fuel pump power

ok, 95 rodeo...i have power at the fuse/relay(swapped relay with working one) box, but no power at the connection....... anyone please tell me what might be the problem from here??? could the computer shut down power after fuel pump died, and is there someway to reset the computer???????
please oh, god please help!
thanks,
Robert Moller

There is a relay under the hood.

You can always reset the computer by disconnecting the battery and waiting for some time, but I don't recall ever hearing that the ECM shuts down the pump pwr after a pump failure.

When you say there is 'no power at the connection', I assume you mean the connection at the fuel pump itself. Yet, you have voltage at the relay.

The schematic shows that the relay switches the pump on depending on a signal from the ECM (pink/wht wire). Using a heavy gauge wire you could jumper the relay terminals manually (bypassing the ECM signal) to see if the pump gets power.

any chance of a pic of the schematic? i tested voltage at fuse 13.9 something, not after relay.. I than checked voltage at connection on wire about 10inches from tank nothing at all there. i tested horn it worked, swapped relay(horn still worked). turned key to on position and still no voltage at the "connection". Got real cold out (utah is great), so i stopped there and tried to report my progress here. i dont want to run down all that wire if i dont have to.
thanks for youe support!
Robert Moller

The fuel pump doesn't have constant power unless the engine is running. If you are turning on the key, crawling under the car, hooking up volt meter then measuring, you're not getting there in time to see it.

When you first turn on the key, the pump comes on for a second or two to prime the system then shuts off until the engine starts.

The fuel pump doesn't have constant power unless the engine is running. If you are turning on the key, crawling under the car, hooking up volt meter then measuring, you're not getting there in time to see it.

When you first turn on the key, the pump comes on for a second or two to prime the system then shuts off until the engine starts.


That's a good point. You should be having someone else turn the key while you measure the voltage at the pump. If you need to retry, wait a minute or so before turning the key again. On many vehicles, the ECM will not prime the pump again for another 45 secs or so.

haha! now thats good info! that will help me so much. thanks both of you! I have to work tomorrow so i will post results when i try in the afternoon. Again thanks, and anyone else or any thoughts on.

1. have wife turn key
2. Measure voltage
3. if voltage is there, plug fuel pump back in
4.????wait 45 seconds to turn key again????
5.????repeat #4 many times to prime?????

any help would be great!
again thanks for youe time already spent on my problem
Robert Moller

haha! now thats good info! that will help me so much. thanks both of you! I have to work tomorrow so i will post results when i try in the afternoon. Again thanks, and anyone else or any thoughts on.

1. have wife turn key
2. Measure voltage
3. if voltage is there, plug fuel pump back in
4.????wait 45 seconds to turn key again????
5.????repeat #4 many times to prime?????

any help would be great!
again thanks for youe time already spent on my problem
Robert Moller

I wouldn't worry about repeatedly trying to prime the fuel pump. I'm just saying that if you need several tries to verify the voltage, just know that the ECM will time out at some point after repeated tries. I remember JLEMOND (isuzu instructor/guru) saying that after 2 or 3 repeated turns of the key and/or if you leave the key in the on position for much longer than 2 or 3 seconds, the ECM times out circuit for up to 45 seconds.

If you get a voltage when turning the key, it will only last for the 2 or 3 seconds of priming, then come back down. Next, have wife crank the engine, the voltage should stay on during cranking.

If you have voltage, then hook up the pump to see if pump works. It is not uncommon on first gens to have bad electrical connection at the wiring harness where it connects to the pump. Try wiggling wires while wife cranks engine if pump doesn't power up.

ok, tested voltage at connection, when key has just been turned....only 9.6 volts! how could this be....i also plugged the pump back in and did not hear anything, but that could be because of low voltage, again any thoughts on where to start looking?
thanks again,
Robert Moller

ok, tested voltage at connection, when key has just been turned....only 9.6 volts! how could this be....i also plugged the pump back in and did not hear anything, but that could be because of low voltage, again any thoughts on where to start looking?
thanks again,
Robert Moller

With the key turned, you should be getting battery voltage (around 12.5 volts). Check the voltage at the battery, then at the fuse, then remove the relay and check the voltage there. Maybe your battery is discharged a bit with all the testing.

thats what i thought after i read what i wrote, de da de.... anyway, to cold outside to do anymore tonight. i will start over again in the morning... would hooking jumpercables up b4 i start all this be a good idea? again thanks for your input!
Robert Moller

going to get started this morning, any thoughts on the best way to see if the fuel pump is getting fuel to the engine? where should i check? if this helps, everytime i have opened the gas cap there has been plenty of pressure, i would assume the pump was building that pressure in the plethra of times i have turned the key to check on the pump. how long should it take for fuel to reach the engine from the pump if it is working properly?should i disconnect the fuel line after the fuel filter? any help would be great!!!! thanks again!

Robert Moller

Do you have a Schraeder valve in the fuel line near the fpr? You can get a cheapo fuel pressure tester and check it out.

going to get started this morning, any thoughts on the best way to see if the fuel pump is getting fuel to the engine? where should i check? if this helps, everytime i have opened the gas cap there has been plenty of pressure, i would assume the pump was building that pressure in the plethra of times i have turned the key to check on the pump. how long should it take for fuel to reach the engine from the pump if it is working properly?should i disconnect the fuel line after the fuel filter? any help would be great!!!! thanks again!

Robert Moller

Checking for fuel at the fuel line after the filter is the only easily accessible point I'm aware of. Didn't you say that you installed a new fuel pump? Are you getting constant voltage while wife cranks the engine? If fuel is coming out at filter, the pump is probably working ok. Fuel pressure check at the schrader valve, as FL 3.2 suggested, would be great if you have a guage.

..., everytime i have opened the gas cap there has been plenty of pressure, i would assume the pump was building that pressure in the plethra of times i have turned the key to check on the pump. this doesn't indicate anything about the fuel pressure. it indicates that the fuel cap and other components of the evap recovery system is working and holding pressure (not leaking to the atmosphere).

how long should it take for fuel to reach the engine from the pump if it is working properly?should i disconnect the fuel line after the fuel filter? any help would be great!!!! thanks again!

Robert Moller you can disconnect it there, and you will at least see if fuel is being pumped, and you can measure the other fuel pump spec -- fuel *volume*. careful.

you might as well go buy a fuel pump pressure gauge set, and hook it up to that valve -- projects are always the best rationale for buying tools....

//bc

YOU GUYS ROCK!
Thanks,
Robert Moller