1994 S-10 Blazer 4WD Fuel Problem--Help

Last night I came home from a trip and was backing the vehicle up and it just quit. It would not crank up. I took a test light and checked the power to the fuel pump and there was none. This morning I went out and I turned the ignition and I heard the fuel pump kick in and the vehicle cranked up for about 10 seconds and then shut down as it did the night before. I again took the test light and checked for power at the pump--nothing. I had someone cycle the ignition switch and I briefly get power at the pump--just briefly. I have change the fuel pump relay---stil a problem. Can anyone tell me what activates power to the pump?Anyone have any ideas?

at this point your fuel pump is shot. The second it gets warm it dies...(in seconds)

at this point your fuel pump is shot. The second it gets warm it dies...(in seconds)

Thanks for the reply. I have disconnected the pump at the pigtail and I still get the 1 to 2 second 12 volts and then it drops to 0 (zero). If I have disconnected the fuel pupm shouldn't I have a constant 12 volts? The fuel pump is out of the equation at this point--I think. Any assistance is greatly appreciated.

That is normal. The power comes on for about 2 seconds when you initially turn the ignition switch on then the power to the pump is interupted until the engine is running. With the engine running you should have a constant current, but when it's not, it only stays on about 2 seconds.

That is normal. The power comes on for about 2 seconds when you initially turn the ignition switch on then the power to the pump is interupted until the engine is running. With the engine running you should have a constant current, but when it's not, it only stays on about 2 seconds.

Thanks for the info. I'll change the pump tomorrow and hopefully that'll take care of the problem. I'll let you know. BTW, I was reading somewhere that new fuel pumps do not require the pulse. Is this correct?

I have heard conflicting views on the pulsator issue. I also have a 94 that I recently replaced the fuel pump on. It came with a hose instead of the pulsator, but I left the pulsator on that was already in place. You can check the pressure at the shrader before you start changing parts though because there are many other things that can cause fuel problems on this model. Even the pressure test won't eliminate them all, but will give you some idea of where to start. You should have 55-60psi at the shrader when you turn the key on without starting it. Good luck!

Thanks for the info. I'll change the pump tomorrow and hopefully that'll take care of the problem. I'll let you know. BTW, I was reading somewhere that new fuel pumps do not require the pulse. Is this correct?

OK, I changed the fuel pump and still the new one does not work. It does nothing. Any suggestions??

I have heard conflicting views on the pulsator issue. I also have a 94 that I recently replaced the fuel pump on. It came with a hose instead of the pulsator, but I left the pulsator on that was already in place. You can check the pressure at the shrader before you start changing parts though because there are many other things that can cause fuel problems on this model. Even the pressure test won't eliminate them all, but will give you some idea of where to start. You should have 55-60psi at the shrader when you turn the key on without starting it. Good luck!

I changed the pump today and the new one still does not work. What activates the fuel pump? Is it the ignition switch? Someone told me the MAP Sensor may be bad--Any Suggestions??

you should have a relay, (on ,my 96 it's in the glove box) there are 3 in there behind a black plastic cover, try swithing each one out with a known good one....good luck

you should have a relay, (on ,my 96 it's in the glove box) there are 3 in there behind a black plastic cover, try swithing each one out with a known good one....good luck

I found two relays for this 1994 on the firewall drivers side right above and behind the brake vacuum booster. I purchased a good fuel pump relay and have switched them both. I checked behind the plate in the glovebox and there is nothing there. I checked for power at the relay with a test light and I get 12 volts of power for about 2 seconds. Same thing at the fuel pump pigtail. So, its got to be something before the relay---what actiates the relay?

Thanks for everyone's input.

I found two relays for this 1994 on the firewall drivers side right above and behind the brake vacuum booster. I purchased a good fuel pump relay and have switched them both. I checked behind the plate in the glovebox and there is nothing there. I checked for power at the relay with a test light and I get 12 volts of power for about 2 seconds. Same thing at the fuel pump pigtail. So, its got to be something before the relay---what actiates the relay?

Thanks for everyone's input.

Have you actually checked fuel pressure? When you replaced the pump was it for the CPI or TBI motor? Check your fuel pressure. If it's still low you either got the wrong fuel pump or the CPI and/or nut kit blew. If you're running TBI start checking your injectors.

Have you actually checked fuel pressure? When you replaced the pump was it for the CPI or TBI motor? Check your fuel pressure. If it's still low you either got the wrong fuel pump or the CPI and/or nut kit blew. If you're running TBI start checking your injectors.

It is for the CPI motor. I took in the VIN number (W) and matched it up in the parts section. No, I have not actually checked the pressure of the system. I did disconnect the fuel filter and cycled the ignition switch and there was no fuel coming out of the fuel line whatsoever. You mention CPI or nut kit. What exactly is that? Maybe thats where I need to start looking.

Thanks again for all your assistance.

You really need to check the fuel pressure at the shrader valve on back of the upper intake. The CPI (fuel injector) and the nut kit (inbound/outbound fuel lines) are underneath the upper plenum.

I know it seems like I'm just throwing stuff out there but how is the ground to the fuel pump...

I know it seems like I'm just throwing stuff out there but how is the ground to the fuel pump...

I took the ground off the frame, wire brushed it, and rebolted it down. I took a test light and reversed the leads and checked the ground using the license plate light. It seemed to be good.

All I can say is that all suggestions are great to have. Keep them coming.

Check for 12 volts @ pcm pin #E16 that will be the blue plug, orange wire. That is the battery power to pcm and it is always hot. If you have intermittant power at that pinout or there is no power at all, it is more than likely that there is a bad splice in that circuit. If you have 12 volts @ fuel pump relay but no pwr @ pcm check the big wire loom behind the ac pump going to firewall (passenger side). There is a splice there that connects fuel pump relay and oil pressure sending unit and then goes to the pcm. Oil pressure sender and fuel pump are on this circuit and that splice gets corroded causing intermittant power or total loss of power. Haynes or chilton manual won't inform you of that. Remember, orange wire, big loom. If you find the problem to be something else, keep in mind what I have described for future reference. Hope this can be of help now or later. By the way, fuel pump relay along with horn relay is behind dash right above the transfer case shifter. The door and light buzzer is there too.

Oil pressure switch could be bad in 1994 the power goes to the oil pressure switch and if the switch is bad it will cut power to the pump

Have you checked the coil, modulator, and pickup? My 94 Blazer 4.3 Vortec had similar symptoms. After replacing many parts (all new fuel related components) I found the defective part to be a bad pickup. Once replaced the problem disapeared. Mine would start and run until it got hot, then shut off until it cooled, at which point it would start right up. Not sure if there is any way to actually test the pickup, but you can test the coil with a voltmeter, and the modulator can be tested at O'Reilly's once you remove it. That would be something worth checking if you haven't already.