Power at fuel pump, but not enough?
 

Hello everyone, I have a 89 Firebird 305 TBI, fuel pump is not kicking on, I replaced the pump and fuel relay, today I used a test like at the pump plug, the tester light came on but very dimly, I assumed it was because of a bad ground, ripped my interior out and sanded the ground nice and shiny, with no luck. After all the messing around. I decided to cut the ground wire off above the tank and re ground it closer to the tank, eliminating any damaged wiring. After doing so. The pump still doesn't turn on when key is turned and car will not start. Any help would be greatly appreciated!

Thanks in advance!

Re: Power at fuel pump, but not enough?
 

Check the voltage up at the FP relay and compare with what you are reading at the tank. Should be close to eachother. If not, the problem is in between. You can keep doing this all the way back to the battery if necessary to find where the weak link in the chain is.

Alternate possibility, though a long shot in this case: Fuel pump drawing WAY more power than it should. Check voltage at the plug when it's plugged into the pump vs. not plugged into the pump.

Re: Power at fuel pump, but not enough?
 

So I have 11.32 volts at the relay, and only 6.75 at the pump, where do I go from here?!

Re: Power at fuel pump, but not enough?
 

Just tested the pump power wire near the drivers seat, beside where the pump grounds out, there too only has 6.75 volts. I think I'm going to need a wiring diagram

Re: Power at fuel pump, but not enough?
 

On the pump wire right before the computer, it had the same 6.75 volts, I'm confused because the sending unit is also not working because the gauge said the tank is over full. Could it be the computer?

Re: Power at fuel pump, but not enough?
 

The ECM doesn't directly power the fuel pump, it just triggers the relay that powers the fuel pump (I believe it does MONITOR the voltage on the FP power wire, though, if memory serves).

On the FP relay the two BIG wires are your power wires. One side takes battery voltage in and the other side sends it down to the FP whenever the relay is triggered. Do you have the same voltage on BOTH of those wires with the relay triggered? You should. Just measure it right up at the relay connector.

Re: Power at fuel pump, but not enough?
 

Thanks for your input! I will test the two bigger wires when I get home today, when the relay is triggered being when the key is turned?

Re: Power at fuel pump, but not enough?
 

Well, yes, for 2 seconds at first key-on to prime the fuel system. Not again until you twist the key into the start position and fire the motor (the ECM needs to see a signal pulse from the distributor before it will activate the FP relay).

You could trigger the relay manually if your engine is currently non-running (provide ground to the trigger wire, exactly as the ECM would).

I thought you already had a method of triggering the relay so you could measure voltage back at the fuel pump? How were you doing it before?

Re: Power at fuel pump, but not enough?
 

Ohh okay, that makes sense now, when I tested voltage at the pump I did so when the key was turned on, maybe I should re test the wire when I have someone trying to crank the engine, or get them to turn the key so I can test it in the first couple seconds.

Thank you!

Re: Power at fuel pump, but not enough?
 

Which wire is the trigger wire, if I'm going to ground it out?

Re: Power at fuel pump, but not enough?
 

Not sure. It's one of the small ones, but if you're not sure, I'd get a wiring diagram. In fact, if you're in this far you should probably have one on general principle.

Re: Power at fuel pump, but not enough?
 

Do you have a link to a wiring diagram by any chance?

Re: Power at fuel pump, but not enough?
 

I got a friend to turn the key while I tested wire at pump for power, still got the same 6.75 volts

Re: Power at fuel pump, but not enough?
 

I think I recall a guy on here posted up thread called something like "Wiring diagrams- I got them all!". Do a search- I think it was only a couple months old. Or maybe that was vacuum diagrams. I forget.

Re: Power at fuel pump, but not enough?
 

There's some wiring diagrams here but I don't know if they have what you need.

http://www.austinthirdgen.org/?pid=19