestionQUESTION: Jan, what sensors will the ECM "read" when the car is cold and in open loop? MAF, ECT, IAT, MAP, Throttle body module inputs (position), and ???? Are these correct? And what else sends info to the computer?
I've got a 98 A4 1.8TQ with 108K that ONLY acts up if I decide to drive off just after cranking it up COLD. If I wait a couple of minutes for it to go into closed loop, then it'll drive without ANY problems the rest of day (at least until it's cooled down enough to be in open loop, again).
The acting up will generate misfire codes (0300 through 0304).
Thus far, I've replaced plugs (OEM, then Denso, the Autolite platinums, now back to new Bosch (OEM)), all four coils, Coolant Sensor (twice, to make sure that I didn't get a bad new one), replaced the ECM with a known good one, and replaced the POS (ICM).
The MAF works the same whether it's unplugged or connected. The IAT reads ambient temperature before starting and warms up accordingly with a closed hood. The latest ECT reads near ambient and warms up linearly to around 100*C. The fuel pressue was about 55psi (60psi with vac removed).
Again, if I let it warm up for a few minutes without cracking the throttle (Oh, also replaced the TB module, too--did TBA at least a dozen times throughout this ordeal), the car will run fine - all the way to redline without a hiccup or ping.
Lastly, I've done a leak check and there's no leaks. Compression is 180-188 across the board.
Any ideas? I'd be happy to hear them.
ANSWER: Wow you have gotten into this problem at great depth. In the warm up stages a number of the sensors are not used, but there is an enrichment setting for the fuel metering and also there is something regarding less advance on the distributor. I cannot remember exactly, but it may be worth checking the hall sensor on the distributor; this may be the problem. I will also ask my buddy who worked on a car with me that had a similar problem, let me know if the distributor could be the issue. Jan
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QUESTION: Jan, it's a coil-on-plug design without a distributor. It's the AEB 1.8T engine. Any other ideas? Thanks in advance!
ANSWER: Oops I should have known that. The crank sensor is what is used to determine timing etc, so it's possible that the crank sensor is flaky when cold, although not likely. Any DTC codes?
Jan
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QUESTION: Only the random misfire code (16684 (P0300)) and another or all misfire codes (16685-88 (P0301-0304)). At first, I swapped the coils around trying to chase a presumed bad one. But, opted to just replace them all (including new coil boots). I've checked the wiring to the cam and crank sensors and they're in good condition.
Still got my mind open, any thing that I might be missing before I just start throwing more parts at it?
AnswerIn my opinion throwing parts at this problem and at this stage is an expensive way to get even more of a headache...; you have already replaced all the parts it can be. I would suggest going to the ground wire which comes from the coil packs, and verifying a real good connection to the block. Also check the integrity of this wire.
Then check the engine fuse 232 which is a 20A, supplies power to the coil packs. Make sure that the fuse is nice and tight, and that the connections on the back of this are good. Let me know, Jan
