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[just-boot-it]

My 4.0 XJ started to misfire under load a few weeks ago as soon as it got hot, like I said only in drive not park or neutral. So I though coil? Cheked it today and there is a little resistance (.50 on 20k ohms??) so not sure if this is good or bad, Plugs look a little sooty from the rough running, leads are about 2 years / 10k old, dizzy and rotor the same. Now it misfires in park as soon as the temp gets hot ( 2 mins ) wtf??

Thinking coil still or something else? 

[bgbazz]

Does the coil feel really hot when the misfire occurs? If so, I'd say you found your problem.

[Dave69]

Roughly 1 ohm on the primary and 12,000-13,000 on the secondary.

have you checked for cracks in the insulation of the coil and leads etc. engine moves under load and opens break on a lead

[just-boot-it]

I haven't checked the coil for the heat build up baz so thanks for the heads up. I read somewhere if you earth out an attached spark plug on the block it should spark blue not red so then you have poor ignition. And the leads all looked good visually. I had resistance readings of between .50 and 1.50 on the 20k ohms scale on the HTs so I take it they are ok?

[bgbazz]

Only reason I mentioned the hot coil was that a few years ago I had a similar problem with a Chrysler Hemi and it had us all scratching our heads, until I grabbed the coil while fiddling around looking for loose wires etc...you can bet I'll never do that again!!!!

Anyway, new coil solved that little hiccup.

[just-boot-it]

Found a new delphi one on ebay for £21 with returns accepted. Worth a try.

[bgbazz]

Hope that solves the problem for you mate...did you ever get that CB working properly?

[just-boot-it]

Ah yes!  Works a treat mate, very clear and got it to work upto 8 miles through a town centre. Had a few of the guys try and fine tune it with their swr's as it was out abit but I found it sweet.

[bgbazz]

That's good to hear mate...the skip has been working very well over the last two weeks or so and I often listen in to chats between the UK, USA and Canada. Australia comes in quite clear sometimes, but not as often. What is your main call channel and what callsign do you use?

[Hillbilly]

My 4.0 XJ started to misfire under load a few weeks ago as soon as it got hot, like I said only in drive not park or neutral. So I though coil? Cheked it today and there is a little resistance (.50 on 20k ohms??) so not sure if this is good or bad, Plugs look a little sooty from the rough running, leads are about 2 years / 10k old, dizzy and rotor the same. Now it misfires in park as soon as the temp gets hot ( 2 mins ) wtf??

Thinking coil still or something else? 

Had something similar. Popped the hood after dark and saw one of the HT leads shorting to the block. HTH

[demonicwillow]

If you find it isnt the coil, check out the CPS, they can be fine when cold and play up when warm/hot, one way of checking is to get the engine up to temp so it plays up then carefully hose the cps to cool it, then drive it n see if its ok, had this a few years ago with an old 760 volvo of mine, volvo couldnt trace the fault but an rac mate reckoned it was one of the cps's at fault, thats when the hose idea came to me, works a treat too.

[daggie]

 

[just-boot-it]

Update on said issues, new dizzy cap and rotor did a little to improve things so I fitted a new coil ( £33 ) and after a few coughs and splutters it ran up to tempreture for about 20 mins so I took it for a quick 15 minute blast and it only hesitated a couple of times.

The battery is KO'd I recon as it's been stood for 3 weeks and only started with jump leads twice. The plugs are a little black so may fit new ones soon, however they look to have no damage??

I'm 99% sure the coil was at fault as it improved the running dramatically.

[Dave69]

good result then,

If the battery has been flat the jeep will run a bit rough until it relearns it's base settings then it should be fine again

[just-boot-it]

Further update - still fooked runs sweet when cold but when it gets up to temp it misses, if you hold the throttle cable open with your hand it revs and then nearly stalls. Thinking sensors or fuel pressure now. Got to go into work on my day off to sort it 

[isle of man]

Cat blocked !!

[Dave69]

get engine warm run at fast idle, if cat is blocked then that down pipe will start to glow brighter than rudolfs nose on a cold night

[Hillbilly]

 Might have missed this, but have you checked fault codes on your Jeep

[JamesH]

Check fuel pressure too if you have a gauge or can buy or borrow one, it was the problem I had

[just-boot-it]

Yes I checked the fault codes at work and none came back. I'll be borrowing a fuel pressure gauge soon to test it.Swapped map and tps sensors with spares a friend had and no change in rough running.

Parked on a downward slope today with the engine running fine, into reverse and it runs shit. Looks more and more like fuel pressure methinks. I've changed enough leccy bits maybe I should change the thread title to XJ woes 

[bigjeepzj]

XJ do suffer from fuel pump probs

[just-boot-it]

If it is fuel pressure and there is no blockage is it worth changing the entire sender unit or just the pump section?

[bigjeepzj]

porb best change the lot as you have to take the tank off

[Dave69]

fuel pump is linked to the sender, the access might be on the front of the tank rather than ontop

[daggie]

its a tank off job