93 s-10 blazer fuel pump problem

93 s-10 with 4.3 vortex

I can drive the blazer and it runs fine but when you shut it off, it will not start again until it sits for about an hour.
I have replaced the fuel pump relay and the oil pressure switch.

I went through this myself this past winter. Thought I had a fuel problem, and it got worse. Turned out to be a bad ignition module. It would fire at random. Might check that out among other things such as EGR valve (maybe stuck) or bad regulator (under plenum).

One thing I forgot was when it will not start you do not hear the fuel pump when you turn the ignition on. When I wait about an hour you will hear the fuel pump and it will start right up.

One thing I forgot was when it will not start you do not hear the fuel pump when you turn the ignition on. When I wait about an hour you will hear the fuel pump and it will start right up.

I forgot to mention this before, but would strongly advise you to buy a fuel pressure tester to properly check for pressure, pressure leaking off, etc. I wasted over $150 before figuring out what was wrong. Would have saved myself a lot of trouble with one. I did buy one later. These engines have a high pressure, takes 55-60 lbs to start. Since the fuel pump does not always make a noise it is best to check for pressure, and possible bleed off. It is possible that the pump is OK. but the regulator is not. Could be leaking in plenum. A lot of discussion on this in the Blazer forum and the S-10 forum. If you get high pressure and it does not leak down then you need to check ignition.

Checked the fuel pressure when the blazer was cold and it was at 54 lbs. when the pump cut off Blazer starts right up. Drove for about 20 minutes turned it off it would not restart. Hooked up fuel pressure gauge no fuel pressure. I have replaced the fuel pump relay and the oil pressure switch. Is it fuel pump or something?

Sounds like a fuel pump problem to me. One more thing that might help your troubleshooting. On my 93, there is a open connector (green?) in the harness back by the firewall on the left center as looking in from the front. It goes to the high side of the fuel pump. It should show 12V when the pump is receiving voltage to run. It should be 12V for a couple seconds after turning on the key, and also when the engine is running. If you are sure it is the fuel pump, you can also carefully jumper it to 12V to force the fuel pump to run (for testing).

93 s-10 with 4.3 vortex

I can drive the blazer and it runs fine but when you shut it off, it will not start again until it sits for about an hour.
I have replaced the fuel pump relay and the oil pressure switch.

My somewhat educated guess is that the ECM is bad. The reason I say this is I had the same problem - I'd turn my '87 S-10 off and it wouldn't restart. I initially thought it was the fuel pump so I changed it, and the filter, to no avail. And like you, it would start up after sitting for a while, sometimes overnight. Often I'd get out, pop the hood, and look at things, touch some wires, and get back in and it would start! I went through at least 6 months of that... and then, one time it didn't start after sitting. It sat for several days without starting and none of my "mechanic" friends really knew why. I did notice about this time that the fuel pump wasn't pumping when I turned the iginition on... After looking online for wire diagrams I found a halfway decent one at autozone.com. Enter your car type and click the Vehicle Repair Guide link on the right side of the page. I checked for opens in all the wiring paths I found none. I scraped the oxidation off the fuse leads, scraped oxidation off anything I could find to see if maybe it was a bad ground or something... I shorted the fuel pump relay plug straight to the fuel pump to see if that would make the fuel pump work... nothing... Then I went to partsamerica.com and clicked on Reliability Rating, under "Do It Yourself" and found that S-10's seem to have a problem with the ECM (not the Ignition Module but the Engine Control Computer or Electronic Control Module, found under the passenger side dash). So I replaced it and VIOLA! No problem... Everything was perfect. That was March 5th this year... About four weeks ago the same thing happed again... I went to start it right after parking for a minute and it wouldn't start. Left it over night and it started right up again. Then, on July 3rd, I went to church and came out and it wouldn't start. I live in a small town and to get another ECM takes 4 days through Kragen Auto (aka Parts America) - unless the wrecking yard has one and you don't really know if it's any good... so I went through everything again, tore the dash apart looking for terminal junctions, and regrounded everything... checked continuity... Anyone have a 10lb sledge hammer? I don't know if something is causing the ECM to go bad or if they are born bad. Some irony - the distructions for the ECM say to troubleshoot for the cause of the problem prior to installing a new ECM... or you'll damage the ECM... well, what if it is the thing that is BAD! I just ordered another one and am waiting for it.

Just thought I would let everyone know that it was in fact a bad fuel pump.
Thanks for everyone's input.

Having same problem and im replacing the pump and sending unit (wiring in it also claimed to be problem elsewhere) this weekend.

Also as far as the ECM and the fuel pump. It would still do the inital loadup when key is on regardless.