I have a 2002 Ram 2500 with a 5.9 gas engine that is giving me an issue that I cannot seem to figure out. Hoping that some of you will have some input. It all started after a transmission removal / rebuild / reinstallation, but I cannot figure out why:

The engine will run very rough / erratically. The tachometer seems to bounce up and down, despite what the engine is doing. There are times where it all smooths out for a few minutes, but then it is back to running like it is only running on 3 or 4 cylinders. It has no power and is not driveable. Prior to pulling the transmission, it ran fine, and had great power.

I suspect it may be the intake plenum, but cannot see any oil or contaminants when looking down inside the throttle body. The truck does burn oil, however, maybe 2 quarts between changes, it is a plow truck.

So far, I have done the following:

Tune up with new plugs, wires, cap, rotor, crank sensor, cam sensor, and throttle positions sensor, idle air control valve. No dice.

My fuel pressure is 50 psi at idle. Cannot get it to rev predictably, but fuel pressure remained high. It is a new airtex pump.

Vacuum at idle is in the 20 inches range, and the gauge is steady. If I open the throttle, the engine does speed up and choke / sputter, and the vaccum drops to almost zero. The other night, with the vacuum gauge on it, the engine suddenly decided to fast idle at 2500 rpm, very smooth, no chugging / choking, and the reading was steady at around 20 inches. Then it just decided to slow down, and start running erratically.

Even when it was fast idling, the tachometer would bounce unpredictably.

When I pulled the plugs, the #8 (rear most, passenger side) plug had oil on it. The only one that did.

If I drive it up my driveway, it spark knocks like mad. It can putter around the yard but that is it.

Though maybe I had damaged the catalytic / had an exhaust obstruction, removed first the muffler and then the Y-pipe the other day, and started it briefly in both conditions. Besides being loud, no change in how it ran (bad idle, rough, no power).

I have reset the computer, and replaced the cam / crank sensors as a result of error codes. There was also an evap system error code that I set when I pulled the vacuum line off to set my gauge. No other codes.


Any input would be appreciated. This has been a very good running engine. Looking back on last winter when I was plowing with it, I can recall that it never really went into a fast idle setting properly when it was cold out (all winter here in maine), and it would run a bit erratically when cold, but then it would smooth out as the engine warmed up, so I am thinking this issue may have been there in a very mild form prior to pulling the transmission.

Local shop want $500 to do the plenum gasket. I will not hesitate to make this repair on my own, but would like to know what you all think first.


Thank you in advance!!!

 

Sounds like a clogged cat. Remove the front O2 sensor and see if it doesn't run better. Don't just unplug it, physically remove it.

 

Thanks. I considered that, and actually removed the muffler section, and then the entire y-pipe, thinking it was an exhaust blockage. The engine actually ran exactly the same, just really loud. The jumping tachometer, rough running, all of that was the same.

 

Take a look at your crank sensor. They are frequently victims of engine or trans R&R.

 

Thank you. I have had two different (new) crank sensors installed, no change in how this engine runs.

 

What brand sensor? Our engines don't particularly care for some of the lower cost aftermarket sensors......

How many miles on the truck?

The plenum can give some of your symptoms, but, it would have to be REALLY bad to make the engine run like that. Given 20" of vacuum at idle, that is steady, I don't think the plenum is the problem.

Have you checked for wiring pinched between the engine and trans?

 

I have had a borg warner crank sensor and also a standard motor products unit. neither unit was from china. after replacement, the code for this went away, but the code for the cam postion (pick up) sensor remains. I have ordered one of those from Chrysler. Next is to check the wiring, as you indicate. thank you.

 

Let us know what ya find. Gotta be something relatively simple.

 

Similar issue to yours, I just replaced my 5.9 engine. Used only the block, heads and distributor from new engine as mine was a 95(auto) and the new one was a 97(manual) and all the sensor plugs were different, used original cam sensor, cap and wires. The old engine was burning oil, poor compression and sucking past the valves but ran surprising well with clean plugs, totally drive-able but burning a lot of oil. After swapping the plenum(new base gask), exhaust manifolds, etc etc and re installing the engine it is drive-able when first started but as soon as it comes up to running temperature it coughs and sputters and is not movable. It sputters a bit when cold but pulls fairly hard on acceleration. The computer is not throwing any codes. In an attempt to fix I have installed a new cam sensor, IAC, MAP, TPS, coolant temp sensor and new injectors. 40psi fuel pressure. Runs "ok"(drive-able but not great) till the thermostat opens and then starts to pop and fart and barely run. No codes present. Timing marks are about 5 degree before TDC, Vacuum is a little low but not terrible. Crank sensor on old engine was broken when old engine was removed so new one was installed. Everything was transferred from old engine to new other than new NGK spark plugs and the crank sensor. Does anyone or has anyone experienced a failure of crank sensor that resembles this poor running condition after engine warms up? I did see the new engine run before I bought it and it was smooth running and strong. Perplexed....

 

Disconnect the O2 sensor, and see if that doesn't improve its attitude.