98_XJ Sport

1998 Cherokee XJ Sport is having some trouble starting after a few hours of sitting. Battery is great. Any suggestions on what to check next?

tjwalker

More details needed.

Do you mean that it turns over fine but doesn't actually "start" or that it doesn't turn over well? Or does it turn over fine but takes an "extended crank" time to start.

If it isn't turning over well, job #1 is to clean battery cables and battery posts until they are shiny. There can be a corrosion film which creates resistance.

And the only accurate way to determine battery condition is to have it "load tested", which any parts store will do for free.

If all of above check out, get a meter. With the key in the ON position, measure voltage directly at the starter. It should be approximately the same as what the battery itself measures.

If you have good voltage at the starter, then the starter itself is suspect. If you do not have good voltage, then you need to start working your way back to figure out why (bad cable, bad engine ground, etc).

And yet another starting type of problem is this. If you have to crank the engine for a long time to get it to start (cold engine), the problem is most likely a failed check valve in the fuel pump assembly. Very common failure. The check valve is in the fuel pressure regulator part of the assembly and when it fails, it causes the fuel pressure to drop dramatically, requiring lots of cranking to build it up to a point where the engine will start...........

98_XJ Sport

It takes "excessive crank time" and it only happens when it has been sitting for more than 2 or 3 hours. If I start it, shut it off and try again in 5 minutes or even an hour it starts up just fine.Cleaning off the posts and cables was the first thing I did and helped very little. I've gone to AutoZone and they ran a check on the battery. I'm thinking he didn't check anything else but said my alternator might not be charging my battery all the way or the aftermarket stereo deck that was installed when I bought it could have been installed incorrectly and has an open circut, I've since been removing the faceplate and it has helped some, but the problem still exists. I ran my own volt test on my battery last night and found nothing that needed attention. Today I plan to volt test my alternator and take a look at my starter.

tjwalker

The check valve in the fuel pump assembly is most likely your problem. It is so common that I have the below information in a "cut and paste" format, ready to copy. Try the "poor mans prime" described in the information below to help you troubleshoot this. Takes only a few seconds before your next cold start.
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The check valve is located on top of the gas tank and is part of the fuel pump assembly on 95.5-2001 vintage 4.0 XJs. When the check valve starts to fail, it reduces fuel pressure to a point where an extended crank is needed to start the engine. It is a very common failure. I experienced it on my 99 at around 75K.

A good (and simple) way to troubleshoot this problem is called “the poor mans prime”

1. Turn key to ON position (do not crank the engine!)
2. The fuel pump will energize and run for a couple of seconds
3. Turn key to OFF position
4. Repeat above a two more times
5. NOW crank the engine over

If the engine starts quickly and cleanly after performing this procedure, you may have the check valve issue. If it starts and runs poorly for a few seconds, it could also be a leaky fuel injector resulting in the bleed down and the stumble upon startup is the engine clearing the excess fuel that has leaked into the cylinder because of the faulty injector.

Also be aware that a bad battery can give you this symptom. Sounds strange but it definitely does happen. Have battery load tested if you have any questions; your XJ does NOT like low available battery voltage. Be sure battery connections and posts are CLEAN.

Some troubleshooting tips for extended crank times:

Hook up fuel pressure gauge on the schrader valve on the fuel rail

Start engine and bring to normal operating temperature.

Observe test gauge. Normal operating pressure should be 49.2 psi (plus or minus 5 psi)

Shut engine off.

Pressure should not fall below 30 psi for five minutes.

If pressure falls below 30 psi, it must be determined if a fuel injector, the check valve within the
fuel pump module, or a fuel tube/line is leaking. An adaptor tool/hose included with the fuel pressure gauge can help you with this. Consult gauge manual for more information on this but here is basically how it works:

*Turn the engine off and immediately clamp the fuel line at the adaptor hose. Watch the pressure gauge and see how long it takes to lose pressure.

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

You can limp a check valve problem along indefinitely if you wish as it doesn't mean the fuel pump itself is going bad. Normally, the check valve is replaced as an entire assembly as you have to drop the gas tank to access the assembly. Fuel pump assembly consists of fuel pump, regulator, check valve, filter. If you do replace the fuel pump assembly, purchase a high quality OEM style unit. Some cheap aftermarket assemblies don’t hold up and fail prematurely. I specifically seek out Bosch fuel pumps as they are the best in the business. Stay away from Airtex, as IMHO, they have a bigtime reliability problem.

98_XJ Sport

Sorta off the original topic but this is my first Jeep so I have lots of questions... is it normal for my oil pressure to go down to almost 0 on the gauge when idling and return to normal 40 when driving or do I have a problem?

bigboy813

You may want to check your oil... if not its either your gauge or your oil pressure switch

tjwalker

The spec for oil pressure for the Jeep 4.0 is as follows:

*Not less than 13 psi at HOT idle
*Between 37-75 psi over 1600 rpms

So the answer, is no.....your oil pressure reading should not go down to zero.

Low oil pressure readings should ALWAYS be confirmed. Best way to do that is with a mechanical oil pressure sending unit. They can be rented from many parts stores; call around. Temporarily install it where the oil pressure sending unit resides. Then you'll know for sure. Good data = Good decisions

It could be the sending unit (best case and easiest repair), it could be the gauge, or it could be real, but if it was real you would usually hear a knock in the engine if the pressure truly was running near zero.

Confirm it.