The problem started with some hot start issues and has gotter worse. It ran great, it just wouldnt start unless it was cold. I have a known good fuel pump with some electrical issues related to the pump. I know the pump is good because when I splice 12V power to the grey wire in the fuel pump wiring harness downstream of the connector under the vehicle (right behind the drivers seat), it will start and run fine. I have actually driven it that way with no problems. Once it is running, it stays running, even if I disconnect the "hot" 12v feed. I replaced the relay, and I hear it click when the key is turned. When I probe the green wire with the white stripe in the underhood fuse box, I get 12 volts for about 2 seconds when I turn the key on, or continously when the van is running (I don't know if that wire is the one to the relay of from it). What really confuses me is that I also get 12v on the pin in the connector under the car where the gray wire to the fuel pump connects, but it still wont start unless I run a "hot" wire. I know GM did something with their oil pressure switch, but wouldn't I not get power to the connector if that was the problem? Any help is appreciated. Thanks, Justin
You are right about the grey wire and the oil switch. Gm had big problems with the square connectors at the pump module with the ground side not connecting well. If you replaced the module, then you should have replaced the connector provided.
What was the actual pressure? It can still run on low pressure but not start on low pressure hot.
October, 2, 2012 AT 4:59 PM
Sorry for the late reply. Your reply was filtered to my junkmail box and I just found it. I don't have a fuel pressure gauge, but when I tried to rig up a generic vacuum/pressure gauge, it blew the hose off, so there is decent pressure. The pump itself is new, although I did not replace the whole module. I did replace the oil pressure gauge since my initial question, and there has been no change in symptoms. I don't think it's a fuel pressure issue, since it will start right up if I use a jumper to run 12v directly from the battery to the gray wire, and will continue to run when I remove the "hot" 12v lead. I suspect a sensor issue somewhere that is effecting the computer somehow, but I'm not sure how to diagnose that. I thought it might be a wire or connector problem, so I tried to run a new wire from the fuse box to the pump by splicing into the dark green/white wire in the fuse box directly to the gray wire before the pump. No change. The green/white wire has power at key on for about 2 seconds, so I'm confident both the new and old solenoids are working correctly. I do wonder though, is that wire the wire from the computer to the solenoid, or from the solenoid to the pump? If it is computer to solenoid, which wire would run from the solenoid to the connectore where it becomes the gray wire. There is no gray wire coming out of the bottom of the fuse block in the solenoid location that is gray, although there is a larger gray wire coming from another location on the fuse block.
October, 3, 2012 AT 12:13 AM
Is there a connector at the bottom of the car by the rear door where the grey wire comes out of?
October, 3, 2012 AT 4:00 AM
Yes. That is where I currently have the hot 12v wire from the battery connected. Before I only needed to connect that 12v wire to start the car, then I could disconnect the 12v jumper and it would continue to run. As of today, when I disconnect the 12v jumper, the pump will shut off and the car will stall. The problem is, I dont want to have to pop the hood every time I drive and every time I shut the car off. If I leave it connected, the pump will continue to run, even when the car is off.
October, 3, 2012 AT 11:08 AM
Just as a thought, go to the oil sender switch by the oil filter and check the grey wire and see if it is frayed, bare or hitting anything.
October, 4, 2012 AT 3:20 AM
I have not had a chance to check the wire at the oil pressure gauge, but when I replaced it, the wire looked fine. I'll check it again. When I got home today, I shut off the motor and then opened the hood to disconnect the "hot" wire to the fuel pump and I noticed I could not hear the fuel running thru the system like I normally can when I have 12v connected, even with the key off. What are the possible consequences of having the wire run this way? Is it possible the computer controls flow by supplying less than 12 volts to the pump, and that by having 12v constantly to the pump that it is causing some kind of damage? The pump is new, even though the module is not, and probably has less than 100 miles on it. 1 new development is that it does not always stay running if I disconnect the hot 12v power like is was doing before. Disconnecting that power wire can cause the motor to starve for fuel and stall. When I drove it to work this morning, it started right up without the constant 12v wire connected, and ran fine for the 1/2 hour commute to work, but when I tried to start the car 11 hours later to go home, I had to connect the jumper to get it to start.