Problematic 99 XJ

[mheinsohn1]

I bought this Sport/Classic from a dude on Craigslist stating it wouldn't start and was a project. Took my buddy, outstanding mechanic, went through it and did a compression check and paid 2k pushed it on the trailer and took it home. Got it back to the house and my buddy discovered it was 180 degrees out of time with extremely loose battery cables, up in running in under an hour. The gauge cluster was intermittent, pulled it out added dialectic grease and works flawlessly now. Leaks like a P/Q, but I monitor and keep topping it off with fluids.

Drove it for a bit and was getting 7-9mpg, googled my a** off and eventually replaced the exhaust manifold, now getting 14-17mpg Runs relatively well for 196K miles. It began having some serious overheating problems and discovered it the electric fan wasn't kicking on, so now I never get into traffic, I know "not a safe precautionary measure" but until last week I couldn't really afford to buy the parts. The heater also doesn't get hot.

Sporadically started to run a lean code, it would throw the code for a day or so then go away, I was driving maybe 30-60 miles a day during this. Took it to my Uncle's shop and he ran the computer on it, block/head gasket test and fuel pressure. He said all the numbers were coming back good o2 sensors were sending the right numbers, no negative results from the head/block test, fuel pressure was perfect and couldn't find anything that would identify a lean reading. His advise was order and install new fan shroud, electric fan and heater core and go from there. So ordered now, should be here in a week.

Recently it started giving me issues starting, turns over with minimal effort just doesn't catch sometimes, catches eventually after a few seconds (3 typically, worst was 10). Again, Google-Master, I would put it in neutral and see if there is any difference, none. Neither my buddy nor my uncle are Jeep gurus, so I figured I'd reach out to some SME's in the field and hope for some good-valid ideas or even better, answers.

Any and all help/advice is greatly appreciated, thanks in advance.

6Cyl 4.0 (196k) / Automatic / NP242 / Chrysler 8.25 / Has a Zone suspension lift, maybe a 2" on 31's

 

[Tim_MN]

When a 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 one or more of 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 45-50 PSI.


POSSIBLE CAUSES

• Failed check valve on the fuel pump in the gas tank.
• 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 gauge at the fuel rail and start the engine. The gage should read 49 psi plus or minus 5 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 one or more leaky injectors.

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.


If you do replace the fuel pump assembly, purchase a high quality OEM style pump assembly such as Bosch or Carter. Some cheap aftermarket fuel pump assemblies, like Airtex, and Precision don’t hold up and fail completely within 12-18 months.

 

[mheinsohn1]

Thanks for the indepth response, so would this last tidbit (completely forgot) help the cause of fuel pump? The fuel gauge is intermittent also?

 

[Tim_MN]

The fuel pump can work, and the gauge not, or the other way around.

 

[Gator Bait]

On my 99 I was getting a lean code. The mechanic told me my new Bosch O2 was good according to his scanner and had me replacing other parts. Ended up getting an oem O2 sensor and all was well again. These things hate aftermarket sensors.