Olds fuel pump won't shut off.

applejoe

93 olds hanged ecm 2supeme s w/3.1 liter v6. fuel pump keeps running after key (ignition) turned off. check ignition switch, ok, remove relay still runs. checked wires in trunk coming from gas tank ok. changed ecm 2x car thought 1st was defective , will crank but not turn over. put back old ecm car cranks and starts right up. to shut fuel pump have to disconnect wire to battery. any help appreciated applejoe

imidazol97

applejoe said:

93 olds hanged ecm 2supeme s w/3.1 liter v6. fuel pump keeps running after key (ignition) turned off. check ignition switch, ok, remove relay still runs. checked wires in trunk coming from gas tank ok. changed ecm 2x car thought 1st was defective , will crank but not turn over. put back old ecm car cranks and starts right up. to shut fuel pump have to disconnect wire to battery. any help appreciated applejoe

I can't get a diagram for your particular car but I checked another GM circuit from 1993
for the Buicks. It shows a second path for power to the fuel pump which is through the oil
pressure switch and that fits with my memory and first thought when I read your problem.
The oil pressure switch is providing power. I assume it's faulty. I was thinking the
relay just provides a prime when the key is turn to ON and the power is run
through the oil pressure switch so that if the engine goes off, the fuel pump goes
off.

There should be a fuse for the oil pressure switch powering the oil pressure
sender and the fuel pump power. IN the car I'm looking at it's a 20 amp fuse
in the relay center.

Does your oil pressure have a gauge or just a light that's supposed to come on if
pressure goes too low? If it's a light, does that light come on when you turn the key
to on before starting? If it stays off, indicating that the engine has oil pressure,
that may be proof your pump is being powered that way.

applejoe

thanks for your help. had 3 mechanics look at the problem they couldnt figure it out 2 suggested a on ff switch be installed are they for real. your answer makes sense.. will try changing switch 1st chance applejoe

thecardoc3

The oil pressure switch was a second way of powering the fuel pump in case the relay failed. The relay was intended to be the primary driver for the fuel pump circuit and the oil pressure switch was just a back-up system that would take over operation of the fuel pump based on the engine oil pressure if necessary.

You also commented about talking to three "mechanics" and if they were for real. There are so many different ways to answer that. They can call themselves mechanics if they want to and almost nobody cares if they were nothing but DIY'ers the week before and have no real training and experience at all, until they fall short of someone's expectations that is. An experienced technician would have had no problem solving this even if he/she didn't know the silver bullet answer (the oil sender) the very first time they encountered this symptom. For that matter its the inverse of a problem that used to occur on carbureted Buick engines back in the mid 80's when they first went to electric fuel pumps and did use the relay to only prime the system and then the oil pressure switch kept the pump running, that is until the engine lost oil pressure during an extended idle.

Through the years there has been more consumerist pressure to force repair pricing down below where it legitimately should be and there is a cost to the consumer for that which you just got to see what it really is. The techs who make solving problems like this look easy don't do it for free and they can't no matter how popular it may be to others to try and make it be that way. You'll see constant complaints in just about any forum including this one where owners put any diagnostic fee under fire with comments like "They want a hundred dollars just to hook a machine up to it" and its funny when other consumerists can't separate the wheat from the chaff and blame top techs for that perspective too. So from my POV they are/were not mechanics if they didn't have the knowledge and skill as well as charge correctly to take the time and test the system correctly in order to give you a solution to the problem. However they likely do the easiest stuff much cheaper than what it should really cost so they aren't going to go away any time soon. Meanwhile it will continue to get to be more difficult to find techs who would have solved this so fast it wouldn't even have gotten any attention at all. Well, unless someone want to complain about the price then they would be faulted for being able to deal with it.

applejoe

to imidazo197 and cardoc3 . u were right on , the oil pressure switch or sender was the problem, changed it and car works fine thanks for ure help