Hi again, my second thread of the day.
2000 Jimmy, 4.3l, 4x4.

A very frustrating problem that apparently many have with the Jimmy. Lack of fuel pressure, but it's about impossible to find the problem. Maybe you guys can point us down the right direction.

A few months ago the fuelpump went. No problem we swapped it out and everything was fine. Shortly after it started giving us a headache with the initial starting when the engine was cold, the engine would crank over but it wouldn't fire up, after trying a few times it would start and run just fine for the rest of the day, would also start fine as long as the engine would be started again soon.

Battery died on us, put in a new battery. Probably coincidence that it went at the same time as the other problem. New battery did not make any change with the starting problem.

Took the fuel pressure at the test port in the engine compartment, attach the gauge, relief the pressure through the gauge, turn on the ignition, not starting the motor. Yes I can hear the pump running the initial few seconds when turning the key. Pressure went to about 50-52psi. Ok, that's not enough to start it.
Change the fuel pressure regulator.But the pressure wasn't really any higher.

Change the fuelfilter. Tried to get all the air out of the lines by attaching the pressure gauge on the test port in the engine compartment and relieving the pressure a couple times, with the ignition on and off etc. Pressure did come up, truck started, I thought we fixed it.

This morning it wouldn't start again. We looked for a fuel leak everywhere, can't find any. There is no smell of leaking fuel either. Sparkplugs have been changed. There is fuel in the tank!!! And when it runs, it runs fine without problem.

Tried to switch the module for the fuelpump with a different module, (Horn) just to see if it make a difference, nope.

It has to be something electrical, but where do I start the testing?
Where and what needs to be tested and how many Volt does it have to have where? How can I test the Voltage going to the pump without being able to unplug the connectors on the pump itself and see how much power actually goes to the pump? (Not enough space to reach in and unplug the connectors from the pump)

One strange thing....the battery is fully charged, 12V, but if we hook up a battery charger for a bit.........the truck will start. If I take the charger off....the truck will turn over great but not start.

Help, is all I can say!!!
Please and thank you.

 

whats the pressure turning the key on ?

 

 

Fuel pressure at the fuel line valve is at 50psi with the key turned on and holds steady. Didn't try to start it.
Fuel pressure goes up to 58psi if I hook the charger on to the battery, key turned on, I have to stress though again, the battery is fully charged and showing 12.59V at the battery terminals.

 

Long day working on a bobcat i didnt read right lol

if the pressures 52 psi with the key on its sorta low

 

Fuel regulator dumping pressure into the return line.

 

The fuel pressure regulator has been changed 2 days ago and did not bring any change in fuel pressure.

 

Hook up tester check it and then hit release button, if it goes up and starts up then you are getting air in to the system, start at tank check connections

 

If he has air in the system it would have to be coming from before the pump on the suction side. After the pump it will be under pressure and will show up as a fuel leak. However after shutdown it could turn into an air syphon, however if the pressure isn't bleeding down past spec (check the tech articles for diagnosis) then likely there isn't a leak between the tank and the schrader valve.

 

Tobashadow: I'm a bit confused there. You want me to hook up the fuel pressure gauge, turn the key on, leave the key on and release the pressure? You are saying that if the pressure goes up I have an air leak somewhere.

What about the power supply though. If I hook up a charger to the already fully charged battery I end up getting a higher pressure, like 58psi. How can that happen despite the possibility of an air leak?

By the way, I grounded the pump directly to the frame too to guarantee a good ground.