To give some back ground (the complete post is at the bottom) my 90 744ti was making a high pitched wine that I traced to the rear fuel pump. When I pulled it the negative terminal for the pump was disconnected and the connector it plugged into was black. After I replaced it the car ran for about ten minutes and started sputtering. I then replaced the FPR and the results were about the same. I then replaced the main pump and everything was great for about two weeks. Yesterday on my way home I noticed that my main pump was starting to make the same strange grinding buzzing sound and I am needless to say quite frustrated to say the least. During my attempt at fixing this problem I did check what I thought was the in tank pump ground but not the main pump ground. Can anyone tell where the two grounds are located and does this sound like the problem?
Thanks.



From part one
"Several weeks ago I noticed a whine in my 90 744ti that I traced to the in-tank fuel pump as it went away when fuse 11 was pulled. Before I was able to switch out the pump the whine would become a growl after 20 to 30 minutes of driving. I just finished installing the new pump but the whine and hesitation and bad idle are still there. I know the old pump was faulty because the ground connection was separated from the pump when I pulled it and the plastic portion of the pump where it connects was very black. Kind a scary considering where is located. I read in the FAQ that the pump ground could also the same symptom as a bad pump. I checked the only ground located in the trunk but I am not sure if that is the correct one. I will also replace the check valve tomorrow. Does any one have a suggestion?"

Part 2
since then I have replaced the check valve and the fpr and after some initial sputtering from fouled plugs the car was running strong. But after about 15 minutes of spirited driving it fell flat on its face and is parked on the side of the road. It is very hard to start and sputters and backfires and does not have enough power to run. I am thinking bad main fuel pump but at 155.00 I can't afford to just throw money at it.
Help and Thanks.
--
90 744ti, Airbox, K/N, Cold air, G-Valve, Dual boost control, VDO, Modified exhaust. 88 745 gle.

When I arrived home tonight I cleaned both of the grounds in the trunk and drivers kick panel. Neither looked bad but were vigorously cleaned anyway. I also removed and re-soldered the fuel pump relay. I verified that the in tank pump was running by inserting a hose into the fuel filler neck. The main pump comes on when the key is turned on but starts to create a growling (this is not a proper word to describe it) after the engine is cranked. The pump sounds as if it is not receiving fuel because the sound is not constant. I have not changed the fuel filter but it is not that old 10k at the most.
--
90 744ti, Airbox, K/N, Cold air, G-Valve, Dual boost control, VDO, Modified exhaust. 88 745 gle.

Testing the 240 fuel pumps is a breeze (by jumpering 2 fuses). Not so easy on the 700, but here's what I would do...

1) Disconnect the fuel line at the injector rail and route it into a safe container. (Skip this step if you just want to hear the pump run.)

2) Remove Intank pump Fuse 11 and improvise a jumper wire to apply voltage to the Fuse 11 terminal that is farthest away from you, i.e., toward the engine.

You can get battery voltage from the Fuse 1 terminal closest to you, after removing the fuse. Use a jumper wire with a flat male terminal on each end to take the voltage voltage from F1 to F11.

The Intank pump should push a good flow of fuel (thru the unpowered Main pump) all the way to the injector rail.

To run/test the Main pump, jumper voltage to the other F11 terminal, the closest one.

NOTE: This is from a '93 Green Book wiring diagram, which is all I have. It should work for you if Fuse 11 is for your Intank pump.
--
Bruce Young
'93 940-NA (current) — 240s (one V8) — 140s — 122s — since '63.

Does the book list the location of the grounds. I believe both pumps to be good. My concern it that one ground is faulty and putting a strain on the pump.
--
90 744ti, Airbox, K/N, Cold air, G-Valve, Dual boost control, VDO, Modified exhaust. 88 745 gle.

In the '93 book the tank pump ground is under the trunk threshhold cover, on the left side maybe 8" or 10" from the upsweep.

The main pump ground runs to a "ground collection rail in el. distribution unit" (fuse/relay block?) and then to a grounding block that appears to be down low behind the right front kick panel.
--
Bruce Young
'93 940-NA (current) — 240s (one V8) — 140s — 122s — since '63.

Thanks.
--
90 744ti, Airbox, K/N, Cold air, G-Valve, Dual boost control, VDO, Modified exhaust. 88 745 gle.

Checked the fuel pump relay yet?
--
David Hunter

I gave it a visual inspection and did not notice any cracks. I will swap it with my 88 745 just to see.
--
90 744ti, Airbox, K/N, Cold air, G-Valve, Dual boost control, VDO, Modified exhaust. 88 745 gle.