01cherokeeguy

I have got a 2001 Cherokee with about 159k on it. Purchased it a few months back for a good deal, although I knew it needed a few minor things.

Since I got it, it had somewhat of a starting issue. It would sometimes start the first try, but usually not and then it would fire right up on the second try.

Soon though, the check engine light came on with the code P1494 (Leak detection pump pressure switch or mechanical fault.) It would also run roughly for the first 10 seconds or so that it was started unless I gave it gas.

It ran and still runs well after it starts and the fuel starts pumping. I diagnosed my situation but doing the "poor man's prime." I would turn it to on position, then off and repeat 2 times. As long as I do this it will start up good every time, although if the engine isn't warm it will have the rough start.

This all started about a month ago. I recently realized that when idling it would shake occasionally but not too bad. Then yesterday, I got out of work and went to start it. It did the rough start and was really cold outside (I live in Minnesota) and on start up, the check engine light started flashing. I know this is bad, but I let it warm up for a minute and everything ran fine. I got home fine and nothing seemed different.

I woke up this morning and went to start it, doing the poor man's prime first, and there was no flashing check engine light so I figured I was fine. I ran some errands, no problems. I brought it to the local auto parts store to see if I had any new codes and the only one that popped up was P0301 (Cylinder 1 misfire.)

So do you guys have any ideas as to what exactly could be happening? Should I be driving it right now or is it bad to drive on 5 cylinders? Any information or advice would be fantastic, as I love this jeep and I don't want anything to get worse.

Thanks in advance

Turbo X_J

What have you performed in the way of maintenance? With any used vehicle it's entirely fair to assume the previous owner(s) only filled it with gas and had the oil changed if/when they remembered.

tjwalker

For a single cylinder misfire on a 2001 XJ, the first thing to try is new spark plugs. I recommend NGK copper plugs for the 00-01 XJ. Be sure they are gapped to .035 before installing.

As for the extended cranking time before starting, the most likely root cause is a failing check valve in the fuel pump assembly. More on that below. You can either live with it and keep performing the "poor mans prime" or chase it.

Enjoy your XJ and one piece of advice for you to keep in mind. Keep a close eye on the coolant reservoir under the hood. Some (not all) of the 00-01 XJs will experience a cracked 0331 cylinder head and the #1 symptom of that problem is "unexplained coolant loss". You should educate yourself on this issue. Google search is your friend here. Google "jeep cherokee + 0331 head crack" and you'll have lots of threads to read.
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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 search will show you why.

01cherokeeguy

I suppose this could be a possibility but the previous owner had it since around 100k, and he left me with plenty of records of oil changes he had done.

Thank you very much sir! As far as the spark plugs go, about how much would it be for the ones you recommended, and what does it mean exactly to have them gapped to .035? Are they somewhat easy to install?

Thanks again man, I appreciate the helping hand

831xj

Spark plugs are about as easy as it gets for car maintenance.
Super basic on the 4.0

Google it you can find videos/tutorials that will explain it

Radi

Figure about $2 each for the plugs, give or take. You'll also need a spark plug gap tool, most places have those up near the cash register for about a buck. It's a simple feeler gauge that measures the space between the two spark plug electrodes.
You'll see .035 marked on the gauge. That part of the gauge should fit snugly between the electrodes.
You'll also need a spark plug socket and socket wrench if you don't have those.
Cold engine- remove plug wire, blow dirt away from base of spark plug, unscrew the old and screw in the new. Move on to the next.
As mentioned, I'm sure you can find a video of the process somewhere if necessary. It's pretty simple on the inline 6. the plugs are all right there.

Turbo X_J

'01 no wires, cap, distributor.

Radi

Oh, good call, lol. No plug wires to remove to change the plugs, gotta remove the coil rail instead. IIRC 4-13mm bolts

01cherokeeguy

You guys rock, thanks a lot. I am sure I will have no problem with changing plugs, I have done far more technical things on some of my cars with less help although it took me a while to figure things out..

I will report back and let you know if the plugs solve the problem. I have a good feeling that they will!

investinwaffles

Make sure you have a nice long extension, and possibly a ujoint or wobble joint to help angle the socket into the spark-plug port. And some little anti-sieze when you put it back in.

Thread and snug them up by HAND with the ratchet extension, then tighten them a full 1/2 turn. Run the motor for a few full heating/cooling cycles and tighten them another 1/4 turn. Thats how I have always done it, and I have never had a problem or stripped the threads in the head, but I am only 130lbs so if you have gorilla arms go easy on the spark-plug threads in the head.

Or torque to 13-16 ft-lbs with a torque wrench if you really want to be accurate (I also verified this, and one was not as tight as I thought it was, always good to check).

Injectors are easier to swap than the fuel filter/check valve assembly, so I would start there. Not gonna hurt to swap in some new injectors at 160k miles.

landude

You said the PO had records about oil changes but how about coolant maintainable?
For that year it's something big and needs to be taken care of/watched for the good of your XJ. Take care of it properly and it will get you there..
Put a little anti seize on the plugs when you put the new ones on...

01cherokeeguy

Well the mechanics I bring my cars to are pretty competent and I brought the Jeep there initially to do a vehicle inspection before I bought it. And it has been there since for oil changes, etc. and I am going to go on a whim and assume they would have noticed anything major like that. I will check my coolant situation when I do the plugs this week.

Thanks for the input!

01cherokeeguy

Checking back in guys. Put new champion plugs in this morning. They did not have the ones you recommended tj. It was quite an easy thing to do.

After I put the new ones in and put the coil back on I started it up and there was no more check engine light. I drove it a bit afterwards and it seems to be running much better. The help is very much appreciated everybody.

A few questions though. I was kind of in a hurry to do the whole job. At the parts store, the guy said the plugs came pre gapped to .036. I assumed this was close enough to .035 and I just put them in as is and the parts store guy said they would fit.

Also does it matter how snug they are? I tightened them by hand initially and then finished them with the socket wrench but I didn't tighten them as tight as I could get them because I didn't want to to break them or anything. They are definitely not loose though.

Also as far as coolant, what would be an indicator of it being bad?

Thanks again

landude

Since the coolant situation is unknown I would at least drain the radiator and put in fresh. Or Better yet flush it all... Pull the lower hose to do this, not the drain plug on the rad...

investinwaffles

I honestly would have gapped them to be doubly sure (especially when trouble shooting). Fitting size wise is totally different than what the spark plug gap dictates, but as long as they all looked to be the same gap it should run pretty well. The parts store guy mostly just wants to ring you up and doesn't give a rats a$$ about what they are gapped at though, so dont trust them too heavily.

As for tightness, like I said - tighten them till they are snugged up to the block and then tighten another half turn (I believe the champion's have that written on the box as well).
For reference, 15 ft-lbs is not very tight (your lugnuts should be torqued to 100 ft-lbs, which is tight as *****). The spark plugs wont break if you overtighten them, but the threads within the head will strip which is infinitely more of a PITA to rectify.

Coolant, look in the overflow reservoir to make sure its bright green and clean, and do the same under the radiator cap when the engine is cool enough to open it. Brownish or with particulate floating around -- flushing it would probably be advised.

EDIT:
And if the radiator is original, DO NOT TOUCH THE DRAIN PLUG. You will crack it by even looking at it and I ended up replacing my radiator (doh!). Unhooking the lower coolant hose is the easiest and cleanest way to drain the system. Flush it out thoroughly with the hose, and buy several gallons of distilled water. After the water from the hose comes out clear, fill it up with distilled water and let it get to temp (blower + heat set to high). Drain + fill twice with distilled (or until it comes out clear), then refill the system with antifreeze mix.

DOUBLE EDIT:
Also try to reset the PCM/ECU and reset the engine parameters to factory. Might help with the rough running if you haven't tried it yet.
http://www.quadratec.com/jeep_knowle...article-89.htm



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