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'97 XJ 4.0 running rough, stalling and missing


 
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cartman
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Joined: 06 Apr 2005
Location: Salisbury, Wiltshire. UK

PostPosted: Wed Jul 20, 2005 12:26 am    Post subject: '97 XJ 4.0 running rough, stalling and missing Reply with quote

We had LPG (liquid petroleum gas conversion) fitted a few months back and in conjunction I upgraded the ignition system. Accel coil and leads and an uprated dizzy cap and rotor arm.

It was running fine. Stonkingly in fact. But over the past few weeks it has started doing the following:-

Lumpy running at tickover & engine cutting out & missing under acceleration. All of these were intermittant faults and sometimes it would run fine for 3-4 days, then the cycle of problems would start again.

I dragged the XJ around to the gas installers who could find no fault with the LPG system but plugged in a diagnostic unit to look at the Jeep ECU fault codes. Two faults cropped up - ignition primary something and injector 2. Now injector 2 was a recent gas problem which has been resolved but the ignition was maybe the problem (I had reset the ECU by disconnection the battery just before fitting the ignition components previously)?

I also proved that the faults existed on both petrol and LPG after running just on petrol for a while.

Now the faults seem to be getting more frequent (last night it cut out 6 times on the way home) so I attempted to isolate the cause.

Fitted a new set of Champion plugs (RC12LYC) to replace the original NGK - No noticable difference. Replaced the Accell coil with the original Mopar item - no difference on tickover (lumpy'ish). Swapped the leads for the originals - slightly smoother and I reset the ECU again by disconnecting the battery for 10 minutes.

Took the XJ out for a 10 mile run without any noticable drop in power and it ran smooth. But as I said above it is intermittant so I won't know yet whether I have cured it.

Anyone experienced similar problems and located the fault to something other than the above?

From confused and I want my original Jeep back Evil or Very Mad
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1fox2go
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Joined: 01 Dec 2004
Location: Fishersville, Virginia

PostPosted: Wed Jul 20, 2005 7:52 am    Post subject: Reply with quote

try replacing the cap, rotor, plug wires all with new mopar....ive been told that new ingnition pieces that burn hotter pull too many amps thru the computer and burn out the computer
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96 Cherokee 7.5 inch TnT long arm Locked F/R, D44 rear, 4.56s, 35x12.50 Muds/36x12.50 TSLs
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ThePhantum
Pissed-Off Admin
Pissed-Off Admin


Joined: 23 Jan 2004
Location: I knew it...I'm surrounded by Assholes!

PostPosted: Wed Jul 20, 2005 8:28 am    Post subject: Reply with quote

Amps do not route through the ECU to get to the coil...so the upgraded ignition will not harm the computer.

Are you absolutley sure there's not a bad injector? The easiest way to check if one is bad is to disconnect signal wire one at a time and listen for any change in motor speed. If an injector is not functioning there will be no change when you pull power from it. Give it try, it's easy enough to rule out.

How many miles are on it? The symptoms sound like a classic CPS sensor problem...except the intermittent part. It might be that the coil is starved for power. You could try checking the grounds as well as the hot lead to the coil. Also try cleaning the throttle body (since you've got an ignition code, I doubt this is the problem...but it certainly can't hurt to have a clean TB). While cleaning it, check the IAC valve/motor and make sure it's not sticking.

Post up what the exact code is...that will help in diagnosing the problem. Wink
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cartman
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Joined: 06 Apr 2005
Location: Salisbury, Wiltshire. UK

PostPosted: Wed Jul 20, 2005 11:12 pm    Post subject: Reply with quote

Cheer for the replies guys.

Phantom - 59k miles.

Checked the diagnostic codes last night and all there was there was code 15 (batt recent disconn) and I did that anyway. Other than that just 55 'end of code' so no help from that then. Embarassed

As the fault is intermittant I will just have to wait for it to occur again and hope I can grab the code Sad

Cleaned up the TB and IAC last night and there was quite a bit or carbon build-up on the manifold side of the TB so I gave that a good dose of injector/carb cleaner. Also went through all the earths and refitted the new Accell ignition leads. Pulled the plugs to the TBS pos'n sense and, IAC and dizzy to check for anything obvious then cleaned and refitted.

Ran it up and took the XJ for a 10 mile drive followed by 35 miles this morning and it 'is' running sweet. But as the fault is intermittant - watch this space Wink
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