Geekium

Hi there, first post here after lurking while waiting for a seller. Finally got my hands on a nice '91 Bird thats been sitting for a year covered/garaged.

Learning as I go here, based on troubleshooting steps in some other threads I've found I have successfully tested for spark (good) and now and looking at fuel. Pump does not prime or send, and I read that at the fuel pump relay the red wire should be hot at all times. It is NOT. Checked (and swapped for known good) fuse and still no dice. Trying to figure out where to go from here.

update: New relay has been installed and the relay clicks over on key turn. Currently no voltage even with key turned at the injectors on either wire.

Schurkey

Time to buy a REAL service manual for your vehicle. Often available on eBay for half-price or (sometimes much) less.

In the meantime, check ALL the other fuses.

Seems to me that my '92 Lumina powers the fuel pump fuse via a separate wire with it's own fusible link, attached to an auxiliary battery stud near the battery. If that wire was removed from the auxiliary stud, or if the fusible link were popped, there'd be no power at the fuel pump fuse.

Geekium

Yeah I've got one in route. Won an auction for $25. I'll keep plugging away at this till it gets here, honestly whats bothering me most is no power to the injector terminals. I know they fire by being pulled to ground so there's a wire on each connector that should be hot at all times. Neither are hot even when the key is turned.

RBob

iTrader: (1)

In the fuse block (drivers side above your feet) are two fuses for the injectors: INJ1 & INJ2.

The fuel pump relay gets power from an inline fuse under the hood. It varies between the 'Birds and Camaro's, but it is usually along the passenger side of the car. IIRC, the Firebirds have this fuse near the battery.

RBob.

Geekium

Yeah I've checked all three fuses. They all test good. However there's no power going to the fuel pump fuse nor the injector fuse, Which I find odd. Does that basically just mean I've got a shorted or chewed up wire somewhere?

RBob

iTrader: (1)

Chewed up wire someplace, the inline fuse under the hood is connected directly to the battery positive terminal. It supplies power to the FP relay and to the ECM.

The INJ 1 & INJ 2 fuses get power through the ignition switch. Which likely means that a fusible link at the starter it bad or the ignition switch is bad.

RBob.

Geekium

After a full day on the car, with new tools and more info, I've narrowed down all of my problems to one single thing. The injectors are now firing, the fuel pump relay works, all fuses and circuits are confirmed working.

I ended up all the way down at the fuel filter, and took it off to test if the pump was sending fuel at all. When I jumped the fuel pump relay to get the pump going it ran and I don't have anything to go against but the flow from the pump to the filter seemed incredibly weak.. id estimate it would take 5-10 minutes to fill a water bottle with gas at the rate it was flowing. I replaced the filter since I was already down there (made sure to put the output side correctly!) and went up to the throttle body and disconnected the fuel line and attached a rigged up catch bottle to it. Jumped the plug, pump came on, fuel never reached the engine bay. No leaks.

After all of this I disconnected the side of the filter that goes to the engine and only a dribble of fuel came out.. almost as if the pump couldn't even push the gas through the filter.

I'm taking all of this to mean the pump is dying?

Schurkey

ONLY if the pump is getting proper power and a good ground. (And then, only if the fuel filter sock on the end of the pump isn't plugged, and if the hose or damper connecting the pump to the hanger tubing isn't ruptured)

You could easily have a "weak" pump because the wiring or the wire connections are corroded. Low voltage to the pump = crappy pumping. Poor ground to the pump = crappy pumping.

The wire harness INSIDE the fuel tank is a known problem-area due to corrosion of the connectors at the ends of the wires.

The only GREAT way to test fuel pump wiring is with a voltmeter, an ammeter (inductive current probe) and a digital oscilloscope. With that equipment, you can test fuel pump voltage as near to the pump as practical, you can test fuel pump current draw (average, and comparing armature bar-by-armature bar), and you can verify fuel pump RPM.

Most folks don't have access to an oscilloscope. Many folks don't have access to an ammeter of any sort. All that leaves is voltage testing. Better than nothing, but not altogether good.

When I checked fuel pump power on my Luminas, I discovered that GM was using under-sized wire throughout the whole fuel pump harness. They used 16 gauge wire where 12 gauge would be required based on current flow and wire length. There was voltage drop EVERYWHERE. There was an entire volt lost on the power side, and another volt lost on the ground side. If the alternator was putting out 14.2 volts, the pump was only running on 12. GM needs a bitch-slap for that.

Geekium

Thanks for that, I admittedly hadn't thought of that. I'll be able to check closer to the pump later this week but before work this morning I checked voltage at the relay going to the pump and it stood at 12.25v. I haven't been able to see on any wiring diagrams where the pump actually draws power from (beyond a fuse) but I'd assume I should clean the aux. Battery terminal connections near the battery. I'll report back once I've checked voltage at the connector before the pump just above the rear axle and cleaned all connections.

TTOP350

iTrader: (8)

Could also be a bad pulsator or rubber hose from pump to hard line in the tank.

DynoDave43

iTrader: (11)

Don't our car have a connector under-car, in the tunnel for the axle, clipped to the back wall of the back seat? Hard to describe, but I seem to recall reading about it, and it's potential for corrosion.

Geekium

Sure does, found it while I was hunting wires down. Gave both sides a good brushing after I tested to see if power was getting that far. Have to go back now and test how much power is making it that far.

DynoDave43

iTrader: (11)

Good catch on your part Geekium. You're approaching this the right way. You'll get there.

Geekium

Alright. So full voltage is reaching the pump, and there's a good ground on the whole circuit. I get continuity from the relay all the way back to ground. Pump turns on, does pump some gas, but like I said above, its a trickle. Doesn't seem too loud, is barely audible from the drivers seat. At this point either the strainer is clogged or the pump is in fact dying I'd imagine. Before I go and pull the tank, is there anything I can try to run through the system with the gas to break down deposits/crud on the strainer and pump in there as a last ditch effort?

Schurkey

Unless you've pulled the pump out, you don't actually know that the voltage is reaching the pump. You could have wire-harness or connection problems inside the tank.

You've ruled-out problems farther up the wiring harness, though.

"Continity" isn't enough. You could have excess voltage drop, and still have continuity.

You're probably right, I expect the pump is faulty...but until you do amperage testing, with an oscilloscope, you don't really know what's happening in the tank. So, yes, your next step is to either locate a digital oscilloscope and a low-amperage probe, or you drop the tank.

Not really. Any grit "broken down" by a chemical would wear the pump and then plug the fuel filter. Mostly, chemicals wouldn't be that effective in dissolving whatever has plugged the strainer.