TeeJay3800 Posted August 4, 2005 Report Share Posted August 4, 2005 Its been a long time since I've posted here, so hopefully this is in the correct section. My fuel pump has been staying on after I shut the car off. I replaced the fuel pump relay thinking that would fix the problem, but the pump continues to run even with the new relay. After a while it seems to shut off by itself. What would cause the pump to stay on other than a stuck relay? The pump also sounds different than it used to. It's sound is kind of a lower tone than it used to be. What else should I look at besides the relay?? Thanks guys Quote Link to comment Share on other sites More sharing options...
Stekman Posted August 4, 2005 Report Share Posted August 4, 2005 Sonds like the oil pressure switch is sticking and keeping the pump on. Try replacing the oil pressure switch. Quote Link to comment Share on other sites More sharing options...
TeeJay3800 Posted August 4, 2005 Author Report Share Posted August 4, 2005 Its weird that you mention oil pressure because my oil pressure gauge has been doing some strange things lately. Sometimes it will be normal, other times it will be stuck pegged on max. Where is this switch and how hard/expensive is it to replace? Thanks for the help. Quote Link to comment Share on other sites More sharing options...
Stekman Posted August 4, 2005 Report Share Posted August 4, 2005 I'm new to the W-body and their associated engines myself, so as far as it's specific location, I do not know. I just know that the general oil pressure switch circuitry hasn't changed much from car to car. Try looking down by the oil filter. You will be looking for something that looks like this: It has 3 wires in its pigtail. As far as your gauge reading funny, yea, that makes sense, especially if you have a combined sensor for the gauge and a switch for the fuel pump circuit. As for replacing, when I had to replace my Camaro's, it was only like $20, it's not an expensive part. As for difficulty, it's not too bad (depending on location). just unplug the pigtail and get a wrench around it's base and take it out. Quote Link to comment Share on other sites More sharing options...
TeeJay3800 Posted August 5, 2005 Author Report Share Posted August 5, 2005 I'm not sure about the oil pressure switch, but I know the oil pressure sending unit is right next to the oil filter. I'm assuming on our engines its the same thing. Since my gauge has been acting funny, I'll take that as a sign that the unit is bad. If the fuel pump runs based on oil pressure, and the sending unit indicates high pressure (engine running), that might explain why my pump continues to run. You think replacing the sending unit will fix both problems? Quote Link to comment Share on other sites More sharing options...
Stekman Posted August 5, 2005 Report Share Posted August 5, 2005 Take a close® look at your sending unit and count the wires. If there are 3, it's the combined switch/sender. The oil pressure switch acts as a back up to the fuel pump relay. Should the relay fail during engine operation, the oil pressure switch will continue to supply power to the engine, given there is enough oil pressure to close the switch (which is usually about 4 psi). Before GM got crafty, they installed 2 seperate devices for each the gauge and the fuel pump circuitry. Around the late 80's they combined them into 1 unit. Both run off the basis of detecting oil pressure. Should it become defective, it reads an incorrect pressure meaning after you shut down, the switch, being defective and sensing incorrect or non-existant pressure, will in turn, close the switch keeping the pump powered. If you have a 3 wire sender, I do think it's a kill 2 birds with one stone type of deal. Quote Link to comment Share on other sites More sharing options...
Brian P Posted August 5, 2005 Report Share Posted August 5, 2005 good diag! Quote Link to comment Share on other sites More sharing options...
TeeJay3800 Posted August 5, 2005 Author Report Share Posted August 5, 2005 good diag! I agree, thanks Stekman! I found out that the 3.1 does indeed have a combination switch/sending unit. I'll just replace it and I think I'll be golden. Thanks again. 8) Quote Link to comment Share on other sites More sharing options...
DaveFromColorado Posted August 5, 2005 Report Share Posted August 5, 2005 I thought the purpose of the pressure switch for the fuel was actually so if you lost all your oil pressure it'd kill the fuel pump.. my old beretta did that too, it'd run the pump all the time, I got into the habit of pullin' the fuse for it every time I got outta the car, but when I replaced that sending unit, it fixed the problem. --Dave. Quote Link to comment Share on other sites More sharing options...
Robby1870 Posted August 5, 2005 Report Share Posted August 5, 2005 I thought the purpose of the pressure switch for the fuel was actually so if you lost all your oil pressure it'd kill the fuel pump.. my old beretta did that too, it'd run the pump all the time, I got into the habit of pullin' the fuse for it every time I got outta the car, but when I replaced that sending unit, it fixed the problem. --Dave. See, I talked to TeeJay last nite and I thought the same thing. It didnt make sense that if the oil pressure sender was giving a reading it would force the fuel pump to stay on even though the ignition was off. Oh well, if this fixes his problem, I will have learned something Quote Link to comment Share on other sites More sharing options...
GnatGoSplat Posted August 5, 2005 Report Share Posted August 5, 2005 I thought the purpose of the pressure switch for the fuel was actually so if you lost all your oil pressure it'd kill the fuel pump.. That would have been a logical conclusion, but no... it's wired in parallel. It's a backup, not a protection device. Quote Link to comment Share on other sites More sharing options...
TeeJay3800 Posted August 5, 2005 Author Report Share Posted August 5, 2005 Dave, I've been pulling the fuse once in a while too. Don't you love how your ECM gets reset every time you do that? I'll replace the sending unit/pressure switch/whatever it is and let you all know if it fixed the problem or not. Quote Link to comment Share on other sites More sharing options...
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