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5.2l runs really rough after getting to temp

18K views 22 replies 10 participants last post by  reeln1in 
#1 ·
My daughter has a 93 Grand Cherokee limited, 5.2l automatic, with 200k miles. The engine runs fine, smooth and plenty of power till it gets to operating temp(200*), then runs rough and acts like the timing is off. I have changed both cam and crank ps', rotor, cap, oil, air and fuel filters, plugs n wires, fuel pump, thermostat and ecu temp sensor, vacuum hoses, pcv valve, alternator and battery. I don't get any codes except 12 no codes and 55 end of codes. I am at my wits end!! Does anyone have any ideas or had this problem before?
 
#4 · (Edited)
I'll check the 02 as well as the rest of the sensors. I already had the throttle body and IAC cleaned at a shop. I have cleaned most of the grounds and will get the last 1 tomorrow. I do have a manual, but didn't think about the egr, any chance a bad at could be the culprit? I'll check those out as well. I'll post an update after I'm done. Thanks
 
#9 ·
Yesterday I started going thru all the sensors, the EGR and Crank sensors were up first and they were ok, but the TPS was bad this time. It has to have a short in it, my buddy and I checked it before and it checked out fine, but when checked last night it was bad, rechecked it 3 times and it was bad 2 of the 3. I ordered another but it won't be here till tomorrow morning. I'll let ya know how it turns out, Thanks.
 
#12 ·
I am thinking manifold air temp sensor. it should read less than 1000 ohms when the engine is warm. At 70 degrees it should read 3400 ohms. There should be a full chart in your book.
Also did you check the MAP sensor ground on the flywheel housing near the starter? Did you check/change the MAP hose?
let us know how goes.
 
#14 ·
I re-checked the map, mat, iac, egr. Replaced (with slight improvements but no fix) crank, cam, coolant temp, O2 and tps sensors, multiple vac hoses, thermostat. I guess that leave the ECU.

What do ya'll think about this...

The engine only does this when it hits 210* operating temp, if I replace the 195* thermostat with a 185* or lower, if it is the computer it should stop "craping on itself"... cause it shouldn't get to that temp, right? And if it doesn't do-it then that would be the computer.... right? or has my brain turned to mush and I'm reaching here...
 
#15 ·
A common problem with the 5.2l or 5.9l Magnum engines is the intake plenum gasket leaking. There is a steel plate bolted under the intake manifold that has a gasket that blows out causing an internal engine vacuum leak that effects one or two cylinders more than the others.

Another symptom of a bad gasket is oil burning, maybe 1 quart in 500 miles, usually not enough to smoke. You usually will see alot of oil in the bottom of the intake if you look down the throttle body bore with the blades held open. (Engine off please! :homer:)

Sometimes the oil injestion/vacuum leak will cause the engine to ping under load.
 
#18 ·
I had a similar problem and had to sync the disributor and it ran fine after that. The instructions are in the manual. It will run finr until it goes to closed loop and then start running like crap. Might be worth checking.
 
#19 ·
crzyxj has a good point in checking the sync.

There was a TSB to also check the distributor drive gear and bushing in the block below the distributor. There should be almost no play in the drive to block bushing vs the drive's shaft. There's a Miller special tool for replacing and burnishing in the new bushing, if needed.

Also, check the distributor itself for a worn shaft and/or bushing that can throw off the sync and/or cam sensor signal.

Here's a link to the TSB:
http://dodgeram.info/tsb/1993/18-08-93.htm
 
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