Engine problems

I have two XJ's
They both over the last mont have started acting up.
The 99 will start usually on the second try and runs fine then all of a sudden starts missing. If I rev it up the problem goes away and doesnt return until the next morning.
On my 96 I start it up it seems fine and then just dies. I restart it and its fine. Its like it is running out of fuel. and it doesnt do it every time.
I am thinking fuel pump does anyone have any ideas on this.
Thanks

Lardog

is the 99 throwing any codes? maybe a bad o2 sensor.

96 when was the last time you changed the fuel filter.

Both could be the IAC

Any check engine light on either of these XJs? If so, pull codes.

Some fuel pressure testing on both of your vehicles at the schrader valve on the fuel rail might not be a bad idea.

Try to get some data that leads you to the cause. Don't throw parts at it.

Neither XJ is throwing a code.
I will try the fuel filter since I doubt they have been changed over the last century. But I noticed the 99 doesnt have a filter in the fuel line but the 96 does. Whats up with that? Do they just rely on the filter on the pump?

Lardog

Sorry to threadjack, but when i went to de-pressurize my fuel system via the schrader valve nothing came, didn't seem like there was any pressure there...

my car had sat overnight when i went to test it, im wondering if that means my fuel injectors are leaking and not holding pressure anymore?

/threadjack

When the 1997 to 2001 Cherokee won’t start on the first try day after day, the first thing to suspect is a failed check valve on the fuel pump. The fuel pump check valve is supposed to hold pressure in the fuel line while the engine is off. The check valve is located on the fuel pump and located in the gas tank. A failed check valve allows the fuel to drain back to the tank. This results in the following symptoms:

SYMPTOMS

· Longer than normal cranking times
· Never starts on first try, almost always starts on the second try
· Rough idle for a few moments of idling
· Rough running for first ½ block of driving
· Little or no fuel pressure at the fuel rail test valve similar to this -

1- Key in on position; fuel pump primes for 2 seconds then stops. 0 PSI
2- Cranking over the engine. 2-3 PSI
3- Engine starts and idles for 20 seconds. < 5 PSI
4- Engine idles and fuel pressure creeps up to 45 PSI.


POSSIBLE CAUSES

· Failed check valve on the fuel pump in the gas tank (1995 ½ to 2001 models ONLY)
· Leaky fuel injector(s) may be the true cause of your problem, but more likely they are simply contributing to the check valve issue.

Testing of the fuel injectors should show if any are faulty and are allowing fuel to drain into the cylinder. Either problem can allow heat soak to vaporize the remaining fuel in the fuel rail and you may be dealing with a bit of vapor lock as well, especially in warmer weather.

1. Connect the gage at the fuel rail and start the engine. The gage should read 49 psi plus or minus 2 psi.

2. Turn the engine off and immediately clamp the fuel line just ahead of the fuel tank. Watch the pressure gage and see how long it takes to loose pressure.

If the pressure remains at 49 psi for an extended period of time then the problem is in the tank - probably the check valve. If the pressure falls below 49 psi fairly rapidly then the problem is probably a leaky injector.

There are a few solutions to the problem –

1. Turn the key to ON for 5 seconds and let the fuel pump prime. Turn the key to OFF, turn the key back to ON for 5 seconds, start the engine.

2. Crank the engine for 3-5 seconds, pause, and crank the engine again. It will almost always start on the second try.

3. Replace the fuel pump assembly in the gas tank. The check valve is not a separate part and cannot be serviced. This is both expensive and time consuming because you have to remove any hitches and skid plates and then remove the gas tank from the vehicle.

You can use solutions 1 or 2 for as long as you want to, they do not harm anything and the fuel pump will continue to function for many more years.

Thanks for a complete explanation I will try this process and see where I get.
Lardog