Our Community is 940,000 Strong. Join Us.


Does a GM oil pressure switch serve as a fuel cutoff ?


Pages : 1 [2]

jfishtaker
06-18-2012, 09:01 PM
j cat

Made the splice today, fuel pump runs continuously, motor starts up, runs about 2 seconds cuts off. Will crank right back up, but cuts off.
The 20 second delay is not for this engine model, when I got the component untaped to wire harness it was a omron relay 10052973. No Idea what this controls. Nice to have a wire diagram.

MT-2500
06-19-2012, 08:03 AM
j cat

Made the splice today, fuel pump runs continuously, motor starts up, runs about 2 seconds cuts off. Will crank right back up, but cuts off.
The 20 second delay is not for this engine model, when I got the component untaped to wire harness it was a omron relay 10052973. No Idea what this controls. Nice to have a wire diagram.

Engine run 2 seconds and then shut down is the anti theft system shutting off.

j cAT
06-19-2012, 08:05 AM
j cat

Made the splice today, fuel pump runs continuously, motor starts up, runs about 2 seconds cuts off. Will crank right back up, but cuts off.
The 20 second delay is not for this engine model, when I got the component untaped to wire harness it was a omron relay 10052973. No Idea what this controls. Nice to have a wire diagram.

the ECM is next.

ronlindsey1
08-15-2013, 09:59 PM
Hi to all. Although I just signed on to this forum I have been doing DIY repairs for nearly fifty years. Owned a dozen cars and trucks and always purchased a repair manual to guide me. Seen a lot of funny problems right from the factory one that stumped me the longest was a vacuum hose that was solid rubber for about 3 inches right in the middle. I have replaced a half dozen fuel pumps from mechanical to all electrical units in the fuel tank. I found that to shut off the fuel pp in an accident there is a "crash switch" under the carpet on the passenger side that isn't tied in to the ECM in any way. Also I don't trust manufacture gauges so I always hook up a mechanical oil pressure gauge. As far as the oil pressure switch goes all the older models that had them were only wired to an idiot light. My newest vehicles ( 2004 Buick and 2010 Jeep ) don't even have a oil pressure switch or even an oil pressure gauge ?! Hope this might help.

ronlindsey1
08-17-2013, 12:20 AM
Hi to all again. Mea culpa, mea culpa, maxima mea culpa. Even at my advanced age the taste of eating crow is quite bitter. I rechecked the wiring diagram for the ECM for my 2004 Buick and there for all to see was the fuel pump with two sources of power--one from the control of the power relay and one from the oil pressure switch, a pink wire that was tan in earlier models. Kudos.

MT-2500
08-17-2013, 11:52 AM
Hi to all again. Mea culpa, mea culpa, maxima mea culpa. Even at my advanced age the taste of eating crow is quite bitter. I rechecked the wiring diagram for the ECM for my 2004 Buick and there for all to see was the fuel pump with two sources of power--one from the control of the power relay and one from the oil pressure switch, a pink wire that was tan in earlier models. Kudos.

Ford is the only one that has a fuel cut off switch in case of a crash.
The oil pressure switch used on some older GM trucks was never a fuel cut off switch but a safety switch to keep the fuel pump running incase the relay failed.
But in the early 80's Gm did have a 3 wire oil pressure switch that would shut off fuel pump when it had no pressure after start up.

What model and engine Buick are you referring to that you think has a oil pressure shut off?

Tech II
08-17-2013, 09:07 PM
Agree with MT......

ronlindsey1
08-18-2013, 06:27 PM
This is primarily for MT2500. I just did a google search for fuel pump control operation and think you should read the info from EBAY about this. Search ebay for this.

ronlindsey1
08-18-2013, 09:27 PM
Hey there MT-2500. After checking the wiring diagram for my 2004 Buick Lesabre in my Haynes manual I decided to read the section on Fuel systems. My oil pressure sending unit has 3 terminals ( I think it contains the oil pressure switch). In the notes section it says "If oil pressure drops below the specified pressure level, the oil pressure switch will act as a fuel fuel pressure cut-off device. " pretty interesting and more than meets the eye. Thanks.

Tech II
08-18-2013, 09:51 PM
In the notes section it says "If oil pressure drops below the specified pressure level, the oil pressure switch will act as a fuel fuel pressure cut-off device. "

I believe that is wrong.....the oil pressure switch is in parallel with the fuel pump relay.......so if the relay/circuit does not function on start up, when oil pressure builds up, the oil pressure switch closes to energize the fuel pump....this is a classic example of an extended crank caused by a bad fuel pump relay....

If oil pressure drops too low, the oil pressure switch opens, but since it is an open parallel circuit, the relay circuit is still energized by the PCM, the car continues to run.....

MT-2500
08-19-2013, 09:29 AM
Hey there MT-2500. After checking the wiring diagram for my 2004 Buick Lesabre in my Haynes manual I decided to read the section on Fuel systems. My oil pressure sending unit has 3 terminals ( I think it contains the oil pressure switch). In the notes section it says "If oil pressure drops below the specified pressure level, the oil pressure switch will act as a fuel fuel pressure cut-off device. " pretty interesting and more than meets the eye. Thanks.

I hate to tell you but Your Haynes manual is full of crap.
Every Haynes manuals I have saw will lie to you.
They are a One book fit all like trying to putting socks on a Banty Roaster.:sarcasmsign:

On a 04 Buick LeSabre the oil pressure 3 wires
One is black ground and gray is a 5 volt reference signal and the Tan/white is the oil pressure signal to PCM.
Not even close to a oil pressure safety or cut off switch.

brcidd
08-19-2013, 08:51 PM
Agree with MT the "switch" you reference is actually a 3 wire pressure transducer that monitors oil pressure - same logic is used in a/c high pressure line- to tell PCM when to turn on fans and turn off compressor....

gmc Jay
03-04-2014, 09:48 AM
i have a 1990 Gmc k1500 and it was running and just cut off replaced fuel pump FP relay,computer checked all grounds and nothing in my case could the oil pressure switch be the reason? im stumped

brcidd
03-04-2014, 10:21 AM
Try whaaaaaping the fuel tank while someone else is trying to start it-- FP may be old and armature worn off center- whaaaaaping it can jarr it loose and it can start pumping--if so it needs replaced.

MT-2500
03-04-2014, 10:22 AM
i have a 1990 Gmc k1500 and it was running and just cut off replaced fuel pump FP relay,computer checked all grounds and nothing in my case could the oil pressure switch be the reason? im stumped

No way.
Oil pressure switch is not a fuel cut off switch.
It is a switch to keep engine running in case the fuel pump relay quits.

Does the relay click on and send 12 volts to fuel pump key on 2 second prime up or while cranking engine?

Best to start a new thread on your problem.
Give all info and someone will help you

gmc Jay
03-04-2014, 10:25 AM
No way.
Oil pressure switch is not a fuel cut off switch.
It is a switch to keep engine running in case the fuel pump relay quits.

Does the relay click on and send 12 volts to fuel pump key on 2 second prime up or while cranking engine?

Best to start a new thread on your problem.
Give all info and someone will help you
ok thanks

gmc Jay
03-04-2014, 10:27 AM
ok thanks
i took a power probe and put 12 volts to the Fp and the relay clicks but cant get power to the pump by the key switch

gmc Jay
03-04-2014, 10:39 AM
Try whaaaaaping the fuel tank while someone else is trying to start it-- FP may be old and armature worn off center- whaaaaaping it can jarr it loose and it can start pumping--if so it needs replaced.
i put 2 new fuel pumps in it and replaced Fp relay

MT-2500
03-04-2014, 03:07 PM
i took a power probe and put 12 volts to the Fp and the relay clicks but cant get power to the pump by the key switch

Instead of throwing parts at it and jumping stuff do some proper testing.
Also check fuel pump fuse right hand cowl under plastic fuel pump relay cover.

Get a test light on wire to fuel pump and check for 12 volts with key on 2 second prime up.
The first 2 seconds after key is turned on.
Or on engine cranking.
If you have 12 volts to fuel pump and pump does not run you have a bad pump.
Let us know what you find.

Tech II
03-04-2014, 07:53 PM
I agree....you need to have 12 volts to the pump, PLUS, you need a good GROUND....

j cAT
03-05-2014, 06:58 AM
i put 2 new fuel pumps in it and replaced Fp relay

just remember you need 12 volts and also a ground to get the pump to run. make sure the fuel pump is grounded.

with 12 volts at the fuel pump relay power contacts and none at the fuel pump you have a wiring problem.

Phredster
07-22-2014, 09:59 PM
Ok I have 1994 gmc jimmy 4.3 vortec,.ran off road n down hill, truck wouldnt start sfter cuz fuel pump wouldnt engage, I traced connection and read YES oprs WILLNOT allow power to pump if in accident, I jumped the pins and voila pump sparked to life, I bought n installed new switch and pump now runs, now problem is spider Injectors not sending fuel and yes ive got 60 pounds at schrader valve. Vehicle will only run for short time on ether.

JPs_1996_chevy
02-18-2015, 09:55 AM
Hey, I was reading this post and I was wondering if I could get some answers to a few questions. I had an accident last week and I broadsided a snow bank and my truck will no longer run. there is no physical damage to the truck other then it wont start. I have read several things about it being a fuel pump cutoff switch, an oil pressure cutoff switch, and several other things. I have checked the truck out and I found no cut wires or anything and I replaced the fuel pup within the last month. I don't have a filler neck on the truck currently because someone cut it off and swiped some fuel and I haven't replaced it yet. I did have a small amount of snow enter the fuel tank due to it so maybe the water and snow fried the fuel pump? im not sure. I have talked to shops and other forums and I cant seem to get a clear answer out of anyone as far as what it could be out of the few answers I did get.

maxwedge
02-18-2015, 10:26 AM
Chestertown here, more info needed, got spark, will fire if you spray a small amt of starting fluid into the intake, also you hear the pump prime when the key is first turned on?

Tech II
02-18-2015, 10:59 AM
They cut the top of the fill pipe off? Have a locking cap?

And you have been driving it like this? The CE light had to be on, because of this.....letting snow/moisture in, is not a good thing.....

Do as Max suggested....

j cAT
02-18-2015, 03:20 PM
Hey, I was reading this post and I was wondering if I could get some answers to a few questions. I had an accident last week and I broadsided a snow bank and my truck will no longer run. there is no physical damage to the truck other then it wont start. I have read several things about it being a fuel pump cutoff switch, an oil pressure cutoff switch, and several other things. I have checked the truck out and I found no cut wires or anything and I replaced the fuel pup within the last month. I don't have a filler neck on the truck currently because someone cut it off and swiped some fuel and I haven't replaced it yet. I did have a small amount of snow enter the fuel tank due to it so maybe the water and snow fried the fuel pump? im not sure. I have talked to shops and other forums and I cant seem to get a clear answer out of anyone as far as what it could be out of the few answers I did get.

with the fuel filler cut off water will enter and then settle to bottom of tank. then the sock will freeze then no fuel.

no clear answer because you need to see if at the fuel pump connector you have power also check that ground at the fuel pump frame rail.

being below 20deg f frozen would be a good guess.

Add your comment to this topic!