Check Engine Codes on 2001 XJ

Hello everyone,

Old member, got away from Jeeps for a while but recently picked up another XJ and need some help with engine codes. Quick run down...bought a 2001 XJ Sport, 4.0, 4wd, auto, and 165K. Got the Jeep for a project and the price was too good to pass up, so luck would have it that I am now having issues with it Check engine light was on solid when I bought it and the oil pressure gauge was maxed out (previous owner said it needed an oil pressure switch and a camshaft position sensor replaced).

Now to the real problem. The 3rd time I drove the Jeep, it started up, ran rough and the check engine light is blinking until I shut it off (limp home mode I believe). Had autozone runs the codes and here are the 6 codes that came up...P0300, P0301, P0304, P0306, P0456, and P1494. I believe that the P0300, 301, 304 and 306 are misfires in cylinders 1, 4, and 6 (can someone confirm this?). Should I start with new spark plugs or is there another route I should take?

The P0456 and P1494 are vacuum leak codes (I believe). Can someone confirm these? Where should I start with these?

Jeep is not a daily driver, so it doesn't have to be fixed right away. I am not a mechanic, but I don't mind getting my hands dirty and saving money on not having to have a shop repair it.

Any insight would be greatly appreciated as to where I should start.

Thank you,

Will

Check compression first off... 00-01s had a crummy head casting from the factory and misfires/running rough/blinking CEL are a sign that you need to check into it. Also check for coolant in the oil. Hopefully it's a sensor, but with signs of engine health issues it's best to find out right off.

You are correct on the evap codes, but definitely solve the others first.

Whenever I see a P0300 (with or without other single cylinder misfire codes), I look for a systemic root cause. Start by verifying fuel pressure. Must be done with a gauge. Many parts stores will rent you a gauge inexpensively. For a 2001, you should have 49 psi, plus or minus 5 psi.

And yes, you need to educate yourself about the 0331 head issue. Search is your friend with that; there are hundreds of threads on this condition on this forum and all of the other Jeep forums. Unfortunately, I haven't had the best luck with a compression test for diagnosing this problem. A leakdown test, cooling system pressure test, block test where coolant is tested for presence of hydrocarbons, and oil analysis are good tests for a cracked 0331. Some times the crack can be seen with the naked eye by looking through the oil filler cap with a good light or by removing the valve cover. They almost always crack between cylinders 3-4 on the 0331, which is where the head defect is located.

And yes, check for evidence of coolant in the oil and keep an eagle eye on your coolant reservoir as the #1 symptom of a cracked 0331 head is "unexplained coolant loss".

Good luck!

coil pack to repair the 3xx codes.

0456 and 1456 are evap codes. probably the NVLD switch

Pull the spark plugs and inspect them.

Compare:

http://www.google.com/imgres?imgurl...=n2rfUMrcMJG10AHR9IBQ&ved=0CFIQ9QEwCQ&dur=794

kastein said:

Check compression first off... 00-01s had a crummy head casting from the factory and misfires/running rough/blinking CEL are a sign that you need to check into it. Also check for coolant in the oil. Hopefully it's a sensor, but with signs of engine health issues it's best to find out right off.

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The cracked head wouldn't cause a misfire issue. It cracks on the top of the head leaking coolant into the engine. If the coolant leak is bad enough to cause a misfire issue then its time for a rebuild.
The misfires do lean toward a coil pack, especially since they are on 1 and 6, which share a coil. But first take a look at the spark plugs.

Talyn said:

The cracked head wouldn't cause a misfire issue. It cracks on the top of the head leaking coolant into the engine. If the coolant leak is bad enough to cause a misfire issue then its time for a rebuild.
The misfires do lean toward a coil pack, especially since they are on 1 and 6, which share a coil. But first take a look at the spark plugs.

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Very interesting, and very good to know!!!!

Definitely check the condition of the plugs--make sure you keep them in order while checking them.

That many misfires would make me suspicious of the coil packs, but test your way to the answer.

Also, the 00-01s have a heat soak problem, usually related to cylinder 3, there is a TSB floating around on the issue, but the factory "fix" is mostly a joke.

As this is a New to You XJ it may need plugs and coil packs--again, don't spend money on parts without doing a little work/testing first.

Good luck.

Thank you for all the replies. I will check the spark plugs this week and go from there. I will post up what I find.

Before I spent any money beyond fresh plugs, I'd reindex the camshaft position sensor. I am very familiar with the limp mode you're talking about. After a few misfires, the computer shuts off fuel to that cylinder. At one point, I was very good at dropping in to neutral, turning off the engine and restarting it to get all 6 firing again.

As for plugs, the recommendation I've gotten was AutoLite Platinum APP-985.

x2 on the cam sensor reindex. Don't get platinum plugs. There is no reason for them in this engine.

I don't have any 2001 rigs, but I run Autolite single Platinum plugs in both running Renix 87 and 89 XJs, and I have had no problems with them. Been using them for years with no problems.

Thanks for all the advice. Changed the plugs to cheap champions and the light stopped flashing

I was thinking it was either the plugs or a blankie stuck in the rear hatch. Thank goodness its only the plugs, jacking up a xj is impossible to figure out!

You're just jacking with us right? LOL

jacking up a xj is impossible to figure out

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