740 starts,idles,falters,recovers,repeat

ccb222 · Post by **ccb222** » 15 Jun 2009, 08:48

'87 740 starts, idles smoothly at 1,000 rpm for about 20 seconds then slows to 750 rpm, falters, and sometimes recovers to smooth idle at 1,000 rpm for 20 secs, etcetera. It always ends up stalling out. The greatest number of "recoveries" I've been able to experience is 7.
This behaviour was intermittent in the past, but now the car can't be driven.
I have replaced both fuel pumps and filters and the behaviour hasn't markedly changed.
Chilton's fuel system troubleshooting page doesn't exactly describe this, so don't know what to do.
Any ideas??
Thanks, CCB222

Post by **billofdurham** » 15 Jun 2009, 12:33

Erratic idle:
Check air intake system for leaks.
Check fuel injectors.
Check air control valve hoses for proper connections or blockages.
Check throttle valve adjustment.

Bill.

ccb222 · Post by **ccb222** » 15 Jun 2009, 15:51

Thanks, Bill, I'll checkeverything on the list.
In the interim, I have discovered some "patching goop" on the front facing outlet of the fuel pressure regulator on the fuel rail, so I suspect it as a problem. Also, does a fuel pump relay die quickly or does it fail over time? Just ideas I've generated by reading MVS posts and wonder if these thoughts have any merit. CCB222

Post by **billofdurham** » 16 Jun 2009, 11:53

does a fuel pump relay die quickly or does it fail over time?

The relay does wear out over time but it will usually just stop when it has had enough - it gives very little warning. However, we have found some relays, including that for the fuel pump, will come to life again, albeit for a short time, if they are given a hard flick with the finger. It is sometimes enough to get the car home.

Bill.

ccb222 · Post by **ccb222** » 17 Jun 2009, 18:12

I have now replaced the injectors (used, because I had them) the fuel pressure regulator (used because cheap) and the relay (used also). The car IDLES nicely, most of the time, but it will not accelerate smoothly, and there's no power. I've disconnected the Air Mass Meter and the idle increases, which is contrary to KMANIAC's advice that if bad, the idle will decrease in revs, so I don't know what conclusion to draw. I just read KMANIAC's write-up re: the crank pulley and its propensity to fail when old which is possible in this case, but then, everything I read immediately becomes THE problem. Total confusion and frustration here, but DETERMINED! All comments DO HELP, and THANKS for them! CCB222

ccb222 · Post by **ccb222** » 19 Jun 2009, 20:00

Car is running, after I followed the route of many others and replaced the Air Mass Meter. However, it's not perfect. The problem now is DIFFICULT HOT START. This, I can live with if I must, but would love a solution. I shall read the posts but in the meantime, all suggestions welcome. Thanks, ccb222