I have 95 blazer s10 4.3l that I changed the fuel pump and fuel filter on about 4 months ago, now the truck is doing the same thing again and I am wondering if there is some dome diagnostics I can go through before I drop the tank again. When the truck is cold (first thing in the morning) it fires right up, runs for about 30 seconds and then dies, and will not start again unless you let it sit for half the day. It runs really nice for that 30 sec then it stalls like someone shut the key off (doesnt sputter at all). I do not hear the fuel pump kick in after the truck stalls with the key on, although it does kick in on a cold start. I know everyone will say replace the fuel pump but, I read that there may be a way to diagnose this a little better (I hated changing the last pump). Voltage readings, ground issues, relay etc. I just dont know where to start these procedures. Is there a schrader valve on the 95 s10 where I can test the fuel pressure, if so where is it located? I heard that someone had similar symptoms and it was computer related. I guess I just want to be positive it is the fuel pump before I start anything.

Thanks
Trev

 

Not sure what the prob. might be but there is a valve to check fuelpressure on the drivers side at the back of the intake.

Good luck

 

The way to check if it is the pump or the computer is to start it, let it run and stall, then check for voltage at the fuel pump relay. Pin 85 should be 12v trigger from the VCM, Pin 86 is the ground for the coil side, Pin 30 is the 12v source for the fuel pump through the fuel pump fuse, and Pin 87 is the wire to the fuel pump. Pin 86 is always connected to ground. When the VCM (vehicle control module - aka PCM) sends a signal to the relay, it energizes the coil to pull the contacts of pin 30 and pin 87 together to power the fuel pump. If it is indeed something pcm related, you shouldn't have 12v to pin 85 after the truck dies.

This sounds very much like a security feature gone bad. My old intrepid would run for 30 seconds, then shut off whenever you tried to start it with the alarm still enabled. That car didn't have a resistor in the key or anything, just an alarm that was activated by the locking of the doors, but some sensor was going bad so that even if you unlocked the doors, it may not disarm the alarm.

Does your key have a chip in it? It should be on the part that goes into the ignition switch. If it does, maybe try cleaning its contacts with some light sand paper. You may have to do the security relearn, which off the top of my head I cannot remember right now, but I can look it up when I get home tonight.

If that doesn't fix it, I'd be inclined to say that your ignition switch is bad and needs replacement. They can cause some pretty weird and seemingly unrelated problems.

 

Thanks for the reply, where is the vcm/pcm located? Pin 86 should have 12v before or after the truck stalls? It does have a security alarm but I dont really know much about it other than I have to push the unlock button to start the truck, so if you have relearn instructions that would be cool. There is no chip in the key.

 

Is it a factory alarm? If not, then you may have to relearn the remote. The remote obviously works on the doors, but if the security system isn't disarming, it will kill the ignition, fuel pump, or both.

Pin 86 should have 12v when you simply key-on (not start, but on). To check this, you have to pull the relay (which will shut off your fuel pump), flip the relay over to see which pin is 86 and then test the corresponding cavity. If you aren't getting power there after the truck dies, then something is amiss with the security system. To get around this, you can remove the relay and put a jumper wire (small length of wire and some spade terminals) jumped across pins 30 & 87.

BE AWARE that the fuel pump will run the entire time that this jumper is in place. If you do not remove it, it will drain the battery.

This is ONLY recommended to make sure that the fuel system is the only system affected by the problem.

 

Did ya put gass back in it?