I have a 95 blazer with w code 4.3. a few weeks ago it failed to start after repeated attempts. It finally started so I picked up a can of starting fluid on the way home. The next day I just got it started in time to get to work using the starting fluid. I checked the forums and found a post saying that if the ignition switch (not the key cylinder) was worn out you could turn it just until it started to turn over (about 3/4 of the way) it would fire. The next day I try it. First try I get a sputter, second try it fires right up. So I drove it that way, maybe three days, then it quit working. No matter how I turn the key. I naturally assume the ignition switch has finally crapped out and replace it. No start. Fuel pump relay is good, I can hear it click on, then off again, but no fuel pump prime. Does the oil pressure switch for the fuel pump also contain the sender? because I have oil pressure readings as I'm trying to start. I wonder if one function could fail and the other keep working? I have recently replaced the fuel pressure regulator (checked the nut kit, not leaking), fuel filter, and used sea foam about a month ago. I have bought a multimeter and a test light, but really haven't ever attempted this kind of diagnosis, any help would be greatly appreciated, Thanks!

 

Assuming you have fuel, and assuming you have compression, the only remaining thing to find out is spark. It sounds like you have enough spark to run it sometimes. Meaning your spark plug/wires/cap&rotor seem to be fine though it could be a weak spark. The first thing I would look at is the Ignition coil. Ohm it out to see if it's bad.

 

During the initial key on, the fuel pump will run regardless of oil pressure. The relay is energized by the PCM to power the pump independent of the oil pressure switch. Once the PCM times out on the fuel pump relay control circuit, the relay will return back to its default position and the pump will be powered by the oil pressure switch.

The pressure switch is internal to the oil pressure sending unit. Both the fuel pump relay and the oil pressure switch get power from the ECM/BATT fuse #3 (20A) in the instrument panel fuse box off the side of the dash. This fuse is powered at all times.

Have you checked the ECM/BATT fuse?

 

I have checked all fuses. So basically I know the pcm is good due to the fact that I can hear the relay close and then open again? If so then I either have a busted fuel pump or the pressure switch is bad (unlikely since I still show oil pressure when attempting to start) So can anyone tell me where I can access the wires to test the fuel pump? Also I have not seen the schrader valve that I've read about for checking fuel pressure. Is this inside the plenum on cmfi engines? Thanks for the replys!

 

Did you actually test the ECM/BATT fuse?

The fuel pump prime connector should be located up near the firewall either somewhere near the fuel pump relay or towards the driver side. You can also directly jumper the pump at the fuel pump relay.

The schrader valve is located off the back of the intake manifold near the brake booster. It can be a challenge to get to.

 

I put a test light to both sides of it and had juice on both. So the prime connector is just like a jumper for testing? I'll try to jump it at the relay (brand new), if it still doesn't prime it should mean a faulty pump.

 

Just jumped the relay with my test light. I have continuity, but the pump still isn't priming. Gonna order one online tommorrow. I guess I'm just going to replace the pump itself and the strainer since the float and sender are working. Any tips? Thanks for all the help.

 

You may want to pull the connector at the pump and test for power back there. You'd hate to replace the pump and end up finding that the main power and/or ground wire to the pump were actually at fault.

You can read up on what others have run into with pump replacements.

 

Ok sorry it took so long to repost. I was waiting on my fuel pump in the mail. Got the tank dropped (dropping the spare tire first is a good idea) I checked the voltage at the fuel pump connector and had someone turn the key for me. Came up with 11.4 volts (acceptable considering my battery needs to be charged. Bout to go to work and then I'll be back on it. let you know what happens!