MudFlap

With fuel pressure gauge hooked up, I can turn on switch, fuel pressure only gets up to about 3-4psi, and pump only runs for about a second. I can jumper across fuel pump relay and it goes right to 40-42. If I crank on it long enough to start, fuel pressure goes right to 40-42. As soon as I shut switch off, fuel pressure drops to zero. The fuel pump was just replaced a coupla weeks ago. Worked great for a few days. Any ideas? Thanks in advance! This is on a 95 ZJ with 318.

MudFlap

No one? Man, y'all are a tough crowd

Digitalsam

I am still waiting on a response to my recent post, and because you have a nice 1911 signature, I will try my hand at this.

The fact that you can start it, I would think, would indicate that the pressure is not 3-4 psi, but maybe the gauge is goofed. Could it be something electrical that would cause the gauge not to register unless you have full power to it. The fact that you are able to get a good reading by jumping the gauge seems also to point to a short or weak connection. I would try to trace the wiring back.

I am not a mechanic, nor do I play one on TV. Take it for what it's worth. Hope it is helpful.

Programbo

If you don't do anything and try to start it what happens? It eventually starts and runs bad or just takes a long time to start? You say "hard to start" which makes me think it does start and run eventually?

MudFlap

It's a direct read mechanical gauge that connects to the port on the fuel rail, not an electrical gauge connected to the electrical system in any way......

Good thinking tho...

And yes, I have a bit of a love affair with a 1911. I will never disgrace myself with owning one in 9mm - our defeated enemy's inferior caliber. All mine are .45, because shooting twice is just silly, and 9mm is for those who squat to pee!

Yes, it'll eventually start after some cranking. I can watch the fuel pressure rise as it cranks. When pressure reaches about 40 psi, it'll bust right off. Given that it's an electric pump, not mechanical, it makes me wonder about possibly a crank position sensor. Any way to test it with multimeter?

Programbo

Hmmm..A long crank to start is a lot of times a symptom of a fuel injector that is "leaking down" or stuck open a bit.

MudFlap

Hmmm, I hadn't put much thought into that.

ET JEEP

The crank position sensor has to do with ignition. It does not play a part in the fuel system.

When you turn the key on the fuel pump should run for a few seconds to prime the fuel rail. It then shuts off waiting for engine start. The fact that it takes a long time to crank means you do not have good fuel pressure. It slowly builds until you get enough to start. You appear to be losing fuel pressure somewhere.

What happens when you shut the engine down, wait a few seconds and do a restart? Does it start easily or does it labor again for a restart? Not sure how much pressure the system should hold with engine off. You do have a check valve to hold fuel pressure when you shutdown. Troubleshooting the fuel pressure problem is where I would look.

MudFlap

As soon as I shut the ignition off, running or not, fuel pressure drops off to nothing. Where is this check valve? Is it part of the fuel pump like the regulator is?

Programbo

You might want to check if you have an injector stuck open. The only way to really do that (Without having a test bench) is to get the fuel system up to pressure (But not let the exhaust get to hot in case you leak some fuel on it) and pull the fuel rail off (But with the engine OFF. Do not pull the rail with the engine running) but leave everything attached. Injectors, fuel line etc. If you have one stuck open or partly open you will see it still dripping or spraying a bit.

If that seems fine then you will need to work backwards down the line from there.

Bustedback

Pull the dipstick and give it a sniff, if you have an injector leaking after you shut the engine off you will smell fuel in the oil and the oil level will be higher to some extent. My money is on a bad pump causing your problem.

dave1123

I believe the fuel pressure regulator is in the filter. It probably is leaking pressure back to tank. The pump will overcome the leak if it runs long enough, resulting in a start. On your 95, the filter is outside the tank. If it has 3 lines, the regulator is in the filter.

On the 1911, It saves ammunition because it will drop a man on the first shot. Even with body armour, it will at least knock him down. .45 APC is fine, .44 Mag is overkill.

Just a thought. If you had a leaking injector, it would still start on the rest of them! I still think your problem is fuel supply pressure.