usmc949803

I have a 92 rs with a 77 350, holly carb. Fuel pump is not work. if i take a wire from battery to grey wire "pin" in relay it works. The electric fan that is hooked up to come on when the key is turned is not working. If i take a wire from battery and put it to the black w/ red wire pin it works. any suggestions. was thinking ecm. and if so how to test ecm

camaronewbie

Your ECM has no control over your fuel pump running or your fan running. Besides, if it's carbed now, your ECM is doing NOTHING!

Fuel pump - ECM only controls the initial priming of the pump, which fuel injection needs - carbs don't need primed since they hold fuel in their float bowls. After the prime, the OPSU runs the pump - it has a fuse in the fender behind the battery in a weatherpack.

Fan - fan works with the fan switch in the pass side head, which you probably don't have anymore, and with A/C.

^^^ That is stock - now for YOUR car....

You should have had an Oil Pressure Sending Unit (OPSU) that was just above the oil filter originally. Has a 3 wire connector to it. If it's not plugged it, or if that OPSU is not on the new motor, then your fuel pump won't run. Here's what I did:

I used the stock fuel pump relay, took the red and orange wires from the OPSU, and ran them up to the stock fp relay. I rewired the relay so it has 1) ground, 2) hot-in-run wire, 3) orange OPSU wire, and 4) red OPSU wire. I turn on car, relay gets energized from the hot-in-run, relay connects the red and orange OPSU wires together when it's energized, and pump runs.

Fan - I used an aftermarket fan controller - they are great! I used a Flex-a-lite, about $90, probes the radiator instead of the stupid fan switch in the pass side head that never works, is fully adjustable temp wise, works with A/C and dual fans, and can be wired to manual on/off switch in cabin. When it senses the temp you set it for, it runs fan at 65% speed (saves battery/alt), and if temps don't reduce in 2 minutes then it kicks in at 100%. It's been in my car 4+ years and always keeps me cool, never failed - best $100 I ever spent! Was very very easy to wire, took maybe 30 minutes.

usmc949803

the fuel pump and fan were both working fine as well as everything else up until two days ago since december. the guy had good intentions with everything but no follow through. been finishing and completing his work

usmc949803

didnt mention also fuel pump is not priming or pumping unless i run wire between batterry and plug for relay into gray wire. also there is voltage at the orangle wire in the relay plug but if i jump it from the orange to the gray nothing.
now for the fan i get voltage into the relay plug but if i jump that into the black w red wire nothing. and if it has to do with oil pressure sensor why when i turn key to the on ( not run) position i dont get pump or fan

camaronewbie

Sounds like the issues are the relays then. I'd trace out the relay wires and see why they aren't energizing. Each should have a ground, a hot-in-run to energize it, a constant 12v+ to supply the power to the fp or fan, and the wire running to the fp or fan.

Zepher

iTrader: (1)

Actually, the OPSU is only there for a backup of the Relay.
ECM keeps the Relay energized when the engine fires up and runs.

NINÅ

usmc949803

the fuel pump is in the tank. actually right now i have it out. made sure it works.

alright heres the breakdown of the plugs at the relays

fuel pump
red - nothing
orange - 12v with key off
gray - goes to pump
black w/white - ground (continuity test)
green w/white - nothing (ground or volts)

fan
red - 12v with key off
brown - 12v with key on
black w/red - goes to fan
green w/white - ground (continuity test)

usmc949803

it is still using the original electric fuel pump in tank

NINÅ

usmc949803

nope havent done that yet. no check engine light. already planned on changing out ecm this week.

camaronewbie

If your not using the ECM for anything but to run the fuel pump, why bother getting another one? Since you've went carbed, and don't have a 700R4 tranny, the ECM is doing nothing at all except priming the pump (which a carb motor doesn't need).

Just connect a hot-in-run wire to the green/white wire on the fuel pump relay and be done - cost = nothing.

But - know that one of these days, the OPSU or the relay will go out and you'll be back to no fuel again. That's what happened to me. That's when I just did it the right way, which was to use the OPSU wiring and run it through the rewired fuel pump relay so I only ever have to worry about the relay in the future and I've taken the OPSU out of the fuel pump equation.

As far as the fan is concerned, the PO obviously has it "rigged" and something that rigged connection has failed - that you may have to trace out yourself and find a solution. Like I said, a seperate fan controller would be the easiest solution, as they don't require any of the OEM wiring to be used except the wire to the fan connector itself.

Zepher

iTrader: (1)

In order for the Pump to stop working (other than pump failure), The relay or ecm, AND the opsu have to fail at the same time.

usmc949803

so just cut the wires that are going to that plug and rewire? also wouldnt that just keep the pump running when the key is on?

Zepher

iTrader: (1)

opsu is wired in parallel with the fuel pump power wire and is normally open and closes with 3+ psi of oil pressure.
If you cut the wires from the opsu and tie them together, the pump will run all the time.

best to keep using a relay and the opsu.

camaronewbie

I had originally wired my pump by running a hot-in-run the the relay to replace the signal lost when ECM was removed. But a year later something went wrong somewhere, and the relay would not run the pump, but the OPSU would. New relay didn't change this, so it wasn't the relay. That's when I jumped the OPSU wires together to get home (I was at GM Nationals in PA and needed to get back to NC). I later rewired the OPSU wires through the relay and everything's been fine since 2+ years now. Don't know what the issue was, the relay was fine, the new relay was fine. I just elimiated the 'ghost in the machine' and now I know how it's wired, instead of guess where the relay wires run vs. the OPSU wires and guessing what operates the fuel pump when.

Like I said, I took the OPSU out of the equation so I'd never have to worry about it again. Another reason - the OPSU can go bad in such a way as to make the pump run 24/7 regardless of the key since it has a direct connection to the battery.

To get going, you can simply run a hot-in-run wire and connect it to the green/white wire on the relay - this will make the relay energize when the key is turned on, thus pump will run when key is turned on.

Later, if you choose to, you can rewire in any number of ways to make your pump work - I just did mine the way I did to take the OPSU out of the equation, and retain use of a relay so that the pump never ran without key on.

And yes, pump will run with key on - that's what you want. No need to have key on unless your driving, no need to have pump on unless your driving.

usmc949803

camaronewbie shoot me an email

usmc949803

fuel pump

tried cutting green/white wire and hooking up to 12v key on. still not working.

usmc949803

shouldnt i just be able to cut the gray wire at the opsu run it up to where the fuel pump relay socket is. cut the gray wire off the socket. tie them together and thats it???

NINÅ

usmc949803

opsu wiring harnass

orange wire - hot
tan wire - key on hot
gray

and the gray at the socket of the fuel relay

camaronewbie

Maybe the relay itself is bad, since you were able to get the pump to run by putting 12v to the grey wire earlier and it worked. I don't know - it's a very confusing system from factory, and the diagram does not help - I've been looking at it for years and still don't understand it compared to what I've actually seen on my car and others. Here's the confusion between the diag and reality:

1) Wiring diag shows the OPSU having orange & grey wire to it, but it actually has 3 wires - there's a red wire as well.

2) The grey wire at the OPSU in the diagram shows as being the same grey wire that runs to the relay, but that is wrong - one of the 3 wires HAS to go to the oil guage itself otherwise it wouldn't work. I don't remember there being any grey wire at the OPSU, there was red, orange, and black - black to guage, red to pump, orange to fuse at battery which changes to red that runs to the power dist block.

So, in my book, the diagram is useless.

There's no telling how/when/why the green/white wire and the grey wire get power - they are both controlled by the ECM. In my book, I went to carb to get away from ECM control - I don't want that stupid box controlling anything! That's why I yanked it out and set fire to it!

But, I do know for fact ... if you tie the orange and red wires at the OPSU together, the pump will run - FOREVER (until battery dies). This is why I chose them - they were easy. I cut ALL the wires off the fuel pump relay, leaving 4 inches of wire on the relay connector. Then I wired as such:

hot-in-run ----> green/white
ground ----> black/white
OPSU orange ----> grey
OPSU red ----> large red

Nothing is connected to the small red on the relay connector - it's taped off.

This runs the fuel pump whenever the key is "on". It's simple, clean, takes the ECM and the OPSU out of the equation. With this, if my fuel pump does not work, there's only 2 possibilities - 1) bad relay, or 2) blown fuse in the fender at the battery. It's run perfectly fine like this for 2+ years now with no issues.

You just have to be careful with how you rig the OPSU wires, since they have a direct connection to the battery regardless of the key, you can end up with the pump running 24/7, killing the battery and putting alot more runtime on the pump. That's why I used the factory relay to turn that connection on/off.

usmc949803

well that sounds like the route im going to go. been three days of constant tracing and checking and NOTHING lol.

at the fuel relay plug i have

red wire
orange wire
gray wire
black/white
green white

OPSU

gray
orange
tan

Supervisor42

If that's the case, either the relay is bad, or the voltage on orange wire is going away, or the black/wht ground wire is not letting the relay close.
Ignore the OPSU, it's useless.
Here's a schematic for an '88 with TBI that may help.
The '92 should be similar. You may want to check the wiring that goes to the battery stud on the fender.
The F/P relay gets its power (orange) from that stud thru that lonely little fuse bouncing around above the steering box.

usmc949803

you are talking about the ground wires that are bolted to fender right near battery and 20 amp fuse that is right above it

Supervisor42

Oops. Wrong model. I was talking about small wire that comes off the positive terminal. The '92 is probably different.

usmc949803

ok heres what ive done today

i check the orange wire at opsu and fp connecter. every time i put a jumper between gray and orange wires (fp and opsu) connecters i lose voltage. i cut both oarange wires at both connecters. i took a wire ran it from battery (hot) split it and attached to orange wires on connecters. i jumped the gray and orange wires again through the connecters and pump runs. but constant.

Supervisor42

Put a fuse in your "new" orange wire, the fuel pump is inside the fuel tank and that's a bad place to have an unfused short circuit.
Once you have a new fused source for your orange wire, renew your switched ignition source to your green/white wire at the F/P relay and you're done.

usmc949803

the green/white wire out of relay looks like it still intact going to ecm. out of daylight. will continue hunt tomorrow

NINÅ

cfreebird305

Thank you guys very much for this post, I have an 88 t/a with a 5.0 tpi I just installed, I couldn't get the pump working for the life of me but after seeing how you guys wired it I got my car fired right up! thanks again!