1989 740T Trouble diagnosing engine problem

blacktooth · Post by **blacktooth** » 27 Jun 2011, 11:59

I bought an 89 740 Turbo about a year ago as a cheap second car that became my daily driver when my wife took on a new job. It ran great until earlier this year. While sitting at a red light, it started idling really rough, and I was able to crawl into a parking lot, where the car died. It will start and idle very rough, and occasionally die. It will die as soon as I try to put it in gear. I'm at my wit's end, as my knowledge of this car is minimal at best.

I've checked the fuel pump relay and it seems to be good. Tested the injectors, and they all pulse and spray patterns all look identical. All spark plugs are firing. the 1st and 2nd plugs are alot cleaner than the 3rd and 4th. If I pull the 1st and 2nd plug wires while car is idling, there is no change in the idle. But if I pull the 3rd and 4th wires, the car immediately dies.

I am trying to get my hands on a fuel pressure test guage. Where would I put the guage to test the pressure? Between fuel line and rail?

I can hear the main fuel pump when I turn the key into the on position, but have a hard time listening for the pre-pump. Is there any way to test that pump?

Thank you in advance of any guidance anyone can give. I love this car, and am doing my best to learn everything I can about it.

Post by **billofdurham** » 27 Jun 2011, 12:24

It would appear that plugs 1 and 2 aren't doing the job they are paid for. Pulling any plug should change the idle. When you tested the plugs did you get a good spark from these two? How good are the plug leads and are they touching metal anywhere?

The only way to test the in-tank pump in-situ is to run a jumper wire to it. This isn't too difficult because it is accessed through a hole in the luggage area floor.

Bill.

bugeye58 · Post by **bugeye58** » 07 Jul 2011, 09:05

I hate it when the original poster leaves us hanging on a problem!