Dealer cannot solve this one

[Sunbeam2]

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

[JDPascal]

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

[dksob81]

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.

[Sunbeam2]

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?????

[mx52nv]

tps, cat conv, fuel pump, iac

[Sunbeam2]

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

[mx52nv]

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

[Sunbeam2]

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

[mx52nv]

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

[Sunbeam2]

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

[Dale Aeppli]

Originally Posted by Sunbeam2

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]

[dksob81]

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.

[89ltd]

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?

[Cam7]

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.

[Sunbeam2]

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