vonmoldy

Hello I am trying to help my brother repair his 1992 Firebird 5.0 TBI. The motor has stalled out twice when on the highway. The starter will turn over the engine but will not start. I cannot hear the fuel pump prime when the key is turned. He bought a new relay for the fuel pump which did not remedy the problem.
-I disconnected and cleaned the relay connector and fuel pump wire plug back near the tank with electronic cleaner
-I used a inline spark checker to confirm there is spark.
-There are no blown fuses under the dash and the fuse on passenger side next to battery tests ok
-I am reading 12 volts at the fuel pump relay plug
-the battery is reading ok at 12.2v or so after cranking a few times
-I measured resistance at the fuel pump side of wiring and got a reading of .26 kohms or 260ohms
- with key on I measure for voltage at the fuel pump wiring on the car side and got like 6.8v which is weird. I figured it should be 12v.
-hot wired the pump using the relay wiring connector and the fuel pump would not come on.

It is pretty difficult trying to work on a car that isnt mine without a repair manual or anything, but I am thinking the fuel pump is bad but doesn't explain the 6.8v going to the pump. Of course I didnt have a helper so I dont know if the pump gets 12v and then drops to 6 or something after a certain time or not.

Any help will be appreciated.

mmadden55

Pump bad drop tank replace car run. Get the filter while your at it.

vonmoldy

What bit of information makes you think the pump is bad and not suspect the wiring?

PaulyC

6.8v with the pump plugged in or 6.8v unplugged? If you have 6.8 unplugged and 12v at the relay that could be an issue but I agree with mad, sounds like you farted out a pump.

OrangeBird

iTrader: (1)

You say "with the key on I measure for voltage at the fuel pump and got 6.8 volts" . You do mean during the initial key on two second prime , yes ? You DO need a helper to turn the key from off to on to check the pump voltage , remember the pump only runs for two seconds when the key is first turned to prime the system and it won't run again TILL THE ENGINE STARTS ! If your pump is mechanically bound up (stuck) it will cause an excessive voltage drop through the painfully thin wiring these cars are wired with . Now , approx 7 volts may sound low , but you said you ran power from a different source to the pump and it still wouldn't run , these two indications are why the other respondents told you your pump is roached . Also of note here is that the oil pressure switch is in parallel with the relay to run the pump , I'll enclose your engine wiring diagram to help you understand the circuit's functioning , the detail you seek is at the top center of the drawing , click twice on it to see an enlarged view ......

vonmoldy

I measure at the pump end of the wiring with the key left on. I will have to test again with a helper keeping in mind the 2 second prime. I didnt run power from a different source I just used a jumper from (if i remember correctly) the orange wire on the relay wiring plug to the gray wire and the pump would not run.

vonmoldy

6.8v at the fuel pump wiring plug riveted to the sheet metal body near the fuel tank right above the rear axle differential. Should there be power at all after the 2 second fuel pump prime when the key is on?

PaulyC

Nope, make sure you are testing the grey wire to ground on C313 with the relay jumped. You should see battery voltage (+/-12V) at the relay orange, grey and the grey at the rear connector. If you do then make sure the contacts in the two connector halves are clean and plug it in. If still no dice, its tank drop time.

vonmoldy

Ok will do. Thanks a lot for the reply and everyone's help.

vonmoldy

I just wanted to say thank you to all who have helped so far. I was able to use PaulyC directions and verified I have 12 volts at either end of the fuel pump wiring. So good thing I have a fuel pump on hand and am in the process of dropping the tank and replacing the pump. Without that little detail of testing voltage after jumping the relay end of the wiring I would have just had to guess.

I will report back when I can see if the new pump starts.

Thanks again I really appreciate your help.

vonmoldy

So sorry for all the posts but, the fuel pump got back in and everything buttoned up. First turn of the key and it started right up. Problem totally fixed. Just need to replace the leaky heater valve now. Thanks again people!

GeneralDisorder

iTrader: (1)

Yeah bad fuel pump's are one of GM's most common failure items all through the 80's, 90's, and 00's. I just did a 96 Blazer last week. I'm not even a domestic specialist and I've done dozens of (mostly GM) fuel pumps over the years. Almost never replace a Japanese fuel pump for actual failure. And even though they almost never fail, they still put in an access panel to get at them from under the seats. GM never learned this I guess.

PaulyC