Eddie77

Will a bad oil pressure switch or a bad oil pressure sending unit shut down my fuel pump.....and if i replace them will it fix my low oil pressure problems...

Joe K

I believe that it will cause a no start. Did you make sure you didn't disconnect or knock loose something? Saw the other thread about your oil being changed.

playsdixie

I think you have asked and answered your own question....a fuel pressure gauge on the rail will tell you.....

Kevova

You need to install mechanical fuel pressure gauge in place of the 1 wire oil pressure sender and see what oil pressure is. Fuel pump oil pressure switch (2-3 wires) will turn on fuel pump at around 5 psi. At 5 psi or less i would expect engine to atleast be clattering if not knocking when revving.

gpierce

NO. It is a backup to the ECM.

gpierce

Oil pressure switch malfunction causes fuel pump inop = Super DUPER common myth.

Here's how the fuel pump system actually works:

When the ignition is first turned on the FMD (Fuel Management Device) integrated circuit inside the ECM (Electronic Control Module -- the "computer") turns on the fuel pump via the fuel pump relay for 2 seconds. The purpose of this is to prime the fuel rails in preparation for starting the engine. The ECM shuts off the fuel pump after 2 seconds so that it will not run continuously if the ignition is turned on but the engine is not started. When the ignition switch is turned to the crank position the engine starts rotating and the ignition module inside the distributor starts sending out DRPs (Distributor Reference Pulses). When the FMD IC detects DRPs it turns on the fuel pump relay. The FMD will keep the fuel pump relay turned on as long as it receives DRPs, which means whenever the engine is rotating, whether cranking or running.When the oil pressure reaches about 4 PSI the oil pressure switch (which is in parallel with the fuel pump relay) will also turn on. This is a backup for the fuel pump relay in case the fuel pump relay fails.

Eddie77

Fuel Pump Shut-Off Switch (Low Oil Pressure)A recommended safety feature when using an electric fuel pump, this switch automatically cuts power to the pump when oil pressure is lost to help reduce the fire hazard in case of an accident

gpierce

84-89 C4 doea not have this. I dont know about later C4s.

Eddie77

What is the difference between a oil pressure switch.....and a oil pressure sensor..

gpierce

The switch switches a circuit open or closed, the sensor sends a signal that something else interprets as a pressure reading, usually a resistance value.

Eddie77

If I'm having low oil pressure problems which one would I replace the sensor or the switch

gpierce

Not sure what you mean by "problems". The reading on the dash is from the pressure sender/sensor. If the sensor is faulty you will have inaccurate readings.

Eddie77

Im not talking about what the gauge on my dash is reading or not....my question is if a motor has low oil pressure is there a sensor or switch that can be replaced on the motor to fix a low oil pressure problem..

gpierce

If you actually have low pressure, then there are no electronics that are going to fix that Do you know how oil pressure is produced in a car's engine? Should probably look that up

Eddie77

I can't get the car started to find out if the oil pressure is low or not I've had trouble with his car stalling out and I heard if a car has low oil pressure for it'll shut off the fuel pump....
I've done changed the mass airflow sensor with a mass air flow sensor relay the ICM unit mass air flow sensor burn off unit put a new fuel pump in it change the fuel filter the car will run for a few minutes then it appears that the fuel pump shutting off

Eddie77

I never had this problem till I my car up to get the oil changed and put the ICM unit on it and then they said my car wouldnt start but a few seconds and they wanted $91 an hour to try to figure out what was wrong with it so I had it towed home

cdm747

I am attaching a PDF of the fuel circuit for an 88, this is out of the 88 Electrical FSM. There is most definitely an oil pressure switch in the circuit for the fuel pump.

gpierce

I answered this earlier in the thread. A faulty oil pressure switch will NOT cause your fuel pump to turn off.

To confirm, your problems started after you had your oil changed and a new Ignition Control Module put on? Why did you put a new ICM on it? What brand ICM did they use?

I think realistically you need to start at the basics. Do you have fuel pressure when you turn the key to run and does it remain steady? If not you could have a bad fuel pump relay, bad wiring to it, or faulty ECM.

cdm747

gpierce I totally disagree with you. Look at the circuit. On the power to the fuel pump relay from the ECM it states Fuel Pump Control during start only. The circuit to the fuel pump is fed through the Oil Pressure Switch during normal operation. Please look at the wiring diagram I uploaded.

Tom400CFI

I think ^you^ need to look at the diagram. (you didn't post one, BTW)

gpierce is absolutely right. The oil pressure swtich is a back up redundancy to, the fuel pump relay. IDK WHERE in the world you came up with verbage that says the ECM only commands the pump to run during cold start only. Leesvet?