Hi guys I'm an owner of a 5.9 slt+ 4x4 with 160K on the ticker and I'm having some problems.

Every time the car warms up to normal temp it starts to hesitate and buck on acceleration. There is also a sense of a considerable loss of power and there is the occasional back-fire. Its particularly bad on hills. It feels like the transmission doesn't know what gear to choose or something. The thing runs fine when it's still cold though. It's only until it warms up.

I thought it might be the transmission but it works completely fine if i drive the car without warming it up. I also thought it might be spark or ignition but the plugs look fine as they only have a few thousand miles on them. The plug wires are MSD and they are pretty new too.

My guess is that it could be something in the emissions since it varies with the warm up of the engine (like egr and pcv). What do you guys think? If so, where are the egr and pcv on these suv's?

Oh and there is no check engine light.

Thanks fella's

 

Are you using platinum plugs?

 

sam asks a very valid question platinum plugs do not get along well w/ these engines for some reason, just trust us, the cheapo copper core champion plugs are the best for these trucks, also check that the gap is correct .040

there is no egr valve on these trucks, im not sure where the pcv valve is, but i doubt its causing your problems

it sounds to me like its the pre-cat 02 sensor, simply bc when cold input from the sensor is ignored until the engine is warm, then it is supposed to control the a/f mixture based on how much unburned fuel there is in the exhaust, or how much extra oxygen is in the exhaust. that would be my starting location

 

Im using copper "truck" spark plugs. I didnt check the 02 sensors only because there is no check engine light but i guess it cant hurt. Still, what could cause a car to run fine when its cold but like crap once it warms up.

Sometimes when im coasting down a steep hill and the temp gauge goes down a little the problem will go away for a bit until the gets back to temp.

 

Sounds like a plugged CAT to me or muffler!


Take it to a muffler shop and ask them to check the back pressure before and after the CAT. Most shops will do this test for free.

 

It sounds to me actually like the pre-CAT O2 sensor and if it keeps up it will be your CAT aswell. The backfire you hear is most likely unburned fuel combusting in the exhaust due to running rich and that leads me to believe it's the pre-CAT sensor.

Replace it with a dealership sensor whenever you can, but make it sooner than later. Don't simply put up with the problem or you will burn out your CAT converter. This same problem happened to me.

Also, check the wire looms below the power steering pump. This seems to be a common occurance around here at this time where the pressure switch for the power steering will leak at the seam and cause fluid to leak down on the wires below it, which is where the O2 sensor harnesses are located. They are not located there persay but it shares the same harness and it is known to run fluid down there and cause issues.

Also, keep your eye out for a MIL. Likely sooner or later a P0132 or P0138 code will pop up and if this is the case, yes it's one of the O2 sensors going haywire.

 

My Durango didn't throw any codes when my pre-cat O2 sensor needed replaced. Once it was the Durango purred like a kitten once again.

 

+1 hydra with the clogged cat. when its hot open the hood and see if the headers are almost or are red hot.

 

Thanks for the input fellas! I'm going to replace both 02 sensors, make sure the wiring below the power steering is ok, and see if the cat is clogged.

Im positive it has to do with the emissions system only because this problem is directly correlated with the temp of the car.

I'll get back to you guys with my results.

 

Well guys i replaced the front 02 sensor and the D runs muuuch better. It put some pep back into the truck buuuuut the problem still persists. The bucking and hesitation is still there but its less often and is now limited to gear changes, particularly down shifts, which now points me to my transmission. I had issues with the tranny in the past such as 3-4 gear shift problem so i'll prob be cruising the message boards for transmission woe's and fixes. Speed sensor? Rebuild?

On a side note. I recommend changing out your pre-cat 02 sensor if yours is old. It feels like i have a new engine. Autozone has a 02 sensor kit you can rent for free that includes several sockets perfect for the job with a slit in them to make way for the wires. Very handy and time saving.