94 Transport Will not start

[LMP]

Originally Posted by gordobw

I will check again, it is my third pump. Now I was also told if there is not enough OIL pressure, the fuel pump will not kick on is this correct?

The fuel pump is normally triggered on for 1 second with injector ON at the time the key is turned to on. then it stays dead until the engine is started . The oil pressure will ALSO switch the fuel pump ON as a back up circuit.

[Jim Adams]

fast way to check pressure is on the passenger side above the oil filter there is a little sensor sticking out ,,this is your oil pressure sensor,,if you take out the sensor and crank engine and oil spits out then it is pumping you should also be able to spin the engine over for about 40 seconds let go of the key and see the oil gauge move slightly but sure way is to take out the sensor and crank it over,,is it has a big sensor and four wires or more than 2 there is a low oil pressure cut off switch but I dont beleive you have that set up,,also try to check the wires going to the fuel pump and see if there is juice to the pump when cranking over another thing does your igntion key have a little metal chip in it?? if so the chip may be bad and will not allow the cars security to override and start,,,some GM,s have a chip in the key it is coded for security.

[stevenjames]

Have you found out anything useful?

My 94 trans sport 3.8 just died in the same way you described ("running perfect but then just completely died"). I am a little luckier because it started up again after waiting 5-10 minutes. Problem is, it has occurred some more since. My local mechanic spent a long time checking many aspects, all showed OK (fuel pump pressure, fuel filter, back pressure, cam and crank sensor, Ignition Control Module). They narrowed it down to losing injector pulse and suspect the PCM, but could not test this. Checked injectors and circuit for resistance and short to ground--OK, and does not lose spark or power to injectors.

[gordobw]

I still have not fixed my problem, I have now changed out the EGR (What a Pain) I guess I will look into the PCM

[gordobw]

I have been told that I may have a bad ground from the fuel pump, where is the ground? I do not see an additional line coming off the pump.

[NiteOwl]

There is a real easy test for the fuel pump on most GMs, the fuel pump test connector.

Using a fused (10 amp) wire connected to B+ (12V), and with the key off, apply power to the connector and the fuel pump should run. SIMPLE !!!

On the 3.1 look for a loose female connector with a red wire coming out of the wiring harness near the MAP sensor.

Power for the fuel pump is supplied by two circuits.

The primary circuit is the fuel pump relay controlled by the ECM.
Upon key on the ECM activates the fuel pump relay. As long as the ECM receives ignition reference pulse (engine cranking or running) it will power the relay. If there is no reference pulse then the ECM will shut the relay down within 2 seconds of key ON.

A backup circuit uses the oil pressure switch. When oil pressure is above 4 psi a switch closes, bypassing the fuel pump relay and supplying 12V to the fuel pump. This is a separate circuit from the oil pressure indicator.

All of this is straight out of the GM service manual for the 94 trans sport

With no fuel rail or valve to attach a fuel pressure gage, measuring fuel pressure is a bit of a challange on this engine. GM uses a special adaptor

The wiring diagram shows that for the fuel pump 12V is supplied by a grey wire (.8 GRY) and ground is provided by a black wire (.8 BLK)


Hope this helps

[LMP]

www.avigex.ca/xport/fuelcontrol31.jpg
As suggested before, DO feed the pump direct with 12V to make sure this is the problem. It will either run or not, and if the pump runs, then the engine should start...if you actually have a problem with running the pump. YOu must clear options one at a time.

If engine does not start with pump ON, look into the throttle body to see if you have fuel sprayed when someone else turns the ignition ON. If not, disconnect the body throttle injector and check for 12V to show for 1 o 2 second when turning the ignition ON. I have seen failed throttle body injector ...however there are 2 on this one and having the 2 fail at same time would be bizarre... unless one was alrady failed and the second just failed now...you would probably have noticed problems before....But better check for that 12V pulse anyway.

[gordobw]

I have found out the problem......It was a bad wire in the wiring harness, I repurchased another wiring harness, and it works fine now

[stevenjames]

Thanks for posting your solution...I wish it was going to be something I could use for my intermittent problem, but I am guessing not...What is the "wiring harness"? Associated with the electrical to/from the fuel pump?