1991 740 No start-up....Everything tried

mojoe28613 · Post by **mojoe28613** » 26 Feb 2014, 14:39

OK..............I am at my wits end....I have read every no start forum article and traced everything and I am totally perplexed. I consider myself to be an expert back yard mechanic but this is really messing with me. It is a 1991 740 wagon with 149000 miles.....in magnificent shape. I bought it from a guy not running who, like myself had lost all patience with it.....It was running fine for his wife one day then ...bam...dead...he got it running for a couple blocks and then bam....dead again........here's the rundown:

1) Fuel pressure is great at 10 plus pounds
2) Spark to the plugs
3) relays good (tested)
4) IAC valve good (tested)

What next..........I am trying to figure out best way to test injection system.........

Thanks,
mojoe

lummert · Post by **lummert** » 26 Feb 2014, 15:19

10 plus psi of fuel pressure is not a good fuel test. Need a more accurate fuel pressure test. But, 10 psi is not enough pressure.

mojoe28613 · Post by **mojoe28613** » 26 Feb 2014, 18:29

Yeah....my fuel pressure gauge didn't go any higher, but it pegged it HARD.......Fairly sure the fuel pressure is good.......new fuel pump was dropped in tank. I'm beginning to think along the lines of the ECU being bad.....

Thanks,
mojoe

klar5020 · Post by **klar5020** » 11 Mar 2014, 07:56

If you haven't fixed it yet.. I had the same problem. Found the RPM sensor bad... On top of the transmission bell housing.. blew me away. It would run for a while then quit.. Everything else was good..

Hope it helps...

Larry

mojoe28613 · Post by **mojoe28613** » 22 Mar 2014, 14:19

Well.......She's still sitting in the same spot in the shop.......I think I have finally figured it is something to do with the injectors.....How can I tell if they are pulsing when I'm trying to start the car......started to pull the fuel rail but seems like there would be an easier way....

Thanks,
joe

Ethan Rode · Post by **Ethan Rode** » 23 Mar 2014, 02:22

You could use a noid light to make sure that the injectors are getting signal from the ECU. I usually rest a long screwdriver against each injector, as a kind of stethoscope. That is more helpful in diagnosing power balance problems, though. It's unlikely that all the injectors are bad.

lummert · Post by **lummert** » 23 Mar 2014, 08:28

Radio interference suppression relay?

Post by **rgk** » 23 Mar 2014, 14:18

You can rent a fuel pressure gauge from an auto parts store. If your gauge does not go above ten psi, then it is likely not a real fuel pressure gauge.

mojoe28613 · Post by **mojoe28613** » 25 Mar 2014, 12:38

Yep......I tried the Radio suppression relay swap and nothing....

I did get it to bump fire on starter fluid........

One evening this week I am going to see if I can hear the injectors firing........

Post by **regent** » 25 Mar 2014, 16:57

Have you physically checked the positive supply voltage to the injectors with a volt meter or test light?
You should see close to Battery voltage on all injectors with reference to negative/chassis (while the ingnition is turned on and the motor is still).

On a running engine, "pulsing" is done by switching the negative on/off.
The only way for all injectors to play "bad" is absence of +12 V.