Help confirming Bad Fuel Pump
Help confirming Bad Fuel Pump Car is a 1993 Firebird with the LT1 and a T56. Took car out of storage and drove for 10-15 miles and was fine. Went to restart and it wouldn't start. I put a fuel pressure gauge on it and here were the results.
1st time, key on, went to 25psi. Car then started but ran poorly, could put no load on or it would die out. Pressure was bouncing all over the place from 25-45 psi on the gauge very quickly.
2nd time, key on, went to 15psi. Car started again and ran poorly but then smoothed out for a few second, then started running poor again. Pressure gauge was again bouncing all over the place from 25-45psi rapidly.
3rd time, Key on 0psi, wouldnt start
4th time, Key on 0psi, wouldnt start.
I have replaced the fuel pressure regulator recently. Im pretty sure this is a fuel pump issue just want confirmation. Is there anything else that can cause the fuel pump to act this way? Bad sensor somewhere? Thanks
1st time, key on, went to 25psi. Car then started but ran poorly, could put no load on or it would die out. Pressure was bouncing all over the place from 25-45 psi on the gauge very quickly.
2nd time, key on, went to 15psi. Car started again and ran poorly but then smoothed out for a few second, then started running poor again. Pressure gauge was again bouncing all over the place from 25-45psi rapidly.
3rd time, Key on 0psi, wouldnt start
4th time, Key on 0psi, wouldnt start.
I have replaced the fuel pressure regulator recently. Im pretty sure this is a fuel pump issue just want confirmation. Is there anything else that can cause the fuel pump to act this way? Bad sensor somewhere? Thanks
TECH Veteran
Joined: Dec 2008
Posts: 4,147
Likes: 62
From: Little Rock, AR
The pump does not rely on any sensor to run. Can you get fuel pressure using the fuel pump prime connector? I'd verify power is getting to the pump before assuming it is a pump issue (might be the relay).
Joined: Jul 2007
Posts: 2,861
Likes: 4
From: Ringoes/Flemington, New Jersey
shbox is dead on. It is probably a bad fuel pump, but you can jump the relay and check for power at the relay. if you turn the key and cant hear it, the pump is probably dead 
.
Good luck! also, make sure to check for power at the connector under the car on the driver's side to verify the power is getting close to the pump. SHBOXs website has great stuff
. Good luck! also, make sure to check for power at the connector under the car on the driver's side to verify the power is getting close to the pump. SHBOXs website has great stuff
TECH Veteran
Joined: Dec 2008
Posts: 4,147
Likes: 62
From: Little Rock, AR
On your car that actually bypasses the relay, but is the quickest way to see if the pump is running. If it runs, back up to the relay and continue testing.
OK, I tested the prime connector. The pump got to 30 psi and that was it. I tried several times and thats all it put out. I will go back to the relay and see what happened then. What pins do I jump?
TECH Veteran
Joined: Dec 2008
Posts: 4,147
Likes: 62
From: Little Rock, AR
From the relay, you just need to see if you are getting 12v out to the pump.
Schematic here.
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As far as I know the fuel filter is original to the car. When I did the prime connector I heard the pump kick on at first but then when it got to 30 I couldnt hear it anymore. Almost like it turned off. Ill jump the relay tomorrow, see what happens.
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Im pretty sure the pump is bad but I want to check the relay and filter just to make sure. I have a brand new airtex pump to put in but if I don't have to that would be easier. I am bad at reading wiring diagrams, which connector do I jump on the relay?
TECH Veteran
Joined: Dec 2008
Posts: 4,147
Likes: 62
From: Little Rock, AR
If you want to test it without removing anything, you don't jump anything. Better to test as is, before you disturb anything, IMHO. You turn the key on and see if you get 12v on the grey wire. Note that it will only energize for about 2 seconds, then go off, if the engine is not started. You can test this at the plug under the car going to the fuel pump and not even have to open up the panel to the relay.
http://shbox.com/1/fuel_pump_wiring.jpg
http://shbox.com/1/fuel_pump_wiring.jpg
FWIW, check how well the power wires are crimped to the connectors at the rear floor pan bulkhead connector/plug. A couple of years ago, one of the power wires came loose on my car, and the car died on me. It was poorly crimped right from the factory, and after 16 years of driving, it finally worked loose, and lost contact.
ok, So I go under the car, unplug the pump at the connector and then see if the gray wire port energizes when I turn the key? That will tell me that the relay is working as it should and that the issue then lies in either the pump or the wiring to the pump? If I am not getting power there then I should replace the relay and retest?
TECH Veteran
Joined: Apr 2008
Posts: 4,985
Likes: 112
how long was it stored?
was there fuel stabilizer used?
replace the filter
once you confirm you have 12v going to pump (replay would be working) and FP is still low after you replace fuel filter....you need to replace pump
was there fuel stabilizer used?
replace the filter
once you confirm you have 12v going to pump (replay would be working) and FP is still low after you replace fuel filter....you need to replace pump
Replaced Filter and checked wiring and still no pressure. I swapped pump out and it is working as it should.
However, the wiring at the top of the tank that connects the sending unit and pump to car is very loose and I am afraid that over time the connector inside the tank will work its way loose. Is there anyway to help prevent that or to replace that wiring?
However, the wiring at the top of the tank that connects the sending unit and pump to car is very loose and I am afraid that over time the connector inside the tank will work its way loose. Is there anyway to help prevent that or to replace that wiring?
