Carbed 92 with fuel issues

[Needs15]

So I'm helping a buddy out with his truck he recently bought. When he bought it, it ran and everything seemed fine. A couple days later after he got it home he went to start it and it wouldn't start, they tried a couple things and decided they thought it was the pump so they changed the pump out. Still couldn't get it running. So they asked me to come help out and see if I could come up with anything. I found that the relay for fuel pump wasn't working so changed that and now the pump engages for the 2 seconds when you turn key on and the truck will fire but won't stay running. So cycled the key a few times to get more fuel up to carb and got it to run longer and seen there was no pressure at the gauge that was installed at the carb. So my question for you guys is, it seems like after the truck is running the fuel pump stops working why would this be? Could it be an ignition thing that's not sending power back to pump after its running or a computer issue? We did get it running one time after for a good 5 minutes and had fuel pressure of about 1.5 to 2 psi and it ran good you could Rev it up and everything seemed fine and then next day it wouldn't start again and stay running and no fuel pressure. I'm baffled at this one.

 

[PlayingWithTBI]

Do you still have the oil pressure switch on the back of the engine? It almost sounds like it, or the connection, is intermittently wigging out. Here's a picture of the switch (circled in red) on top of the china rail.

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[Needs15]

Yes it's still there and connected, oil pressure gauge and sender works fine as far as I know, it comes up as the engine turns over and when we had it running for the 5 minutes it was fluctuating as we were revving it up as per normal, I have tried wiggling every connection for fuel pump wires and they are all tight from what I can tell, I don't see any visible breaks or kinked wires aside from taking out the whole harness and checking but the fuel pump engages everything you turn key on

 

[LC2NLS6]

How is the relay wired? I used the pink wire from the factory coil as a trigger since that is also hot while cranking (I need that for Holley EFI). Check grounds and verify 12+v at the pump. Buy a volt meter and use it. Clogged filter? Bad regulator?

 

[PlayingWithTBI]

Yes it's still there and connected, oil pressure gauge works fine as far as I know, it comes up as the engine turns over and when we had it running for the 5 minutes it was fluctuating as we were revving it up as per normal

This switch has nothing to do with the gauge. It turns on the fuel pump when it sees a certain amount of pressure, which bypasses the fuel pump relay.

Another thing, when the ECM sees 400+ RPM it turns on the fuel pump and fires the injectors so, you may have 2 different issues.

 

[Needs15]

It's the stock relay, all wiring is stock that I can see. They installed a new filter when they did the pump a couple days ago. If it's a bad regulator would it prevent fuel from coming up after its running? It gets fuel to the carb with just that 2 second prime when key is turned on.

 

[Needs15]

I have a tbi motor that I'll pull oil sender and put in and see if that works.

 

[Needs15]

Thanks for the help PlayingWithTBI Sender was bad so got that changed and it works like it's suppose now and actually runs. Regulator might be bad as well as it seems like it's getting too much fuel even though gauge only shows 2 psi. My buddy can now deal with the rest and have somebody tune it up and get it running better as thats not my forte

 

[PlayingWithTBI]

Thanks for the help PlayingWithTBI Sender was bad so got that changed and it works like it's suppose now and actually runs.

Glad you got it running but, that switch is more of a backup than a primary path to the fuel pump. You may want to look more into the way @LC2NLS6 did with his. I'm just saying this is the way it s/b when running a stock setup.

 

[Schurkey]

Another thing, when the ECM sees 400+ RPM it turns on the fuel pump and fires the injectors so, you may have 2 different issues.

Since this is a carb-swap nightmare, it's probably also a distributor-swap debacle, too.

If they swapped dizzys, the computer is probably sucking air for sensor information, such as RPM. No RPM signal...no fuel pump engagement except for prime and after that it's the oil pressure switch bypassing the relay.

That makes the oil pressure switch double-critical, and apparently whoever carb-swapped this mess didn't compensate by re-wiring the fuel pump relay. So now that falls to the new owner.

I wonder what other "surprises" the carb-swapper left for the new owner.