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Fuel pump humming and truck is turned off?

jeff in co

jeff in co

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So my daughter has been driving the Blazer and when I got home tonight, I walked by and heard a humming noise around the rear end. Turned the key on and off.....kept on humming.

The fuel gauge was almost empty so I figured I'd just put some gas in it and see what happens. Put in 15 gallons and drove home. Turned truck off and came back 2 minutes later....still humming.

Am I correct to assume it's a new fuel pump?

dang! :rolleyes:
 
seems you have a problem with your Keyed On source

it shouldn't be on at all, priming or not, with the key off :(
 
Are those pumps switched with a relay?
 
I just went out after 2 hours of it sitting there....it's still humming away. Keys out of ignition, truck off and doors locked.

I hope the battery isn't dead tomorrow morning! :frown1:
 
K85 Octane said:
pull the fuse for now
Click to expand...

Thanks for the tip. :waytogo: I pulled the fuse last night, re-installed this morning and good to go. Started right up at (-4 degrees). I'm sure the battery would have been dead if I let it run all night, so thanks!

Drove to work and then pulled the fuse again. It's suppose to warm in the next few days....
 
I'm thinking the oil pressure switch is screwing up.

ECM is what controls the prime/relay, for it to keep running based on the relay, something would have to be wrong there, and it would SEEM unlikely for it to be an ECM issue.

Easy test, when it's doing it, pull the fuel relay connector and see if it stops. If it'd doesn't, it's the oil pressure switch.

These never used the hot fuel module did they? I hate that thing.
 
dyeager535 said:
I'm thinking the oil pressure switch is screwing up.

ECM is what controls the prime/relay, for it to keep running based on the relay, something would have to be wrong there, and it would SEEM unlikely for it to be an ECM issue.

Easy test, when it's doing it, pull the fuel relay connector and see if it stops. If it'd doesn't, it's the oil pressure switch.

These never used the hot fuel module did they? I hate that thing.
Click to expand...

Thanks for the ideas. Much cheaper than a fuel pump! Is that relay up on the firewall in the engine compartment? I'm thinking it's on the passenger side near the heater box. :dunno:
 
Alright, I pulled the fuel relay and the pump continues to run.

So, I guess its the oil pressure switch. BUT, if its the oil pressure switch, wouldn't the oil pressure gauge "not work" too? My gauge does work and moves up and down with the engine (as it should).

Still bad though?

Dealer wants $64
Rockauto wants $29
Dang!
 
Depends on year. Not sure what year they started using the combo switch/sender.

Three wires to the switch means it runs your gauge too. Two wires it's just a switch.

Off the top of my head I can't think of what else could have just happened other than the oil pressure switch failing, but disconnect it to make sure the pump does indeed stop.

I may get slapped here, as I can't find the post that I thought proved what I'm about to say, but I believe with either the relay OR the switch disconnected, the truck should start and continue running. Since your problem isn't consistent, I'd probably opt for that before replacing parts. It's easier than doing all the wire testing that you'd otherwise want to do. And with an intermittent problem, testing wires and components at any given time may be misleading.
 
But somewhere, someone had disconnected the oil pressure switch and started it too. I didn't cover that in the post you link to.

Theoretically various ECM's could be different and rely on the oil pressure switch instead of the relay/ECM to keep it running, but I doubt it.
 
Got it fixed, thanks for the help!

Sure enough, as soon as I unplugged the Oil Sending Sensor, the humming turned off! Also, thanks for the "pull the fuse" idea. Helped me drive the truck for at least a week until the parts came in.

Of course, it can't go flawlessly.....

Had to pull the cap and wires off. Also removed the coil. This was enough room to get in there pretty good. I also unplugged the distrubutor electrical connectors but didn't need to remove the distributor itself.

I was able to rotate the 90 degree fitting to allow access to remove the sensor. Once screwed on loosely, I then rotated back to the same location and then got a large socket on it for tightening. Plugged everything back together and all good!

So, the problems...... both the Oil sensor electrical connector and the distributor electrical connector both broke (locking tab snapped off). After a lot of searching, I actually found replacement connectors at Napa. Soldered everything together, shrink taped and I'm now good to go!

Good times!!

Oh, and mine was the 3 wire oil sensor as an FYI.
 
Glad you got it fixed! Too bad the sensor/switch was such a hassle to get to. Does your truck have the separate coil, or is it still in the cap? I would think the small cap setup would give you enough room to access?
 
dyeager535 said:
Glad you got it fixed! Too bad the sensor/switch was such a hassle to get to. Does your truck have the separate coil, or is it still in the cap? I would think the small cap setup would give you enough room to access?
Click to expand...

I have a separate coil mounted with two bolts just in front of the distributor.

I actually spent more on the electrical connectors than I did on the oil sensor. :haha: Oh well, a nice job to do.

I went to the junkyard on Sunday and found a factory roll bar for $25 so I grabbed it! :waytogo: It's for the older 74' era but in great shape......just couldn't pass it up. So overall, a great weekend!
 
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