Dealer cannot solve this one

After several hours of driving at turnpike speed the engine will suddenly buck and we cannot get the car to go over 55 mph. From a dead stop we have to slowly nurse it up to 55. any attempt tp go faster and the car stops running, if I back off the gas pedal it will run again same ot low speed if I push the pedal down it will quit, until I back off again.
no codes, normal temp. will not happen until after several hours on the road??????????????
1997 grand cherokee limited 5.2 automatic

What have they checked.

Could be fuel, could be ignition. possibly computer related but difficult to find when it is intermittent like that.

Could also be the catalytic converter.

I had one that was intermitent like that. When I cut it open, one section was busted up and partly restricting at times.

JD

I got a couple theories, too much Air (when throttle Open) not enough fuel to compensate. and/or to much Fuel not enough spark to combust the Fuel.

I would point more toward a Spark problem. Check the plugs they may be fouled, you might be getting early detenation.

I pulled the plugs they were OK almost perfect
I pulled the coil, cleaned it, checked with a multi meter, that was OK thinking it might fail hot , I heated it in the oven till it was around 200 degrees, the resistance was higher but still within limits.
When this problem starts after about 3 hours of driving and if I just push just a tad too hard on the gas it just quits, if I back off, it runs again. almost seems throttle related. What does the throttle position sensor control????? It does it when in gear, it revved right up in neutral
The dealer said that no codes showed up and they could only check it if I bring it in when I am having the problem, problem is when it starts I am in the middle of no where.
Dealer said it could be a sensor and it could be the main computer.
What are the most logical suspects?????

tps, cat conv, fuel pump, iac

what is iac??? There is a wire or plug in the cat Conv, what is that for????

idle air control valve. yes there is a wire going to your cat, it's to the o2 sensor.

I thought the O2 sensor was in the down pipe before the Cat Conv or is there two O2 sensors

have you ever even looked under your own Jeep???? And yes there are 2, 1 on the downpipe, 1 on the cat.

Gee I must have been under there becuase that is where I saw the wire in the converter. The manual I have does not show any wire to the converter.
can you help me to troublershoot this problem?
where should I start what should I do

Gee I must have been under there becuase that is where I saw the wire in the converter. The manual I have does not show any wire to the converter.
can you help me to troublershoot this problem?
where should I start what should I do

Have you checked the wiring to oxygen sensor and at sensor,could possibly be oxygen sensor related. Since it acts up after peroids of driving. Dale [email protected] :2cents:

96 and later - have 2 O2 sensor, 1 in the owwnpipe (determines the fuel/air micture) and 1 in the Catalytic converter (checks the operation of the Catalytic Converter). some jeep have 4 O2 sensors (California Emissions).

TPS - determines the ammount of fuel delivered to the injectors, depending on how hard you push the pedal.

IAC (Idle Air Control Valve) - allows air to by-pass the throttle plates while idling. - this would deffinately not be related to you problem.

I was thinking the egr valve could be opening to early , that would for sure make it bog down, but you say it is ok when revving the engine in neutral?

Does your check engine light come on? If it does what are the codes. The one thing that comes to mind is the cam position sensor it will usually cut off when it statrts to go bad and when it gets hot. You should do a fuel pressure test to see if the fuel pump is starting to go, could also be a bad cat, egr or even a PCM.

Ok the dealer said the fuel pressure was OK
I am NOT getting a check engine light and there are no codes.
One thing I did notice when driving and hitting small bumps there is a noise like a loose exhaust pipe.but I checked and they are secure
Will the check engine light come on if the O2 ??sensors is bad????
When the problem starts if I push the gas pedal too far it quits, could that be an indication of a bad TPS???
What is the life expectancy of the various sensors the car has 90L miles in it now??
Thanks for all the help we are now narrowing down the problem

Yes, I would first look at the TPS sensor on the throttle body. They are cheap to replace and easy, it sounds like its bad, and you could still have a bad part a nd not get a code. You can actually test the TPS to se if its working before you spend the money with a digital meter.

catalytic converter

Ok the dealer said the fuel pressure was OK
I am NOT getting a check engine light and there are no codes.
One thing I did notice when driving and hitting small bumps there is a noise like a loose exhaust pipe.

sounds like the cat is breaking up inside.

but I checked and they are secure
Will the check engine light come on if the O2 ??sensors is bad????

sometimes the CEL will not come on if the problem is not throwing a bad enough signal.

When the problem starts if I push the gas pedal too far it quits, could that be an indication of a bad TPS???

yes

What is the life expectancy of the various sensors the car has 90L miles in it now??

I think usually 40-60k

Thanks for all the help we are now narrowing down the problem

hope this helps you out

Ok the dealer said the fuel pressure was OK
I am NOT getting a check engine light and there are no codes.
One thing I did notice when driving and hitting small bumps there is a noise like a loose exhaust pipe.but I checked and they are secure
Will the check engine light come on if the O2 ??sensors is bad????
When the problem starts if I push the gas pedal too far it quits, could that be an indication of a bad TPS???
What is the life expectancy of the various sensors the car has 90L miles in it now??
Thanks for all the help we are now narrowing down the problem

regarding the noise you hear when you hit a bump, check to c if the muffler is tilted (it should be straight across) I had this problem mine was tilted sideway a lil and the exhaust was htiting off the rear axle.

check the cat. converter
A Good shop shoud be able to tell if you have a restricted exhaust.
Far shot check your distributer cap and rotor a bad cap/rotor can fail under stress.

What have they checked.

Could be fuel, could be ignition. possibly computer related but difficult to find when it is intermittent like that.

Could also be the catalytic converter.

I had one that was intermitent like that. When I cut it open, one section was busted up and partly restricting at times.

JD

Yup

JD

I cannot find any loose or broken wires..
What would be the first thing I should change to try to fix this problem??

I need all the help I can get, I am supposed to tow a boat 300 miles this weekend

With 90k miles have you replaced your ignition wires or are they original?
Old or cheap ignition wires will brake down causing loss of power under heavy load and still "look" good.
Also check replace ignition cap and rotor i had a 93 GC that would loose all power if i attempted to go over 60mph it had a broken rotor contact.

What do you mean by quits (boggs down or stalls?)

The thumping sound is common on jeeps with factory shocks.

The plug wires look brand new they are mopar wires, the plugs are bosch platinum and are perfect.

I will buy a new distributer cap and rotor and a tps and see what happens. The distributer is buried in the back of the engine and under part of the car, are there any tricks to get to that.

What other sensors can shut down the motor like that?? I was always under the impression that if a sensor failed the computer just used a default to run the motor

I'll guess from your response your not the original owner.
Unless the prior owner had dealer do tune up which i doubt (dealers don't use Bosch) those are the original wires and i would guess cap and rotor are original also.
the truck is 8 years old with 90k miles Start simple.

It`s the catalytic converter. Had the same problem. First it rattled on bumps for a while then the bucking. Replaced it and it was as new again.

I went to the jeep dealer for the parts, o-my-gawd $$$ the TPS was 79.99 so I went to NAPA their TPS was 59.99 then to Discount Auto Parts their TPS 25.99 it will be here this PM

Got the distibuter cap and rotor at the Jeep dealer 8.00 for the rotor and 25 for the cap, still pretty pricey.
Any tips on replacing that distributer cap, I can hardly see it. The thing is buried so far back in the engine compartment????

I changed the rotor and distributer cap, some burning on rotor and some wear on cap . Motor seems to start faster now. Still waiting on the TPS to arrive at my local parts store.
Is there anything else I can check while I am waiting????????

I have now received and installed the TPS, I am driving across the state this weekend. I will report back to let you all know if your help and advice on this problem has fixed it or if it still with me. Thank you all very much.

problem solved yea

problem solved yea
Great to hear you solved the problem.

The big question is was it the cap/rotor or the tps?

Doesn't really matter the truck is running and the fix wasn't overly expensive.