I recently had my 89 740 8V non turbo serviced, i.e. (tune up) at that time my mechanic informed me that the AMM was bad in my car because i was having a hard time getting the thing to start and when it would start it would die so the starting process could take 2-4 minutes for it finally to start and stay running ( hot or cold weather usually first start of day or after sitting for 3 or 4 hr.). He checked the fuel check valve it was fine, but he found that if you disconnected the AMM it would fire right up then let it idle for around 30 seconds and replug in the AMM it would continue to idle and warm to running temp then it was fine to drive. It does however tend to hesitate from a stop when taking off (almost like bogging down like a old carburetor. car with a large fuel dump). then accelerate fine.
I bought this car 5 months and has always started hard it is the same as when I bought it. A couple of days ago my son tried to start the car without doing the AMM trick it started and died a couple times then nothing for days would only crank not start AMM plugged in or not. I checked and replaced the fuel relay, replaced a bad fuel pump fuse. Confirmed that the tank pump worked and the main fuel pump worked. Confirmed fuel to the fuel injector bar, took spare plug using #1 wire confirmed by holding threads next to the block I had spark (spark seemed small to me I no sure how intense it is to be but it did spark across the plug gap). Still no start. Then I pulled the radio suppresser relay on the water res. tank and reseated the connector I also unplugged and reseated the RPM sensor a couple times, and tightened up the power booster thing on the driver side inner fender wall ( it only has one screw in it attaching it to the wall I need to find another) Unplugged the AMM Bingo it started. Still hesitates slightly when accelerating from a standing stop even when warm. I hesitant to drive it because I not confident in its ability to routinely restart.
New Parts: Alternator, timing belt, Fuel pump relay, engine block heat sensor, plugs, RPM sensor papers to be replaced clean cable white band I did not replace it in must have been replaced by privies owner. Idle control value works and has been cleaned, throttle body cleaned, flame trap new.
Question : Is the AMM bad? And if the AMM was bad wouldn't run like crap with the thing plugged in not just have a starting problem? If the AMM is not bad what's going on?
Thanks
Ron