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Fuel pump oil pressure switch relationship

Tiny
JON HOPCIA
  • MEMBER
  • 1995 OLDSMOBILE CUTLASS
  • 3.1L
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 125,000 MILES
Hello and thanks in advance. Much misinformation on the internet. Hard starting. Every time I disconnect/reconnect oil pressure sender harness I can here fuel pump engage while ignition starting. Car dies while driving. Turn ignition and can not hear fuel pump go on. Disconnect/reconnect oil pressure sender harness. Hear pump engage when ignition on and starts. Car dies while driving especially steep hills reverse or forward. Finally disconnected oil sensor harness from sensor and now no problems except harness is disconnected from oil pressure sensor. Can you figure this one out please?
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Monday, March 20th, 2017 AT 8:15 PM

11 Replies

Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
It may be a short in system but try a new switch first that may be the problem otherwise it's shorting out someplace.
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Tuesday, March 21st, 2017 AT 6:33 AM
Tiny
JON HOPCIA
  • MEMBER
  • 6 POSTS
Hello! I thought with the information given, I could avoid trying to replace this and then do that and then replace this. I was looking for a more definite answer on how the oil pressure switch and fuel pump are related to each other. Also, I have a warning light on my instrument panel that says "low oil level" in addition to the oil can light. Is that two different sensors?
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Thursday, March 23rd, 2017 AT 11:25 AM
Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
Yes they are the low oil level is exactly what it means the sensor is in oil pan a lot of times the fuel pump relay is to run the pump on startup and then if required during running of engine. The oil pressure switch sends a signal to the pump/relay as well as the dash if pressure gets low pump quits. But since you disconnected it it can't do that as well as give any oil pressure readings. If the low oil level light is on and you haven't checked the oil then it may be so or it's a bad sensor/shorted wire. See pic
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Thursday, March 23rd, 2017 AT 12:06 PM
Tiny
JON HOPCIA
  • MEMBER
  • 6 POSTS
But with my oil pump pressure sensor disconnected, shouldn't my oil pressure be sent as 0 and shut off fuel pump?
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Friday, March 24th, 2017 AT 1:59 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 47,513 POSTS
Hi Jon,

If I may jump in here, yes the oil pressure sender does interrupt the fuel pump to stall the engine. Here is a wiring diagram so you can see exactly how the system works.

Please let me know if you need anything else to get the problem fixed.

Best, Ken
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Monday, March 27th, 2017 AT 7:58 PM
Tiny
JON HOPCIA
  • MEMBER
  • 6 POSTS
Thank you Ken! I think this will get me to a solution.
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Tuesday, March 28th, 2017 AT 3:30 AM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 47,513 POSTS
Good to hear, please use 2CarPros anytime we are here to help.

Best, Ken
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Tuesday, March 28th, 2017 AT 6:19 PM
Tiny
JON HOPCIA
  • MEMBER
  • 6 POSTS
FIXED! Thanks to the wiring diagram. My intention was to hotwire my fuel pump to see if it worked. I followed fuel pump wire from fuel pump relay over to the left(drivers) side and along the route on the left side of the engine I found a loose ground that connected about 4 or 5 wires to the engine block. No wonder why I had intermittent problems through the last year or so. So HMAC300, you were on to some thing from the start and Ken helped me clinch it with the wiring diagram. No parts replaced and works fine now for days. ONE QUESTION THOUGH, the wiring diagram only shows two wires coming from the oil pressure/sensor switch and there are actually three. Can you please clarify? Thanks so much for the help, aloha, jon
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Tuesday, April 11th, 2017 AT 10:30 AM
Tiny
JON HOPCIA
  • MEMBER
  • 6 POSTS
And why is there a solid line around the fuel pump relay and dotted lines around the oil pressure sensor/switch in the wiring diagram? Where is that diagram from? Thanks again, jon
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Tuesday, April 11th, 2017 AT 10:35 AM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 47,513 POSTS
Glad you could get it fixed please use 2CarPros. Com anytime we are here to help

Best, Ken
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Tuesday, April 11th, 2017 AT 2:06 PM
Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
The other line is more than likely a ground for the light/gauge in dash. The dotted lines mean that where they come from that something else uses the same ground at the dot and dotted line shows where the ground wire connects to
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Tuesday, April 11th, 2017 AT 3:14 PM

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