Hey guys, so recently i sold my 91 and went out and bought a 98 Cherokee 4.0 classic and when i bought it i just drove it home and parked it since it wasn't registered or anything yet. After a week i started to drive it more often and some times it just cranks instead of starting up. when it starts up there is almost no delay time, just starts right up, but other times it will just crank and never start and when that happens i just stop try it again and fires right up....kinda weird right

only other issue is the oil pressure sometimes is really now but my dad said he will check that out because he has a tool to hook up and where the sender unit goes to see if its the unit or the actual oil pump....also told my dad about this issues and he said it might be the fuel pump? any inputs? thanks

 

On mine if I turn the key on I hear my fuel pump run a sec or two. Then key off then on again and the pump will run again. The third time it stops quick then will fire right up. Probably I have a bad check valve in my pump, but the pressure could be leaking somewhere else.

 

1. The extended cranking time is most likely the check valve on the fuel pump assembly starting to fail. It is a VERY common failure on the 98 XJ. More on that below.

2. Your dad is smart. Hooking up a mechanical gauge temporarily where the oil pressure sending unit resides is the best strategy for any low oil pressure readings. Good data = good decisions. I've included the oil pressure spec for the 4.0 below

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

 

thanks! ima take it to my dads shop sunday and hopefully start putting on the lift kit and check some of the problems monday, really appreciate your help