WTF? Erratic, momentary loss of power at speed.
 

While driving at speed... my 4.0L Cherokee hesitates for a split second. On and off, erratically. Not predictable.

Fuel pump?

Ground fault?

Throttle body computer control failure?

At first I though, since the previous owner had let the car had sit for a year in the garage, that the fuel filter in the tank was clogged. I have not replaced that yet.

The engine may not be a 1998 4.0L. I bought the car from a skilled mechanic who I trust... who replaced the motor with less miles. Based on the engine code... its a '99. (At this point I don't want to bug him with the problem. It's my car now... you know?)

It has lots of new parts on the motor.
Alternator... AC compressor... water pump... distributer.... spark wires....

Any guesses?
Thank you.

When did it last have a tuneup ? Maybee the sparkplugs are worn ? Or maybee a infamous tps
Try pull any codes from the ecm. Missfires can have many many reasons, but with some more info, it will be easyer

I have a 1995 Cherokee 4.0 with 275,000 miles, and I'm having the exact same problem.
My jeep is well taken care of by myself and I e never had the.problem until now.
I noticed 2 days ago driving from work at cruising speeds I do lose power for a split second, it is completely random and its on and off and it is getting worse. At first thought I thought it might be the fuel pump, I believe it is.
When it was getting worse yesterday I pulled over and restarted engine and it was fine for about 5 miles and started jolting again.

im getting a similar problem but im only getting it at low speeds i thought it might be my tranny because i in first gear at low speeds its like i let off the gas and i cant hear anything coming from the engine and nothing happens until i let off the gas and hit it again (not hard) are we on the same boat or are we experiencing different problems?

Chech your o2 sensors. They can cause issues like that

I'd put it in nuetral and rev it. That should rule out the TPS since it's not necessary to monitor the TPS for transmission adjustments. If it persists, I'd say fuel pump. There's a lot of fuel pump failery going on right now, myself included. For the 3rd time I've owned this XJ.

I think it has to due with offroading and pump longevity. Also, bad fuel and sitting can have that effect, but this all points back to the fuel system (notice I said system). I would have someone check the fuel pressure while you're reving it at nuetral. If it's dropping below (I'm going to guess and say 45, 49 is what it should be at idle I think) then it's probably the pump or something in the fuel lines. I'd run some acetone/fuel system cleaner through it before thinking it's the pump.

That definitely sounds like a pump. When you start a vehicle, the fuel pump primes the fuel lines with pressure (and since the injectors aren't firing much just before you start it, it returns pressure to the system). Then as you drive the pressure slowly bleeds off because either A. the pump itself is failing, or B. the check valve isn't holding the pressure in the fuel lines.

I've been there 3 times in the last 4 years. I'm a fuel pump whisperer.

That is also true. I've been through 5 of those this year.

Only buy NTK (sold at NAPA) if you have to replace 02's. Stay away from Bosch if you don't like buying many 02 sensors.

That I am not familiar with... only low speeds. You need to check for codes.

Autozone will do it for free.

I have this same issue, there is like a slight backfireing from like 1400-3500 rpm UNDER LOAD and it sometimes lurches going up hills when its under 2000 rpm. I have replaced the o2 , fuel filter, used sea foam and nothing has helped this problem. It annoys the **** out of me!!

RIght as my pump was kicking the bucket for its last few minutes I had a lot of backfiring.

I've also had a bad crankshaft and bad 02 sensors give me this problem.

How long have you had the problem and when was the last time ANY maintenance was done to it?

A camshaft position sensor relays camshaft position for fuel injection/timing purposes. Of course if that's bad you'll get a code for it. Those usually don't go "bad" . If anything you might have a bad ground for it. You'd have to get a diagram for it though as I don't know where it grounds to or which wire it is. Maybe the Haynes manual has something on it.

I would go to autozone and have them pull codes for free. The codes are the only form of solid deduction. Nothing can be deduced from describing something as there are multiple things that can cause the same symptoms when it comes to just about anything.

These engines are controlled via electronics, and the only tool for electronics are scantools and OBD-II code readers. Until you see the codes there is no telling what is actually wrong, unless you have money to waste on randomly trying parts.

Even then that won't necessarily solve the problem as there could be something wrong with the wiring.

..what kind of 02 sensor? Just because you buy a part doesn't mean it works. The brand of 02 sensor makes a big difference. I haven't bought a bosch that has worked yet, front OR rear.

Before you buy parts troll the forums. I've spent hundreds in the past few months on parts that if I just would have done a search for I would have found that I shouldn't buy them because they either aren't going to work, or will work for a short period and I'll have to replace it anyways. Simply buying parts blindly never solves anything. About the only thing I can walk into a parts store and buy that I know I don't have to worry about are tools. Anything else is suspect to failure and should therefore be bought at NAPA. NAPA brand parts are worth every penny.

For all of you, if it IS the fuel pump... DON'T BUY AN AIRTEX.

I'm in the boat right now. I found out shortly after I bought it I f*cked up. Everyone who I talked to, who had had one, had to toss it and get a Bosch in the end. Bosch sucks for 02 sensors, but they make lasting fuel pumps. We do too much offroading in Jeeps for for Airtex to last.

So I bought and installed my Airtex May 11th. It just died on me 45 miles from the house on Thursday. I am now getting a Bosch (bought on Amazon for 260 with taxes and shipped to me the next day... ordered Friday afternoon, gets here tomorrow). Bosch bought from NAPA (Advance and Autozone only sell Airtex... so don't ever buy a pump from them) costs about 335 plus tax.

Another FYI, Airtex is made in Mexico. Cheap parts cost cheap money. And cheap parts aren't built to last.

Mine lasted right up until I really started wheeling again with my XJ. I haven't wheeled it since the fuel pump install. I just started last week. Now my pump is dead. Right after I just filled the bastard up too. Talk about PITA... fuel pump on a 97 and newer XJ requires dropping the fuel tank. Not only that... the pump itself is much harder to get out and put in than the 96 and older. I used to have a 93 and changing out that pump was a sinch. Coincidentally I also replaced that one right after I finished some hard wheeling. Came back down from Big Bear Mtn in California and it died on me in Lucerne Valley. Lucerne Valley is 40 straight miles of no cell phone service. I got picked up by some drug addicts in their late 30's in a small beat up 2 door saturn. Wasn't the most pleasant evening.

You can find a bosch online (Amazon is always a safe bet) for anywhere from 60-100 bucks cheaper than at NAPA, and have it shipped to you. Amazon charges next to nothing for shipping. I highly recommend you use it.

It's a 93 so reading codes isn't possible, the check engine light isn't on. It was been doing this for probably like 3 months. It has had a new o2 (Idk what brand) and a new fuel filter along with plugs and wires and a couple oil changes. What I think I have narrowed it down to is tps or cps or the fuel pump... all not cheap things

Pull out the 02. If it's not shaped like a perfect cylinder with holes in it, it isn't one you want. Gauranteed.

Your NTK will look like this:
http://www.drivewire.com/images/shop...1839947NTK.JPG

A Bosch will look like this:

http://www.ecatalyticconverter.com/i...osch/13122.jpg

If yours looks like the bosch, you have a problem there in and of itself. I had tons os misfire when I had a bosch. Then when I put in a new one it worked... the next day it was dead. Kept reading System Too Lean Bank 1. And yes it was the 02. I could smell horrible rich gas.

Haven't had ANY problems with the NTKs. I've had them in for over a week, so they've way outlasted all the Bosch's I've had.

If you have a 93 then you have OBDI. Follow these procedures (even if you don't have a CEL) and see what you got. http://www.jeepforum.com/wiki/index....k_Engine_Codes

Sometimes I hook up my code reader and see that I have codes even though I don't have a CEL.