fuel pump not running when key is turned

[mobzs]

hi every one,

i have a 4.3l, fuel injected, 93 s10 blazer. on my way to work yesterday i stopped at a store. when i got back in to leave, my truck wouldn't start. got out and didn't hear the pump running (mine runs all the time)
i never had a single problem starting it, one turn of the key and it's right there running. after some road side troubleshooting i ended up jumping a wire from the fuse box to the pump connector directly to get it to run.
today, i figured out that the relay is good, all the fuses are good, the wire to the pump is good, the ground from the relay is good, and i have power to the relay. what i don't have is a signal voltage to the coil side of the relay from the ecm/pcm. my question is does the ecm look for something before it gives a signal to the relay or is automatic when the key is turned? any questions just ask.

thanks
mobzs

[tspencer73]

ignition switch fixed mine. I had same problem. not the ignition cylender but black box below it.

[mobzs]

what black box? where was it located? in the steering column, somewhere in the dash. everything else work on the ecm. i thought the ecm could be only partly dead (just that cicuit), but it sounds possible for my case. disscribe it for me so i know what i'm looking for.
thanks mobzs

[tspencer73]

I found that when I turned key to on possition normally when all worked well..dash lights came on and the fuel pump comes on and blazer starts.

When I turned key on and dash lights don't come on and fuel pump doesn't sound blazer doesn't start.

Ignition swithch is located in steering coloum just under where key goes in. should be a 2 by 2 black box.

Not sure if different years have same part but thats what fixed mine.

good luck Troy

[mobzs]

thanks, i'll check it out.

[Macgyver007]

may sound like an odd question but have you looked at the Oil pressure guage. I seem to remember something about the PCM monitering the Oil pressure, if the Oil pressure drops (or the sender goes bad) then the PCM shuts down the fuel pump