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88XJ Shuddering on highway...help?

88jeep

NAXJA Forum User
Location
Mississauga, ON
alright.....here is what i did today:

Plugs
Wires
Rotor
Cap
Fluid Check and level off of all fluids
TB cleaned
Fuel Filter replaced

i am STILL having the same problem i was having before....when i get up at highway speed (100km/h ++) the vehicle starts shuddering and jolting back and forth kinda like it is trying to find a gear to coast in. This is ONLY when i am holding the accelerator steady at any given speed over 100kmh. Normal driving conditions on regular roads cause me no problems at all.

By the way its a 1988 Jeep Cherokee Limited Auto 4.0L 4x4 with 200k

i appreciate ANY other help you can offer on this...im stumped

Thanks

Pete
 
My 88 would buck at around 2000-2200 RPM, with a steady throttle (relatively high vacumn). It would occasionally buck at slightly lower or higher RPM's but to a lesser degree. I could accelerate through the problem RPM area and hardly notice, during city driving. My motor would only accelerate to around 3500 RPM, in fourth gear and would then crap out rather quickly. it seemed worse, when I used the throttle gradually (or relatively high vacumn) and would get better with the throttle opened quickly (lower vacumn).
If this sounds familiar, I'd check the O2 sensor (mine was failing). Then the wiring from the front of the fuel rail down the front of the motor and see if it has been fried on the exhaust manifold. Clean the connectors on the bottom left of the motor, knock sensor, temp. sensor and O2 sensor. And clean the grounds at the dipstick holder and the block to firewall.
There are other things that will cause these symptoms or similar problems. In my 88 I had a flat spot in my TPS, that seemed to affect the timing. The motor would buck at around 1/3 rd throttle.
I had a 87 that required a TSB, distributor re indexing. It would buck at highway speeds on occasion. Though it also had a O2 sensor recall, that was fixed at the same time.
 
Mine had similar symptoms, bucking when holding the throttle steady. I did everything that you have done, except fuel filter, and like yours, it still happened. I replaced the TPS, and it cleared it up for me.
 
ok....so is the TPS something that is hard to replace? where do i pick up a new one and where abouts is it on the engine?

Thanks again

Pete
 
The throttle position sensor is on the front of the throttle body. The two screws (torx) holding it on can be a problem. Many people have snapped them off.
Do a search on TPS adjustment and check that first. You might also try cleaning the two connectors for the TPS. before you buy a new one. There are a few connectors between the TPS and the computer, that get corroded and mess up as often as the TPS itself.
The TPS is water sensitive and often acts up after a motor wash. Most guys wrap them up in plastic and avoid spraying carb cleaner on them when cleaning the throttle body. I wrapped mine in tin foil last time I cleaned the TB and still messed it up.
Your problem may be something else (O2 sensor) or even a combination of things.
The TPS sensor adjustment is hard to explain and fairly easy to do, if you have a digital volt meter.
 
alright...i went in to get it scanned today and i will write exactly what they said was wrong....maybe soemone can give me some insight!

"Scan Test surges highway speeds...DRB test performed self test passed...TPS was out of adjustment readjusted to 12 Percent as it was at 16 percent partial.

Test Driven @ highway speed 110 km/h feels like possibly tranny related / mount problem / air box blow by from engine"

The guy said that i would need to get new motor mounts x 2 and the trany mount. He said it was possibly the tranny mount that was causing the shudder as no codes were recieved.

So....question is anyone know how to do motor/tranny mounts? are they hard to do?

All i can say is at least now i know that it isnt engine related but im concerned about teh tranny....also i am not sure how much work i actually wanna put into this as i am thinking of sellin it in the spring anyways.....

Thanks!

Pete
 
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