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Please help with diagnosis...

Hi, I've got a bit of a problem with my 98 TJ 4.0l 5 speed.

Here's what happens...

Around town, all is fine, but once I get on the highway for a while at consitantly higher rpms...around 2200 or so..at 65mph in 5th, it will randomly, and without notice suddenly start to sputter, does a small backfire, and the rpms drop immediatley. Adding gas does nothing but drop the rpms faster, and all I can do is pull off the road before being forced to a stop in the middle of the highway. It doesn't die, but will just sputter away at just under regular idle speed. I have found that I can shut it off, and let it sit for a minute, then restart..(no problems restarting), and I can sometimes continue for a while, sometimes just a few hundred yards before it does it again. If I can get to an exit, I can drive it all day around town with no problems.

Here's what i've done so far...

I changed the plugs, wires and distributor cap...no effect

It did it once on the way to a job appointment, so I had to limp it to the nearest dealer, and got a quick rental while they took a look at it. They of course could not duplicate the problem, but they ran a minimum air flow test and it failed that, so they did an induction service, emisions flush, and clenaed the throttle bore and induction system of carbon deposits. $125...I was glad to get out of the dealer with a bill that low..lol, and I hoped that just maybe, that was the problem. Yep, you guessed it...no effect!

Has anyone experienced this type of thing before, and can advise me furthur?

Any help is appreciated.

Regards, Kelly

Reply to
Kelly J
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hi kelly, my money says your catalytic converter is clogged.

Reply to
Nathan W. Collier

also..........might could be fuel pump........

Reply to
Carlo Jr.

There are many responses from CAT to fuel pump. You have a 1998 and I can't see the CAT being bad and if it was the fuel pump, you wouldn't be able to drive around town or anywhere.

I think you have blow-by into your intake. Have you checked your air filter lately? You will probably need to clean or replace your CCV and the hoses. The intake hose to the valve cover too. You should also inspect your ribbed intake hose going from your air filter cover to your throttle body for cracks or looseness. Also check your MAP sensor module with a vacuum pump to see if it's holding vacuum.

You did okay with the electrical, now try the intake side.

Reply to
Peter Parker

I'd guess clogged cat, clogged fuel filter, or fuel pump getting ready to go on vacation. Dunno if a jeep will do this, but on a Mazda, attempting to limp too far with a clogged fuel filter resulted in cooking the front catalyst to an early death.

Reply to
Lon Stowell

Reply to
L.W.(ßill)

hi bill, im curious about your recommendation. every CPS problem ive ever found, the CPS was either good or bad......ive never seen it run fine at 1 rpm and poorly at another.

Reply to
Nathan W. Collier

Reply to
L.W.(ßill)

LOL....Thanks folks! Allot of possibilities indeed!!! I do appreciate the input. I'll let you know what I find out...Wish me luck.

Regards, Kelly

LOL...Thanks>

Reply to
Kelly J

Reply to
L.W.(ßill)

Sounds like what happened to me on a Dodge Ram. That turned out to be a CPS. That took a while to figure that one out. I just put in an upstream oxy sensor in my 97 TJ having similar problems to what you described and what a DIFFERENCE!!! Of course I was getting the computer codes with the key telling me what it was. What do your codes tell you if any? Good luck,

Kevin

97 TJ
Reply to
Kevin KC8GAB

Had a CPS problem, ran fine most of the time...then on occasion it would hesitate, back fire, dog down, etc. Granted this was mostly when I put my foot in it, but not always.

Reply to
jbjeep

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