rember

Hello you all, first post here.
Ok, will try to be as clear as possible on my situation.
When the truck is cold like in the morning. (considering it does no get to cold here where i live.) I can't get her going, sometimes she will feel sorry for me and it starts, but not right away.
I have notice that, when she dosent start, the fuel pump stays on with buzzing sound, and the battery gauge and gas, stays dead.
Sometimes when the fuel pump stops the buzzing sound, i see the gauges work as normal, and starts, but sometimes it wont.
I have replace the cks, is driving me crazy, everything else seems to be working fine, i have spark and fuel pressure just fine.
Any help will be greatly appreciated
Thank you

tony270

It sounds like the fuel pump is going kaput, my thought is that the pump is internally shorting drawing the voltage from gauges, the when the fuel system becomes pressurized the fuel pump stops and the gauges start working again, or the fuel pump is leaking internally causing it to overwork past it's duty cycle causing the same kind of draw. With that it is normally just a matter of time before it totally fails. If that is the case, you were very observant and notice the warning, so when is goes kaput, you'll know where to start looking.

tony270

The sound that you described seems like the fuel pump is pumping to pressurize the fuel injection system, when the predetermined psi is reached the pump should stop. If it (the regulator) doesn't detect the predetermined psi the pump will overheat. I never overlook the obvious like clogged or restricted fuel filter or line/s, or a leak, and I never let my fuel tank get below 1/4 tank, keep a good fuel cap tightly closed.

dave1123

The fuel pump runs continuously as long as the engine runs and the pressure is controlled by a pressure regulator, on the 5.2, it's on the side of the throttle body and the 4.0 is in the filter or on top of the tank. When you start it, the pump runs for a couple of seconds just to charge the system with fuel in case it leaked down. It's not pressure controlled, but a timed cycle.

You might have a fuel pump relay about to fail.

tony270

To clear any confusion the fuel relay on my 95 ZJ 5.2 is in the fuse box behind the battery in the engine compartment. And the fuel pressure regulator is in the fuel tank incorporated/attached to the fuel pump. I think the sound is coming from the fuel tank when the key is turned to the the run position without the engine running, correct?

rember

Thank you all for the quick responses.
Reason i ruled out the fuel pump is because i have a good fuel pressure on the rails.
Yes the sound is coming from inside the tank.
I did check the relays, and they seem ok,
One other thing i forgot to mention, is that the security alarm light on the dash stays solid on, even though, the security system has been apparently disable.But sometimes, very rarely, the sound stops, and the the alarm light turns off. Weird huh?
I'm very confuse, as i was under the impression, that, if i have good fuel pressure, its not the pump, im stump....

rember

Tony270, where is that regulator you mention? that could be something to look into it
thanks

rember

Thank you Dave, i see you already point it out where this regulator is.
Will test the relays, they seem ok, but will have a closer look.

dave1123

Oh, it's not the pump, but power TO it. That comes from the fuel pump relay which is controlled by the PCM. It sounds to me like the alarm light is now an indication of the control system functioning. Something is telling the PCM it shut down the engine. When you replaced the crank sensor, did you inspect the wire harness for frayed insulation or loose connector pins?

Actually, the gauges not working suggests the interruption of power to the PCM, but why is the fuel pump energized when that happens? You're right! It's confusing.

I just had a brain fart! It MAY be possible the fuel tank gauge sensor is shorting to the fuel pump supply wire, causing the fuel pump to run and pulling power from the gauges. Check the harness at the tank.

rember

Yes i did, all the wiring connected to the camshaft sensor look fine.
I'm thinking of dropping the fuel tank today and hoping to find something there, if i do not find anything odd, my next step will be to run and run and never come back to a civilized world.

tony270

This is a very common fuel pump failure symptom, on the 95 ZJ 5.2 the fuel pump is inside the fuel tank and the fuel pressure regulator is in the tank with it.

rember

Thanks Tony.
one question, is '95 and '96 similar? does the '96 also has the regulator inside the tank, got a bit confused there, where the regulator is exactly as other someone else mentioned that it is by the throttle housing.

tony270

Yes it is in the same location, in the fuel tank. On many vehicles of this vintage the fuel pressure regulator is located inline just before the fuel injection rail, on throttle body fuel injection it is different. You don't have throttle body fuel injection, that system is utilized on the older/previous generation vehicles.

rember

Gotya
dropping the tank as type will see how that goes.
how do you recommend to test the Regulator and what readings should it have?

tony270

The fuel pump and regulator come as an assembly. So if the pump is kaput or the regulator the assembly should be replaced as one, that's how I do it. I also make sure to install a new filter sock or equivalent, and I replaced the fuel filter and fuel cap. I think the assembly cost from $100.00 to $300.00.