Hi

I had similar problems on my lifted 93 YJ, 4.0 liter.
It took awhile to troubleshoot, but after replacing ignition,
wires/starter, emissions, fuel filter, fuel pump, it turned out to be
the OEM factory computer. This was a year after the engine had been
replaced, fuel injectors cleaned, new plugs, wires...

the funny thing was I took it to the local jeep dealer, who couldnt
find out what the problem was. This was after they ran diagnostics,
and checked emissions, and exhaust. <I thought it was the catalytic
converter clogged> and billed me an extra $200 just to tell me nothing
was wrong.

the problems were it didnt matter what the engine condition was, after
running awhile the computer would just short out, and I would be
stranded. It literally was like a lottery as to how long the engine
would run, it could be 2 or 20 minutes before stopping. Symptoms would
be sputtering and misfiring and loss of oil pressure, and then
shutdown.

I think the reals reason that the dealer couldnt find anything wrong
with it was because, if its computer related and the computer talks to
their computer, it creates a false positive effect.
also, I think that experience and training was also key. People with
little experience in diagnostics tend to blame the equipment and not
themselves.

hope this helps.


NT wrote:
> Hi:
>
> Update on my troubles...
>
> I finally got around to taking the truck into the dealer today. The Dealer
> ran all possible sensor tests and checked the fuel pressure and spark and
> couldn't find anything wrong. The problem is still there (as far as I
> know). The problem seems to happen when the engine is thoroughly warmed up;
> on the drive over this morning, I guess it didn't warm up enough as the
> problem wasn't there - but it was there on the weekend when I was out on the
> highway. The dealer assured me that they warmed the engine up thoroughly
> and still couldn't find any problems.
>
> Not sure what to try next. I'm a little leery about starting to replace
> sensors and the like when the analyzer showed nothing wrong. The Dealer
> suggested that it could be the CPS (which has never been replaced) but when
> checked it seemed to be working fine. If the CPS is being flakey - why
> wouldn't it have been apparent when the dealer warmed the engine up for the
> test? - Maybe it's a vibration thing?
>
> I've discovered a little more about the symptoms.......
>
> The engine idles fine and runs well at all speeds and acceleration rates
> when cold.
>
> Once warm (either that or it's a distance thing), there is significant
> stumbling (feels like all cylinders are cutting out not just one or two) on
> mild acceleration, although, if I hammer it down, there will only be slight
> stumbling and it will accelerate like normal. Even though slight
> accelerating will cause it to stumble heavily, I can very slowly bring it up
> to highway cruising speed and it will cruise just fine - but hit a slight
> hill and it starts to choke!
>
> Once this problem starts happening, the idle becomes very rough as well, but
> it doesn't stall (at least not yet), but it does sound as if it's not
> running on all cylinders.
>
> I wondered if it could be some moisture in the gas. I was low on gas so I
> added a half tank and poured in some injector cleaner that is also supposed
> to take moisture out of the gas and that didn't seem to make any difference.
>
> Anyone else have any comments or suggestions?
>
> Thanks.
> --
>
> "NT" > wrote in message
> ...
> >
> > Hi:
> >
> >
> >
> > I'm hoping some of you XJ fans can offer some suggestions on a problem
> > that just happened to me today for the first time.
> >
> >
> >
> > First of all, the specs: 1989 Cherokee LTD (XJ), inline 6 cylinder, 4
> > litre, with 150k Km's (ie: relatively low mileage, or more accurately
> > 'kilometerage' for the year).
> >
> >
> >
> > I drove to Costco this morning, about a 15 km drive. Everything was fine
> > on the drive there but when I started the truck up to come home (1/2 hour
> > later), it was idling roughly and would stumble quite a bit while driving
> > (but it didn't stall) - it felt like it wasn't running on all cylinders.
> > I did make it home where I did a thorough once over of under hood wires
> > and hoses and couldn't see any obvious problems.
> >
> >
> >
> > The last time I drove the jeep was about 3 weeks ago. It's rained a lot
> > since the so it could be that some water has got into the gas tank, but
> > I've lived here in Vancouver for over 20 years and the constant rain we
> > get for 9 months of the year has never been a problem before.
> >
> >
> >
> > My XJ has never failed to start since I purchased in new in 89, however
> > after it was a year old, it began to take a bit of cranking (say 20
> > seconds) to get it going. It's been that way ever since. I took it to
> > several dealers all of who said that a bit of cranking was normal. Since
> > it wasn't normal when the jeep was new, I've often wondered if the CPS was
> > faulty, but in all the reading that I've done, a faulty CPS seems to
> > manifest itself in intermittent start failures and I've never had a start
> > failure.
> >
> >
> >
> > Anyone have any suggestions on likely candidate for the source of my
> > trouble? Thanks for any advice.
> >
> >
> >
> > Regards,
> >
> > Dave
> >
> >
> > --
> >
> >
> >