Long story short, I believe something's wrong with my 91 RS's fuel pump wiring......because sometimes it primes (after which, the car starts) and sometimes it doesn't. My question is (and yes, i have searched and couldn't find anything for TBI cars...) where are the fuel pump relay and fuel pump fuse, and anything else i would need to check to see if it's a wiring problem vs. a pump problem? I found a checklist posted by TomP, but it's for 2.8 MPFI or V8 TPI. By chance, are the locations the same for our TBI cars? I'd appreciate any help ASAP, as I need this thing running by tuesday.

 

Fuel Pump Relay on my 90 RS is on firewall, driver side, almost against fender. Two relays there on the back side of a bracket that attaches to firewall - 1 relay is cooling fan, the other is fuel pump. Both relays themselves identical - identical part numbers. Hope that helps.

 

There are 2 relays up on the firewall next to the brake booster. I can't tell you if the one furthest away from the engine is the fan or the fuel pump but that's the location. GM made it so that they clip in but to get to one you need to remove the other. So if your relays were ever taken out, checked, or replaced, it's likely that they were switched. Hence the reason I can't tell you which is which. Now to make life easier I believe the fuel pump relay has 5 wires coming out of it, the fan only has 4.
I've attached a document of the wires. The fuel pump relay is off on the left. To check if the pump is priming just turn the key to the on position and listen for the pump to come on for a couple seconds. To hotwire the pump just use a paperclip.

 

yo' jprevost i got some questions for you if you don't mind.
e-mail me please.

 

the cooling fan relay has heavier AWG wires coming out of it

 

Alright guys, I checked the pump relay, and I got a good hot signal coming through the orange wire from the battery. I jumped the hot wire with the fuel pump prime wire and nothing happened. So I went under the car near the tank and "test-lighted" the connector right in front of the gas tank. Sometimes I would get a REALLY weak signal out of the middle port (we're talking under 1 volt here) and sometimes i would get nothing. I can't tell what color wires go into the connector from the front of the car (because the connector is stuck right into the body of the car), but the wires going to the pump are black, purple, and grey. I disconnected this connector, and then plugged it back in. One time I got the thing to actually prime, after which it started right up. I then moved it back into its spot in the driveway, shut it off, waited a minute or two, and then checked to see if it would prime again. Nothing.

I'm thinking there's a faulty connection somewhere, but I'm not sure what's between the relay and the rear connector that could be coming loose. I can't see anything on the wiring diagrams, and I was wondering if anyone can figure this out.

 

You have to wait a good 30 sec between priming. Got this straight from the GM techs when I was trying to figure out what was wrong with my fuel pump.

You may want to check how your fuel pressure holds though.

If your losing pressure immediately after shutting it down then you wouldn't be able to get it to start immediately. A few TPI people I know are going through this issue where they have a hard time starting sometimes because the system loses pressure due to leaky injectors or a valve in the pump is busted.

 

I waited more than 30 seconds before i checked to see if it would prime --- and it didn't.

I'm pretty sure there's a bad connection somewhere that causes it to work sometimes, and then not work most of the time. I just can't figure out where it could be.

 

Did you try switching the relay with the fan relay? They're the same so this could rule out the relay. Next I would get a fuel pressure gauge and the t-fitting, check the fuel pressure and make sure it isn't bleeding off really fast. If it is, you've got either an issue with the fuel pump or the FPR. If you believe it's a bad wire, use a multimeter and check to make sure there aren't any high resistance lines. GM was pretty good with the wires and making sure they don't get broken, especially the fuel pump. It still could be a reason since after the engine has cranked for a while, the oil pressure will activate the fuel pump (bypass safety feature). The reason I don't think this is the case is because on a warm restart (like you tried) the oil pressure switch will turn the pump on almost instantly.
I think this is going to be something obvious.

 

i still just don't know why i'm experiencing such a drop in voltage between the relay and the under-body connector. does anyone know the connector i'm talking about? With a test light, I would sometimes get a REALLY weak signal out of the middle port of this connector (under 1 volt) and sometimes I wouldn't get anything. I would imagine I should be getting 12 volts at this connector, which is why I suspect it's a bad wire somewhere. But I just need someone to confirm what this connector is for and what each port in it is for, as well.

 

Oh yeah....and I switched the relays too, and it still didn't work, so I think I can rule them out. Something else has got to be wrong.

 

Did you check the wires for continuety to the fuel pump relay? It's not hard, just put the multimeter to the speaker, touch the terminals to make sure it goes beep, put one on the harness (fuel pump unhooked) and another on where the wire goes to the relay. If it beeps/buzzs it's good, if not, it's bad. Did you bypass the relay with the paperclip to see if the fuel pump would go on?

 

Yes...I checked the "hot" wire coming to the relay, and I'm getting 12 volts. I then jumped the "hot" and "fuel pump prime" wires, and I got nothing. And like i said, i'm getting a tremendous voltage drop between the relay and the rear connector. I need to know what the three wires on the connector are for, because I don't know what each wire does. In the mean time, I'll check all 3 for continuity.

 

HTH's: it looks like the purple is the tank fuel level gauge, the gray is the fuel pump power, and the black is ground.

Pin letters:

A: blk
B: ppl
C: gry

So the fuel pump should be the outer two connections.

RBob.

 

Alright, so I know what the wires coming FROM the fuel tank are. But the connector that the fuel tank wires plug INTO is flush against the underside of the car, and I still need to know what each terminal is for. I'm getting 8.6V (key on) out of the mysterious middle terminal, and nothing out of the two outside ones.

 

You've lost me. What Bob posted was that the middle terminal has jack to do with the fuel pump. That's just your gauge. It'll vary depending on how much fuel is in your tank so stop measuring that wire and do it to the outside too. Just measure the volts out of the outside 2 wires at that connector that's flush against the underside of the car. He posted what each terminal is for, what's the problem? To check the fuel pump ground, do a continuety test from the body to the black outside wire. If you can't tell which color wire is witch, try both outside terminals, if it beeps that's good and it's ground. Hotwire your fuel pump relay and measure the volts at the pump. If it's hot and at least 11 volts then plug it in and listen for the fuel pump to go on. If it doesn't, rip out the fuel tank and figure out if it's a bad connection inside the tank or a bad pump, done. Now if you're not getting power through those wires then something else is wrong, especially if you've made sure that the relay is getting power. Sorry but I can't really help much more than this, good luck.

 

Alright.....first of all, I owe a big "thank you" to JPrevost and RBob. Thanks for all your help so far, guys and sorry for being a bit of a pain.
That being said...
I tried bypassing the oil pressure switch today, and I finally got 12 volts at the rear connector coming from the "fuel pump power" wire. I also tested the ground wire at that connector, and got a good "beep" from the meter. However, I'm only getting voltage at that rear connector when the oil pressure switch is bypassed. So, after getting voltage to this connector, I reconnected it and tried to see if I could get the pump to prime. No luck. So at this point, I'm imagining that I need a new pump, am I right?
Also, though, do I need a new oil pressure switch? Or is the way I described things the way they should be? I would think that power would have to be getting back there to prime the pump, so that would be before the switch comes into play.