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[loosenup]

Hi guys
I Have a 2000 reg xj 4.0ltr orvis which has a missfire problem .
It starts no probs but runs lumpy , and has quite a serious missfire under acceleration.
I have checked all plugs , checked leads ( no visual signs of damage ) checked and cleaned dist cap .. no cracks .
any idea before i start taking bits off to replace?
I have searched the forum and nothing specifically comes up other than a suggestion of the upline O2 sensor which i am gonna find and disconnect so see if it is that
thanks
Phill

[JamesH]

I would replace distributor cap, rotor arm, plugs and leads unless you've done them in the last year or about 10k miles. They aren't really expensive parts and mean that system is correct and good condition.

Check for any split hoses or connectors on the vacuum pipes on the inlet also.

Could be o2 sensor but I've been down that route myself and it wasn't the answer.

Before all this scan for fault codes if you can

[loosenup]

hi James
less thank 10k since last change of leads and plugs.. just disconnected 02 .. same .. thinking TPS
or coil
cheers
phill

[Green Jeep]

You should able to get the fault code by holding the trip button down and turning the ignition on and off three or so times, dash gauge should flicker, then speedo will count 1,2, etc then give you a fault code which you can google.

I did this on my TJ and it came up with TPS sensor, plenty of info through google/this site

Good luck Maf

[loosenup]

hi Maf
Trip button .. what is where is this .. is in on the cieling mounted thingy in the middle

[loosenup]

righty guys
changed lead cap and rotor .. missfire gone .. only now i got check engine light lit
did the check thing with trip button .. nothing came up just goes back to normal wth the exception of the check engine light
phill

[Panic mechanic!]

disconnect battery for 5 min then reconnect see if it goes out

[Jonny Jeep]

Pressing the odometer reset button while turning the ignition on puts the cluster into it's test mode. For codes, if the PCM allows it (doesn't work on 98-2000 Wranglers), within five seconds and without starting the engine, turn the ignition on-off-on-off-on if that doesn't work try turning it to on five times rather than three which I believe some later Chrysler group vehicles require.

[loosenup]

Update
changed all the leads and dist cap and rotor .. as i said light came on .
drove it .. missfire gone .. light still on.
parked.. started engine again .. all lights normal no missfire .. running like a dream .

mystery

thanks for all the replies

I have a TPS coming next week .. i will fit this as a matter of course now see if it is even better

Happy new year to you all

Phill

[JamesH]

Good work