Drivability problem: 2001 Dodge Ram 1500, SLT, 5.2 V8, Extended Cab, 101,000 miles.

The engine starts up on the first turn of the key and idles smoothly. There is a momentary clatter of lifters which disappears as oil pressure builds.

The problem is that while driving at highway speeds, it bucks and shakes in the engine/transmission like the engine is momentarily shutting off or the transmission is locking up. It only occurs on LIGHT DECELERATION, like maintaining speed on a decline or lifting slightly to begin slowing for a stop. The only way to make it stop is to completely take foot off the gas, then it normalizes and smooths out. Also I can accelerate out of it with no stalling, It’s worse when using the cruise control because it cannot release the throttle totally and maintain the speed. The transmission shifts up and down perfectly and switching off the overdrive does not solve the problem. It does the same thing, just in 3rd gear.

What I have done: It sounded like it would be the TPS, so I replaced it. No change. Next, I removed and cleaned the throttle body, with no change. I replace the IAC with a brand new one. No change. There were no codes except for small and large Evaporative Emissions leaks (442 and 455). I found that there was a bad hose on the Charcoal canister, so I replaced that and reran the scan. No there are no codes at all, and the problem is still exactly the same.

When the engine is cold and still in closed loop this doesn’t seem to happen. By the time I get to a point in my travel where the engine acts up, it already has warmed up a bit.Fully warmed up the problem is always there.

What is different in deceleration…light throttle vs.no throttle input at all? Anyone have an idea as to what is going on?

Thanks in advance,
Andy

 

I'm still gonna vote misfires. Keep driving until you get a hard code (P0301 thru 0308) but you can likely find it sooner by looking for PENDING codes.

 

Has a tune-up with copper spark plugs, spark plug wires, distributor cap/rotor been done in the recent past? Also, any vacuum leaks?

 

Being a 2001, should be able to plug in a scanner, and have a look at misfire counters. That will tell you which cylinders are problematic.

 

When did this start? I asked the same question about '98 and was told it's virtually impossible save for a few professional level scan tools.

 

I’ll check for vacuums leaks. I don’t know when it was last tuned up. I inherited it from my father a couple of years ago and it had the problem then. He had had some mini strokes and wasn’t able to tell me much about the truck. Just that it had a problem he couldn’t figure out. I guess a tune up couldn’t hurt, but it runs fine other than the afore mentioned problem.

 

I have a small basic scanner. Not sure if it can do counting misfires or store pending codes. Is it possible to rent professional scanners which can read data live while driving and see what is happening when the problem occurs? I have little faith in the local Dodge stealership. They wouldn’t spend the time trying to figure out an elusive problem like this and would charge a fortune and replace parts in a shotgun approach. I feel I can sort it out better myself with the right tools.

 

The problem started several years ago before I inherited it. Actually I think my dad bought it that way from a local used car dealer. He wasn’t able to tell me much about it before he died. He didn’t really like the truck and didn’t drive it much, probably because of this problem. Once this is is sorted, I’ll fix a few small other typical problems and just enjoy it. Super low miles for its age, no rust, good interior, solid truck.

 

All scanners of which I'm aware have an option for pending codes.

I even have a ~$13 Launch that will pull misfire counts. You have to go to Mode 6 or look for anything like "onboard monitoring" and then play through the menus for anything about misfires. Then you likely have to select each cylinder individually and look for a value greater than zero. I'm making it sound harder than it is.

But again, on our '98 I was unsuccessful. I do have one more personality key for my MT2500 to try, and I just picked up an old Modis that will almost surely do it (it was able to pull ABS codes on our '02 CTD, which is another example of data that is there but difficult to access)

 

The info has been there since 96, and OBDII.... The problem I am having, is find a scanner that will even talk to a truck this old.