Fuel pickup problem?

[badgto]

Have a 94 GMC with 4.3, fuel pump quit and replace it and fuel pump relay. Works fine, as long as its warm, seemingly if it is not at least 45 or above it won't start. Still firing and everything, just don't hear pump run. Could it be something with the pressure regulator? Any help will be appreciated!!!

[ChevyTech]

I am assuming this is a TBI 4.3 in a full size truck

If the fuel pressure regulator spring breaks the pressure will be low because the fuel is being dumped in the tank rather being held under pressure in TBI unit, and the pump should still run.

The ECM controls the fuel pump relay.

The truck has a fuel pump relay that supplies power to the fuel pump when:
- Anytime the ECM receives a distributor reference pulse. (Engine running / engine cranking)
- The key is turned on engine not cranking – relay applied for 2 to 20 seconds (most trucks 2 seconds), depending on emissions equipment. Trucks over 8500 GVW and some other vehicles have and electronic Fuel timer module that allows the pump to run up to 20 seconds.
The key must be turned off for a certain amount of time before it will prime the system again when turned back on.

The truck may have a failed coolant temp sensor for the computer. The computer uses the coolant temp to determine how much fuel to inject and how fast the idle speed should be.

It is common for these sensors to fail. Usually when they fail they make the mixture go to rich.

[badgto]

Thanks Chevy Tech, yes it is a full size, 1/2 ton. So maybe try coolant sensor first, since after the morning temp warms up trk starts fine? Just like this morning once the temp was up somewhat it started right up. But when I first went out to try at about 6:30, nothing.Thanks again!

[ChevyTech]

You’re welcome!

If the coolant sensor does not make any difference, try to notice if it seems like it is not getting enough gas, or if it seems like it is getting to much gas.

So how do you get it started when it is cold and will not start?

[badgto]

Don't, just let it set till it warms up. Have chked tb when cold, took breather lid off and it has no gas coming out of injectors. But as I stated once it get say, 10 or so in morning, or roughly around at least 45 degrees, you turn key and you can hear pump run, and presto it starts right up.

[ChevyTech]

If you are sure it is an issue where the fuel pump only runs when it is warmer, then don’t bother with the coolant sensor.

When you turn the key on the fuel pump should run at least two seconds. If it won’t run, the fuel pump, relay, wiring or the computer have a problem.

I don’t think the problem is the computer. My guess would be it is the fuel pump or the connections to the fuel pump.

I suggest only using OEM (Original equipment manufacturer) fuel pumps.
I have seen so many aftermarket fuel pumps fail during their warranty, or just after the warranty expires, that I strongly suggest you stay away from aftermarket pumps.

Often when a fuel pump won’t run, if the bottom of the gas tank is hit with a rubber mallet, just as the key is turned on, the pump will run. My guess is that new pump does not want to start spinning when it is cold.

[Weasel Diesel]

Originally Posted by ChevyTech

I suggest only using OEM (Original equipment manufacturer) fuel pumps.
I have seen so many aftermarket fuel pumps fail during their warranty, or just after the warranty expires, that I strongly suggest you stay away from aftermarket pumps.

AMEN Brother !!!!!!!