No power to fuel pump. Wiring? Help!

caustad · 12-08-2004

I recently replace my tranny and transfer case but had the car garaged for about a year before I did the work. After I finished it would not start and the fuel pump wasn't getting power. I checked all the fuses and even swapped out the ecu to try another just in case... Still no power. I decided to do a fuel pump rewire and the fuel pump turned on, but the injectors just sprayed wide open and wouldn't shut off. It's not the ECU because it does the same thing with both. I also thought that I might have pinched a wire when I put the tranny back in but I didn't see anything. Any ideas?

**Kracka** · 12-08-2004

Maybe a mouse or rat made a home out of your wiring harness.

520Talon · 12-08-2004

CAS. I had the same problem and it was the Crank angle sensor. It just went after I shut the car off one day.

**Goat Blower** · 12-08-2004

With the ignition on but without the car running, take off your CAS but leave it plugged in. Turn it by hand, you should hear the pump come on for a few seconds. If not, the CAS is bad. If it does, check your MPI relay.

caustad · 12-08-2004

I'll try the CAS thing. I think the MPI relay is good because it clicks when I turn on the ignition. Thanks

FORSFED · 12-08-2004

Just out of curiosity, how does the CAS come into play with the fuel pump turning on? I've got the same issue with my car. After storing it for a year, the pump wouldn't turn on any more so I hardwired it.

12-08-2004

The ecu has control over the fuel pump relay, the ecu energizes the relay for a few seconds when the ecu first powers up to presurize the system and then it will keep the relay on as long as it is recieving a signal from the cas (ie it thinks the car is running). So by doing what Goat Blower suggested you are just telling the ecu the car is running when it really isn't so it should, assuming the cas is working correctly, keep the fuel pump turned on, pulse the injectors, and fire the coils without having to actually be cranking the engine

Edit: Also, make sure you turn it clockwise since thats the way the engine rotates and i'm not sure how the ecu would handle the signals if they were running in the reverse direction...

FORSFED · 12-08-2004

The initial pressurization of the system has nothing to do with the cas though right since the car isn't running? I'm hearing the relay click on when I turn the ignition switch on, but the pump doesn't respond by turning on to pressurize the system as it should.

12-08-2004

The relay is 2 part, it is a relay that clicks on when the key is turned to "run" to tell the ecu to turn on and then after the ecu is on the ecu sends a signal to a differnt trigger wire on the relay and the fuel pump relay section of the relay will then send power to the fuel pump.

And no, the CAS has nothing to do with the initial priming of the fuel system but just because you hear a relay click it doesn't mean its the fuel pump relay. I dont have the pinout for the mpi/fuel pump relay handy but if you could find it you could test if the ecu is sending the signal to the relay to turn on the fuel pump while your turning the cas.

FORSFED · 12-08-2004

I'll have to look it up again. I know that the MPI relay does two things, one of which is turn on the fuel pump to pressurize the system upon key on and the other I don't quite remember. Probably something like you said with turning on the ecu.

Anyway, I don't get that initial prime of the pump nor do I get it to turn on while cranking. The hot wire at the pump shows nothing. From what I'm understanding, this would be an issue with the MPI relay, however I do hear it click...

LightningGSX · 12-08-2004

Have either of you checked for power at the FP check terminal during cranking? Do either of you have the CEL on?

Caustad- What year is your car?

**Goat Blower** · 12-09-2004

Ahh, I forgot about that. There's a check wire on the passenger side firewall for the fuel pump, hotwire that to see if the pump comes on. I remember doing all this same shit about two years ago, it ended up being my injector resistor pack on the firewall.

12-09-2004

You should be able to troubleshoot better with this. If you need any other schematics let me know or if you can get ahold of the "DSM CD" get it, its handy

caustad · 12-09-2004

My car is a 94 tsi and I haven't tried the fuel pump check terminal but did hard wired the fuel pump and you could just hear the injectors constantly spraying wide open when it was hard wired but when it's hooked up to the stock wiring I still get no power. And I did hard wire it correctly with a relay and everything. LightningGSX asked if I had the CEL on? what's the CEL?

LightningGSX · 12-09-2004

CEL- Check Engine Light
There is a input on the ECU that checks for FP power coming out of the FP relay during cranking and run.If the CEL is not on, that should mean you have FP power coming out of the relay, and your problem is probably the wiring after the relay.
Are you sure the injectors stayed open? Thats not very likely.Anyway FP diagnosis is extremely simple, since the circuit itself is simple.Grab a multimeter and start probing points on the above diagram, you should be able to locate the problem in no time.

12-09-2004

Fuel should not be getting past the injectors regardless of if the pump is running constantly. The ecu has control of them and if they are open even if the CAS is not turning then the ecu is fried. Try turning the ignition to run and then turning the cas by hand with your ears near the injectors and/or your fingers on them. You should be able to hear/feel the injectors opening and closing as the CAS is rotated. If the injectors dont click then its liikely the CAS.

CEL = check engine light

caustad · 12-09-2004

I have 2 ECU's one of them I know is good and they both do the exact same thing. I was told that DSM's use grounding signal to tell the injectors when to turn on (Anybody else heard of that?) by a couple of people and thought I probably had a wire pinched or grounded out somewhere. I should be able to find out the problem with a tester and the info from everyone.

caustad · 12-10-2004

Ok so I checked to see if there was power at the fuel pump check terminal while cranking over the motor and there was not. Also, the CEL was not on while turning over the motor. I put my hand on the MPI relay and it clicks when I turn the key on too. Is there any reason to check the CAS at this point? or should I just look for a wiring problem after the relay?