Hey Art,

The sensitive AMM/ECU relationship was impressed upon me a little over a year ago, when my '90 suddenly lost power, seemed to be running lean, and set the check engine light. Still pretty drivable with the 5-spd. Next morning I checked the codes: 1-1-3 and 2-3-1, IIRC. I scoured the BrickBoard for similar tales of woe. Thought I had it narrowed down to the intake hose (indeed there was a hole).

With only on-street parking, cold weather and a very grumpy 9 to 5 meter-maid, I had to get the car going in short order. Got a replacement intake hose and a fuel pressure regulator (just in case, being within the failure bracket I figured why not deal with it now?). For installing the FPR, I disconnected the battery. Got it all together again. Started the car and it would stumble and stall. If I opened the throttle by hand I could coax it to barely run. Few ginormous pops in the exhaust. Seemed it went from running lean to super rich! I tried all sorts of iterations of things, and had to admit defeat that day when the sun went down at 4:00pm. Next day it hit me to try the unplug-the-AMM trick. I did and it started and idled well enough for me to roll the car a few feet back and forth over the next few days to hide the meter-maid's daily chalk mark on the front tire while I waited for a used AMM to come in the mail. Replug the old AMM in, and it would run like crap. Unplug it and it would idle. When the car warmed up the engine tone would suddenly change for the better, and the exhaust would go from stinky to not so stinky. To me this said the fuel injection was going closed-loop and that the O2 sensor was at least functioning "well-enough".

With the new used AMM, everything was healthy and good again. What I think happened is that the original problem was not so much the hole in the intake hose (it wasn't helping, but it had clearly been lurking a long time), but it was that the AMM was hopelessly out of spec, but it died slow enough for the ECU to adapt until it reached a threshold, then then the CEL illuminated. When I disconnected the battery to install the FPR, the ECU was cleared, and then it couldn't figure out how to cope with the bad AMM. If it happens slow enough, it seems that these ECU's can adapt to AMM's that are beyond dead.

-Ryan
--
--------------------------
Athens, Ohio
1990 245 DL 133k M47, E-codes, bunch of fun accessories
1991 745 GL 290k (Girlfriend-mobile)
Buckeye Volvo Club