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[Brynjaminjones]

Afternoon all...


I just fired the XJ up after sitting for a few days, and it was quite badly misfiring at idle. I give it a gentle rev and it was running just as rough, then as midway through pulling away it was like someone flicked a switch and it was fine again. I stopped at a shop, started it up again 20 mins later and it did the same again.


It also did this once a week or so ago, but hasn't since.




Plugs, dizzy cap and rotor are all under a year old, am I right in thinking CPS or something along those lines??
Also, how do I go about trying to get it to show up codes?? I've tried the ignition tricks, but I can only get it to do a self-check of the gauges!

[wildwood]

TPS is the likely suspect.

[isle of man]

Dizzy cap, WD40 is your friend.

[gordy]

Sounds just like my issue, not every time but quite often when cold, foot on the throttle get hesitation and bucking, sometimes get popping or backfiring in too around the cat, but not proper backfiring out the tailpipe, then suddenly like the flick of a switch it's gone! and she roars off, initially did it once Jan this year then a few weeks later did it a gain and now more often, once warmed up runs great never did get to the bottom of it, put an OBD II scanner on and only fault was variable speed sensor and that was a one off never to return, plugs, rotor arm and distributor cap replaced.  Throttle body and IAC cleaned etc, it's a dodgy sensor, which one goodness knows if you find out let us know, cheers.  Googled, this is a very common problem, many threads in the USA, fixes range from cat to one of the throttle body sensors to O2 sensors bla bla bla.  Runs great warm so will suck it and see.
My thread:
http://www.birtydastards.com/frm/index.php?topic=23022.msg270374#msg270374

[Brynjaminjones]

Cool, thanks guys. I shall do some investigating when it happens again. I'm not too concerned, as it hasn't lasted more than 10 seconds yet.


I doubt it's related, but worth checking - would having a cracked exhaust manifold have anything to do with this?? I noticed whilst I had the bonnet up with the engine running yesterday that the leak is quite a bit worse than it was!
I'm not sure if I'm going to leave it longer or get it fixed, as I think it might be using more fuel than normal!

[XJ Fan]

Could there be contaminants in the fuel? A bit of grit or something that temporarily blocks an injector or its' fuel line?

[Brynjaminjones]

I guess it's a possibility - I fill it up anywhere, and often run on empty!


I've just been out in it again today, a similar journey as yesterday, and it hasn't missed a beat!

[bgbazz]

Condensation forming inside the dizzy cap will produce those symptons Bryn..as IOM said earlier WD40 is your friend.

[Brynjaminjones]

Ahh, I read the WD40 comment, but didn't realise condensation was the reason!
Come to think of it this has only been happening since I last washed the XJ, and I was blasting the underside for ages with a hose (which I don't normally do), so there's a good chance water could have made it's way in the dizzy!

I don't have any tools with me at the mo', but I'll have a check when I'm home this weekend!

[bgbazz]

Do the business with the motor completly cold, pref first thing in the morning and if I'm right, the moisture will be evident inside the cap.


Good luck.

[XJ Fan]

You wash your XJ??

[Jonny Jeep]

There are two parts to the O2 sensors. The sensor itself, and the heater element. The sensors aren't accurate until they reach operating temp. Because the sensors are heated they can be used sooner which reduces emissions.

The PCM starts using the upstream O2 sensor for fuel mix data once a timer has expired. If the heater element is bad the sensor may not reach operating temp by the time the PCM starts looking at it. In that case the engine is misfuelled, and runs rough/pops/stutters/nearly stalls till the exhaust gases heat the sensor to it's operating temp and the engine smooths out.

To find out if it is the sensor you can unplug it and see if the fault occurs. The connector is clipped to a tab at the intake manifold near the firewall. Disconnecting the sensor will likely cause an O2 sensor code to be tripped. You can also measure the resistance of the heater element (don't measure across the sensor as it could get damaged). The heater resistance should be in the region of 5-7 ohms.

It happened to my 97 TJ years ago, and I got just a hint of it again last year so swapped the sensor again before it became an issue.

[Brynjaminjones]

I finally got around to investigating this - I took the dizzy cap of yesterday morning before I'd used the Jeep, and surprisingly enough there was quite a bit of condensation in there. After WD40-ing it, and also finding a spark lead that had a slightly dodgy connection, it was running even rougher for a while, but once that cleared it's been running uber smoothly!
I'll find out this morning if it's still good.



I also adjusted the kickdown cable whilst I was in there, and it's amazing what a difference that makes, even though it wasn't that long ago I last did it! 

[bgbazz]

Fingers crossed Bryn..tentative 

[ChrisS]

You've done the deed now, but was going to say, when you WD the dizzy, make sure you wait a few moments for the propellant to dissipate before you fire it up - watched a mate destroy the dizzy cap on a V12 jag doing that....quite spectacular! Probably would have been OK if the cap wasn't screwed down, but as it was, it pretty much just vanished when he touched the key and left a nice 'spray' of HT leads plugged into small fragments of cap. Wish I'd had some kind of camera with me at the time. He wasn't very amused.

[STUARTF]

WD 40
Never leave home without it
S