Hi all!
I purchased a 96 blazer with 162000 on it for $600. It has a fuel problem. With the key on the pump would cycle but no pressure. Replaced filter and same problem. Pulled line off filter and turned key on and gas trickled out. I replaced the Airtek pump with a delphi pump. Tried to fire and it spit and sputtered. Well I shouldve drained the 2 year old gas. Dummy! pulld tank and drained gas. Reinstalled pump and changed plugs. Now I have zero pressure! Wth? Pulled return line off at pump and placed a catch pan unerneath it. Turned key on and off. The pump cycled for an excessive amount of time and dang near filled the shallow catch pan.
My question is would this indicate a faulty FPR?
Original owners records show one replaced 6 months before it quit running. Maybe an aftermarket cheapo like the fuel pump?

Thanks in advance.

 

This is a recirculating fuel system. Whenever the pump runs, the regulator sends unused fuel back to the tank. If the engine is not running, (and the pump is running) the regulator bypasses all fuel back to the tank.

When you initially turn the ignition to the RUN position, (engine off) the pump should run for ~ 2 seconds and shut off. If it continues to run, try disconnecting the oil pressure sending unit, (next to the distributor). The contacts in the OPSU may be shorted together activating the pump continuously when the ignition is in the RUN position.

There may be a problem with the electrical connector at the fuel pump module causing it not to work since replacement.

 

I will check the connections and keep you posted.

 

Another thing


If for some reason the regulator was stuck in bybass wouldn't that make it so it would not build pressure in the line? Could that also explain the long run time when the key is turned off?

 

If the valve plate in the regulator were to stick open, pressure at the service port would be extremely low, but there would be some. It would drop off to zero the instant the pump shut off. This would have no affect on pump run time. Extended run time is either sticky contacts in the fuel pump relay, or sticky/shorted contacts in the OPSU.

Check the connector at the fuel pump module. The old style connector was known for overheating and distorting the plastic, causing a poor, and eventually open circuit to the pump motor. Most new pumps come with the new style connector and it needs to be soldered to the vehicle harness, (do not use crimp connectors).

 

I installed the new connector when I replaced the pump. I also swapped fuel pump relay.
I let it sit for a couple days and it fired right up. Then ran for a minute and started boging down an died. Wouldn't restart. Tried it again today and it did the same. Also the fuel pump still ran for 45 seconda after key was off. Still need to check OPSU I guess. I am also going to pull off the upper intake and check the injectors it seems as if one or two is stuck open.

 

Unplug the OPSU, turn the key from OFF to RUN, (don't start the engine) and see if the pump comes on for ~2 seconds and then shuts off.

Also, checking fuel pressure and leakdown will tell if an injector or poppet valve is leaking.

 

The pump definetly sounds as though it primes when it comes on. But no pressure at the schrader valve. I am going to pull off the filter and check for pressur there.
So I guess with the OPSU unplugged it bypasses it so it should keep the pump runing when I crank the engine?

 

The OPSU provides an additional path for current to flow to the pump. It only provides the path when oil pressure is above ~7psi, (engine running). It is NOT any type of safety device. It can NOT prohibit the pump from activating, or shut it off if oil pressure drops below ~7psi. GM discontinued using the circuit on 1998 and newer 4.3L's.

The PCM activates the fuel pump relay for ~2 seconds, (called "fuel pump prime") when you initially turn the ignition to the RUN position. If the PCM does not receive a signal from the crankshaft position sensor during pump prime, it deactivates the relay. When you turn the ignition to the START position, the relay is activated continuously.

To check fuel pressure at the filter, it will require some "creative plumbing" with the pressure tester connection. All pressure and fuel flow must dead end at the tester. During pump prime, pressure must be 73psi to 108psi, and must remain above 55psi for at least 10 minutes after the pump shuts off. Post your results.

 

Ok so the reason I just lost pressure with the new pump was the pressure tester that worked a few days before must of came apart because the piece that pushes the needle on the schrader is missing all of a sudden.(bang head on wall!) I will find some plumbing to test this.