[19981]

I have a 1997 4.0L Jeep Cherokee Sport that hesitates until the car warms up. When I first turn on the car, it runs fine for a few minutes and then it runs rough for a few minutes. After this the car runs fine until you turn it off and restart after maybe 10 minutes.

When it is running rough, If I am in gear and press on the gas pedal, it seems like the engine is hesitating and I hear a knock that sounds like it is coming from the driver side wheel. This is the only time I hear this knock.

One other thing to note is that it certainly seems to be heat related. In the winter, the hesitation will not occur until the car warms up for 5 minutes. In the summer, the hesitation happens within a minute after starting.

Any help would be appreciated. We had the codes pulled and nothing comes up. I just replaced the distributor cap and wires and this did not fix the problem.

 

[krabysniper]

I cant swear to it but if I recall correctly the 96 and newer have heated 02 sensors, (I think) you may have one thats getting slow. Just a possibility.

 

[19981]

Thanks for the reply

Thanks for the reply. Do you know where I can find a wiring diagram to test the sensor? I checked the car and the sensor has four wires. I have a Haynes manual but they don't have the diagram.

 

[2293]

97 4.0 hesitation

You may have some slow sensors but before replacing them (after checking) try cleaning the throtle body with the right. I suggest you remove it from the intake, remove the electronic controls before doing a very good cleaning.

My 97 4.0 Sport also had some hesitation problems and this solved my problem.

 

[WilliamA]

Try doing a search for factory shop manual on our site. I think someone had posted that info before.

Kraby mentioned that the O2 sensors became heated in the later models. If you have 4 wires going to one sensor, I would think that is heated. I've heard that O2 sensors should be changed every 50k miles b/c they do get lazy.

As tincan mentioned, try cleaning up the carbon buildup in the throttle body with some cleaner. Remove it from the engine (and the sensors form the TB) so all the residue doesn't go into the intake manifold.

After that, you might want to try using some fuel system cleaner, like Redline fuel system cleaner Red Line Oil: Fuel Additives (I don't work for Redline, I just like their products)

You say you hear a knock from the front driver's side while accelerating, could this knock be pre ignition? Does this engine have a kock snesor? Have you tried a higher octane gasoline to see if the knock dissappears. If not, try running half a tank of some 93 octane to see if it goes away.

I'm not sure if that year had an egr valve, but if it does, I would check to make sure that is working too. You can see if it is working by reaching underneath and manually pushing the valve in with your fingertips. This is not a full test but at least you will know that the valve is not stuck. After that, you'll need a vaccum pump to test it further.

Let us know what you come up with.

 

[NIX]

Knock sensor and EGR were in the Renix system in the 87 - 91 systems if I'm correct. Not in a '97 for sure.

It sounds as a open loop problem. The O2 sensors only come in in closed loop when the engine is warmed up. But I can't think of a typical closed lop error to look for. Only thing I can think of is a clogged airfilter.

 

[19981]

Replaced the air filter still a hesitation, but thanks. Will most likely try cleaning the throttle body next.

 

[NIX]

There's only 2 things I can advise, more just to rule them out then as a certain couse for your problem:

1: check the grounds. Especially the negative at the batterie and the other end to the engine or body. Also check the strap between body and engine. Not just a look, bolt them loose and clean them and put some vaseline or other conservation on it. Same with the ground from the wiring loom. You'll find it at the dipstick stud at the engine or under the airfilterbox. 4 thin black wires tied together to a ring.

2: solder the wires form the CPS to the loom instead of using the connector. My XJ had a very occaisionally hestitation and this cured it. The GF mentioned the milage went up from 250 miles a tank to 300. Never would have expected that and I have seen this advise so very often. No idea why I neglected it.

 

[19981]

One other thing worth mentioning is that over the last year the check engine light has been coming on once a month for a few days and then the light would go out. While the light was on, the hesitation did not happen. Once while the light was on, I pulled the trouble code by switching the ignition switch on/off. One code that came up was P021 which the Haynes manual says is "oxygen sensor or circuit". I have not seen the check engine light come on for a couple of months now though.

 

[19981]

Problem Fixed!

I finally fixed the hesitation problem that I have had for over a year by replacing the oxygen sensor that is located before the catalytic converter. I had thought this might be the problem for some time but was too cheap to shell out $60 just to test out a theory...

 

[NIX]

Oh, those O2 sensors...

 

[Rickcomanche]

Cherokee Hesitation

Thank you. I got tired of changing parts. I changed plugs,wires,cap,rotor,fuel filter,tps,iac,map,cleaned the throttle body and it was the o2 sensor in front of the cat.Many Thanks