My car will sometimes start, but not run long. Fuel pump primes for brief 1/2 second after turning on ignition. Car starts after cycling key 4-5 times -- measuring the fuel pressure shows it about 40psi. Car runs but dies in a few minutes. Measuring fuel pressure during engine on shows pressure dropping, car dies at ~5-10psi. Found that fuel pump is only on during first 1/2 second, then never comes on again. Shorted around fuel pump relay and fuel pump stays on -- car runs fine when jumpered, stops after removing jumper. Fuel pump relay does not stay on for some reason. ECU is telling the relay to energize but something is causing relay to turn off. Measured output of ECU with scope and see some sort of pulsing signal, seems to change slightly after 1/2 second. There are no fault codes nor ODB scan codes. With the work I've done so far I've eliminated the fuel pump, filter, fuel regulator, ignition, TPS, MAF sensor, and the wiring between all these and the ECU.

Question: fuel pump relay? ECU? Or some other signal feeding ECU? I've read about some safety switch (rollover) for crash safety. How does this control the relay?
(email replies ok)

I seemed to have put this in the wrong forum. Admin, can you move this to the 850 Forum? Thanks.

:00000732: again :grin:

Moved it for u

relay, common problem. volvo ones are only good for 12-17 years.

Sounds like a MAF Sensor problem to me... especially since it starts only for a few minutes. If you have problems with stalling (on the road or something) then I'd prolly go for something else...

Thanks for the feedback folks.

I had previously checked the MAF sensor but found all the voltages correct. There were no fault codes indicating this either.

I suspected the fuel pump "controller" but didn't know for sure. Someone suggested taking it apart. I did this and found a small circuit board, a few transistors, resistors, caps, etc. a relay (duh!) and a small IC. The whole circuit needs pulses from the RPM sensor to keep the relay engaged. I had measured the input to the controller and saw the RPM spikes so I knew (mostly) that the ECU was sending the right signal. At least for the first key on time.

I also found about 10 bad solder joints. After resoldering these I reinstalled and turned the key on. The car and pump sounded different. I crankup up the car, and put my ear to the fuel pump. IT WAS WORKING. I saved a bunch of money on this fix ($50), but it took my about 3 weeks to find it (working a bit here and there).

Hope my posts can help someone on their fuel pump problem.

That's a good work done!

A new fuel pump would cost us here slightly less than RM2K! For around that less a cost, it was great job! :thumbsup:

I see that you're handy with machines and stuff. That's neat. :)

Thanks. If I ever have an ECU that goes bad (and forces me to get another) I will try the solder trick first before putting out my money for a new/used one. I hate paying a dealer/shop to fix the problem. I sometimes pay them to trouble shoot it, then I do the fixing.

I ran over a rock and put a hole in the oil pan on one of my other cars. Dealer wanted $1000USD to fix (with 8 hrs of labor). I used the labor charge, x 3, with a welding unit -- me and a friend did the work in about 3 days (part time) and 4 pizzas. Pretty "free" in that sense.

:thumbsup: Papa John...

Feel free to share your experience, in a new thread prefereably!
:)