dkroll

2001 Cherokee, 4.0L. ; I am at wits end- She runs just fine and performs great all the time. The issue; More often than not she will not fire right off on the first crank. Sometimes it will start quickly but most of the time it doesn't want to start on the first attempt. On the first attempt I can just hold the key in start, it will crank forever (like for up to 30 seconds) then start but run like crap and possible throw misfire codes and after rev-ing it up for about 10 seconds then it will stabilize and run smooth from there on out. It has done this for over a year now. When I go to start it, people around me start counting on their fingers, most the time "two" fingers, a smile and scratch on the head just about 95 percent of the time. Temp doesn't matter. Starter cranks fine. I sometimes "fake" it out by hitting the starter for only a second then go straight to the second crank when in a rush. Where do I start for testing? Coil pack were replaced, plugs also. Side note- when it isn't a smooth idle start, I can smell a smell like 5 year old gas for a few seconds- then down the road I go and runs great. Help, I am going crazy!

tjwalker

This is likely a "fuel" related issue. Quite common actually on the XJ. So common that I have written up a cut and paste answer for you. First thing for you to try is what I describe as the "poor mans prime", shown below. That one simple test goes a long way in telling you if you have a leakdown of fuel pressure. Most often it's the check valve in the fuel pump assembly, but it is not impossible that you could have a leaky fuel injector too. Anyways, enjoy the read, welcome to the forum and keep us posted!
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The check valves (there are two of them; the primary one is on the fuel pressure regulator and a secondary one can be found on the fuel pump itself) are part of the fuel pump assembly on 95.5-2001 vintage 4.0 XJs. When a check valve starts to fail, it can reduce fuel pressure to a point where an extended cranking time 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) first step in helping you 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 about 2 seconds. Be sure to wait until it stops running.
3. Turn key to OFF position
4. Repeat above steps 1-3 two more times
5. NOW crank the engine over

If the engine starts quickly and cleanly after performing this procedure, you may have a check valve issue. If it starts and runs poorly for a few seconds, it could also be a leaky fuel injector resulting in the fuel pressure leaking down and the subsequent 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 starting symptoms as well. Have your battery load tested (any parts store will do this for free) if you have any doubt; your XJ does NOT like low available battery voltage. Be sure battery connections and posts are CLEAN.

Some troubleshooting tips for extended crank times. You will need a fuel pressure gauge. Many parts stores will rent you this tool inexpensively.

*Hook up fuel pressure gauge on the schrader valve on the fuel rail under the hood

*Start engine and bring to normal operating temperature.

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

*Shut engine off.

*Observe pressure on gauge. Pressure should not fall below 30 psi for five minutes.

If pressure falls below 30 psi, it must be determined if a fuel injector, a check valve within the

fuel pump assembly, or a fuel tube/line is leaking. An adaptor tool/hose normally included with the fuel pressure gauge can help you with this. Consult the manual that comes with the fuel pressure gauge and the Factory Service Manual for your year XJ for more information on this exact procedure, 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 – most likely a check valve. If the pressure falls below 49 psi fairly rapidly then the problem is probably a leaky fuel injector.

**Note. Where check valve is suspect, a quick loss of fuel pressure is often the fuel pressure regulator check valve and a slow loss of pressure is often the fuel pump check valve. But keep in mind that either or both check valves can be to blame.

You can limp a check valve problem along indefinitely if you like, as it doesn't mean the fuel pump itself is going to fail. Perform the “poor mans prime” before cranking to speed up your starts. However, if you have a check valve issue and want to resolve it, it is recommended that you replace the entire fuel pump assembly for two reasons. First, you have to drop the gas tank to access the assembly. Secondly, with two check valves, replacing just the fuel pressure regulator where one of the check valve resides may or may not resolve your problem; remember there are two check valves; the other check valve is part of the fuel pump.

The fuel pump assembly consists of fuel pump, fuel pressure regulator, fuel gauge sending unit, fuel gauge float, pickup filter and pigtail wiring harness. If you do replace the fuel pump assembly, purchase a high quality assembly. Know this….you do get what you pay for here. Some cheap aftermarket assemblies have been known to fail prematurely. I personally prefer Bosch fuel pumps as they manufacture the best fuel pump assemblies for the XJ. Carter is my second choice. Airtex is my least favorite choice and I will not recommend or install them. A Google search will show you why.

dkroll

P.S. 182K miles. Could it be a CAT issue? Or could it be a stretched timing chain causing a delay in the ECU responding?

dkroll

Thank you, I will do exactly what you mention. I will post results as I go along.

dkroll

Solved (so far)... I have tried the "poor man's prime" several times and that didn't work for mine but good troubleshooting knowledge. I threw in a new fuel pump assy yesterday and so far (5 out of 5) times it has started right up on first crank! Yippee!!! Even this morning after sitting all night. It seems to be running better and more power up hills. I noticed the little filter on the bottom of the old one had fallen off also. Thank You!
P.S. I want to take the old one apart and see the checkvalve. I hope I can find it.

Now I can get back to my project 1988 Comanche.

tjwalker

Thanks for the nod; glad I could help! And for checking back in with what you found. Not everybody does. We're all learning here. One thread at a time.

Good luck with your Comanche! I had an 88 Comanche and it was trouble free until the day I sold it.

dkroll

Yes, I love when people give "closure" to issues, otherwise I surf and surf for just that. I am doing a "half frame" up on the 88, new floorboards and crazy long arm lift, I am one to go extreme measures and in it ten years on and off. ALL is being cleaned, painted, replaced with new. Eventually it will be brand new. Hobby and don't like payments on this new line of cars! Thank you again!

dkroll

I was wrong..............( I hang my head in shame)...........
The new fuel pump assy worked great, then yesterday, I heard a weird "pop" noise or something and now I am back to the same old issues. It was nice for a bit, but my regrets are (I think), I will be back under my Cherokee to replace the unit again BECAUSE....I am a cheap guy and thought I would get a great deal on ebay just to take care of my troubles. I have read a ton of stuff since my new troubles, and Cheap is probably not the best at all. I NEED BOSCH EVERYTHING!!!!
Here is the problem, I tossed my old stuff.........
I see just the pump, and stuff.....but not the complete setup.....
HELP!!! I AM GOING CRAZY JUST TRYING TO DO THE RIGHT THING NOW!!!!!!!!

gat

What is the pressure in the rail? Do you hear the pump priming when you turn the key to on? Have you measured the voltage going to the connector of the pump? A weird pop makes me think that your wires could have worn and shorted. Check for discontinuity between each wire in the connector as well as voltage and ground.

dkroll

My pressure is good and pump is working fine, I bought a cheap replacement pump assy and the check valve blew I am sure. The fuel runs back to the tank when key is off because of this. The crank time before starting is my issue. Pump goes on so not thinking electrical problem. I hear the BOSCH unit is the way to go because the cheaper ones dont last (check valve) And I dont want to drop the tank again after this. I have seen electrical issues with my older Cherokees in the past though. Thanks for the info.