This 1988 S10 Blazer w/4.3 & 700r4 has been an ongoing project for me for about 8 mos. now. I love this little rig but she's really got me scratching my head now. I had to swap in another motor recently. Got it all buttoned up did the standard check list and prayer before hitting the key for the first time and she fired right up. I let it sit and idle for a few and checked for leaks, watched the gauges, ect. She went up and down the drive with no issues and I thought all was good. The next day I went to pull it out of the garage and when I hit the key it just clicked. I thought no biggie, something is draining the battery. I disconnected the battery and checked it with a multimeter and it read 12.4 volts. Here is the strange part, as soon as I reconnected the battery I heard the fuel pump running. The key was not even in the ignition! I understand that there are a few different things that will STOP a fuel pump, but I have no idea why it is running whenever power is supplied to the vehicle. Any help would be appreciated. Sorry for the long post, too much info. is better than too little. Thanks again, and have a good one.

 

There is a wire that runs straight to the pump (fuel pump test port) but if it didn't do it before it's probably not your problem.If somehow you've got 12v connected to it though it'll run all the time.

 

Yes, hanging off your fuel pump relay is a wire thats not connected to anything... Its not supposed to be, its a direct power lead for testing purposes. You may have found that wire hanging and hooked it up to power when trying to figure out what its supposed to be for... Ill try and snap you a photo of mine to show you what we are talking about.

 

Thank you for the replies! When I did the engine swap I marked everything so I wouldn't get myself all screwed up when it came time to hook it back up. As I said in the first post, I had it running and moving up and down the driveway. When I shut it down the pump wasn't running. I've read in my manual that the ECM controls the fuel pump as far as when to run and stop and reading pressure values. Do you think it's possible I've fried my ECM? With this and the no-start condition I'm starting to think maybe that's it. As always, any ideas are appreciated. Have a good one.

 

Check your your oil sending unit. The oil sending unit provides back up power to the fuel pump if the relay fails. I replaced my oil sending unit with one from O'reillys and the the pump would stay running. I returned the oil sending unit and got one from NAPA. The easy way to check would be to disconnect the wire from the oil sending unit to see if the pump quits running. I have not had any issues since I replaced the Oil Sending Unit.

 

Thanks Mr. Vls that is definately worth a shot. I'll keep you posted. Have a good one!

 

Whoa we have that? Get us a picture. I dont remember seeing a extra wire in any of my 1st gens. Then again i never mess around in that area.

 

O.K., sorry for the delay, work. I tried the oil pressure sensor with no change but I'm wondering if I don't have a bigger problem. I tried it after tinkering with a few things and noticed that when I turn the key as if to start it both of my directional lights (blinkers) in the dash light up until I let the key go. I'm thinking of swapping the computer with the one from my donor to see what that does. Here's another question though, My current ECM is from an '89 while the one from my donor is an '88. Will this be a problem or if the numbers on the tag match I have no worries? Thank you for all the replies. Have a good one!