raypdq

Conflicting information on the existence of a fuel pump circuit that can be interrupted by a fuel pressure switch that opens when no oil pressure is detected. 1990 base coupe I get 2 second pulse at fuse with meter when key is turned on. With meter and hearing the fuel pump comes on when key is turned on for 2 seconds. I have replaced a fuel pump less than 1 year old with new. I could not here it and thought that I had ruined it by using injector cleaner through the system. I replace it again because after I used the cleaner it went from instant fire to a half a crank, that was the reason I install the other one because of multibal cranks on cold starts. I have also replace the relay, fuse and single wire plugged oil oil pressure switch. There is a second unit installed in the same channel aboout and inch longer that has 3 wires in the plug and I would suspect that it would be the pressure switch for the fuel pump circuit. If anybody know for sure I would appreciate a reply. This unit is extremly difficult to get to so until someone can verify that it is a interupter for the fuel pump I a not going to stand on my head to try to replace. Also it would be nice if someone for sure which wires on the plug to jump to by pass the oil pressure switch. Thanks Raypdq

65Z01

The oil pressure sw has two wires, Orn and Red.

You can force the FP to run by jumpering +12 vdc to ALDL port G.

Have you checked the fuel filter to see if it may be clogged?

aklim

From what I saw, it was a backup that would run the pump as long as there was oil pressure.

Yes, that is the prime charge

If anything would be ruined it would be the injectors from the snake oils you are trying to use to clean stuff. If they are Multecs, they get fuel cooled so the snake oil in the fuel eats at the coils and causes problems. Same with ethanol gas which is why I will change any Multec out.

arbee

This switch is not a fuel pump interrupter but rather an additional fuel pump "on" device.

xrav22

The unit is supposed to kill the engine when the oil pressure is 0. On the other hand if it is bad it may not give the signal when starting. My oil pressure was bad(1 prong) but I changed them both anyways while I rtv the stalk and cleaned up the area.
Good luck
This is 85 I think yours is the same.

raypdq

Thank you for responding
So is this a parrelal circuit, does it run to the fuse or through the relay contacts or is a circuit to activate the relay. Where does the primary run circuit originate from the ecm, I know my 2 second pulse circuit is puling the relay as mentioned before because I have heard and meter tested the pump running. I am confused if the oil pressure sws circuit is a parallel circuit then it if opens because of oil pressure failure what good does it do if it dosen't diable the primary circuit. When I replace the fuel pump last year I also replaced the fuel filter. I don't know if I mentioned it before but I am working without the aid of a wiring schematic. Raypdq

xrav22

From looking at my FSW the orange is HOT at all times and then with pressure the sensure opens and the red is then hot. I would say after a year the pump could have an issue. Good Luck diagnosing.

aklim

I have started my car with the switch disconnect It is a backup

RollaMo-LT4

No, it will not.

playsdixie

you have several threads in tech on the same issue???? do you have a gauge on the schrader valve so you can see fuel pressure ???...all this technical searching you are doing is useless without it...if, you hear the fuel pump turn on for 2 seconds, and have no pressure at the rail...the fuel line is disconnected in the tank....or, your pump is no good...don't know if your year had a "pulsator" after the pump, most new pumps come with a hose to eliminate it....

arbee

Because it was not designed as a fail safe for 0 oil pressure. It was designed as a backup to run the fuel pump if the fuel pump relay failed. The easiest way to see if your relay is working is to run the engine and then unplug the pressure switch. If it stays running, the relay is working.

raypdq

This is a 1990 base coup, from 89 to 90 all this wiring and relays and oil pressure switches or different. I am assuming that that stayed constant through 96 but don't know for sure.
I got a fuel gauge and also jump the pins on the oil switch to get the circut to the pump. pump is always on with the fuse in even when the ignition is off. I have 44 lb on the gauge and when I remove the fuel pump fuse it drops to 41 and holds, after 2 hours with the pump off it is still 36 lb. Crandked would not start maintained 41 lb during the crank. I have 2 fuses for the injectors a 20amp, 8th position and a 10 amp, in the 13th positon in the fuse chart and both checked good. Reading across the fuse contacts with ingniton on I only get a 2 volt reading on both of the fuse contacts. If I use a different ground circuit I get 12 volt on both of the fuse contacts for the injectors circuit. So I have voltage to the fuses but only 2 volt reading when using their ground circuit. Do you know would the coils in the injectors cause the voltageto drop? I pulled a plug and it was dry. Does anyone know the circuit path of the injector circuit, is it controlled by a relay also. Original problem stoped cold will driving like the key was turned off. Any help would be apreciated. Thanks Raypdq

aklim

You will need to get noid lights like from Autozone to test injection pulse. Pressure seems ok

PatternDayTrader

Do you have spark ? Because if the answer is no then don't expect your injectors to pulse.

raypdq

I will have to get help to check the spark, I have been chaseing this problem around with in 95 degree weather and a bad back by myself. Its been a little tough to concentrate and focus actually a little scattered in my trouble shootig. Do you know is the coil part of the distributor cap and located somewhre else. If I do have spark where would be the next logical place to look for injectors failure to fire. It seems like like many electrical things where changed in the 1990 model year and most of my replies have been from members with cars in the 80's there are some constance but even though well intended the help has limeted value. Thanks for your help!
Raypdq

aklim

IIRC, the coil is on top of the distributor. I only saw it for a few minutes before I sold the motor to someone. I run a small coil now since it works better for the Holley Stealth Ram.

If you have spark, the next thing I would do is check for fuel pressure. If it holds pressure for a while you need to "rent" a set of noid lights at Autozone that will test for injector pulse. If you have pressure and pulse then the injectors might be problematic.

raypdq

[QUOTE=aklim;1597420420]IIRC, the coil is on top of the distributor. I only saw it for a few minutes before I sold the motor to someone. I run a small coil now since it works better for the Holley Stealth Ram.

If you have spark, the next thing I would do is check for fuel pressure. If it holds pressure for a while you need to "rent" a set of noid lights at Autozone that will test for injector pulse. If you have pressure and pulse then the injectors might be problematic.[/QUOT

Since the shut down was so definite I hoping to find the silver bulet that would take down the operation so sudden. I think I have pretty much eliminated the fuel system to the injectors I am concentrating on why the injectors are not pulseing. I haven't been able to find a warm body to help me check my spark, so I am kind of out of business for today. I went on line to the Public Library and search Chilton Repair manual and got some pretty good poop on the electrical. fuel and injectors systems soI am not going completely by the seat of my pants. I will look it over tonight and plan my attack for tomorrow. Thank you for your imput and your help. Raypdq
PS I don't if I posted it to you but I do have 44 ll fuel pressure on the gauge and it holds to 41. Still 36 half hour later. I would say that is okay, at least to start.

aklim

Fuel pressure is ok so have you decided they are not pulsing and how did you determine that? If it is definitely not pulsing, we can look elsewhere but if you haven't determined that, you should start there before tearing down anything else.

raypdq

The evedence I have of that was I pulled a plug and it was dry but it was some time after I had cranked it. Because of the Fathers day week end having trouble finding somebody free to crank whil I check for spark. Now baterry dead, charging and will probably give it a rest for today. Thank you for all you attention and input to my problem, enjoy your day.

Raypdq

aklim

If there is pressure in the fuel rail, you need to check if the ECM is pulsing the injectors. Just because there is no fuel in the cylinder does NOT mean that the injector is pulsing