Hello all,

This is my second post and hope this is in the right section this time

I have a 98 Ram 1500 4x4 5.9 vin Z. She got a new engine and rebuilt trans 15K miles ago with all new sensors etc.

The engine rebuild was new long block and top/bottom dress with all new sensors. The old engine had 182k on it and still ran fine with exception of leaky head gasket. I figured if it was going to be torn down that far and with 182k, just swap the whole motor. The new engine has 15K miles on it and runs like new.....except after warm up of late.

Recently (400 miles ago) I started noticing that the trans would thump....as if torque conv lock up was unlatching/relatching under load at about 40-50 mph, At 60-70 mph seemed ok. My quick fix was to turn OD off under 60 mph and seemed ok.,,,or at least didn't notice it. It's gotten worse now...especially in the last 200 miles where the thumping has increased...at any speed over 40 with or without OD engaged. With foot off the gas lock-up disengages and no issues.....as soon as I press on the gas, thumping/banging.

Another clue is that when the truck is cold it all works perfectly....then starts acting up after say 5 minutes of running/driving and up to operating temp. The warmer it gets, the worse it gets to now its almost crazy to drove over 40 mph with the banging. The trans otherwise seemes to shift fine through all gears. It only acts up when I hit 38-40 and the TC goes into lockup.

The latest symptom is after the same warm up period, the engine is starting to miss and even hear a few pops under load. Again when it's cold, all works as it should.

I replaced the throttle position sensor and no change. The post cat O2 sensor is new a month ago (was shorting and dropping my 5 volts out and causing eratic shifts) and I just replaced the pre-cat o2 sensor today and no change.

I checked PCM ground and harnesses for chaffing etc, and all lookgood.
No check engine light of any codes on the OBD scanner. At this point, and being the PCM thinks all is ok, I'm suspecting a possible problem with the PCM ?? I had my attention on possible pressure sensor or solenoid in trans until the missing/poping problem showed up and comes and goes with the lockup thumping when cold/warm. The problem at this point is consistant....no issues when cold, and missing and trans thumping when warm.

I'd prefer the rear blew up and spit the gears all over thr road...that I can fix! The mystery problems are crazy. Any ideas would be apreciated. Thanks!

Mike

 

Has the plenum been repaired? Your initial symptoms are all the signs of a failing O2 sensor, which I see you have replaced. Did you reset the PCM after doing so?

The thumping/banging at around 40 mph is a pretty good indication of a miss. If the O2 sensor/PCM reset doesn't take care of that, you need to start looking deeper. Pull a couple plugs, especially those in the back.... 7 and 8, and see what they look like. If they are ash-fouled, you prolly have a blown plenum sucking oil and fouling plugs. Right around 40 MPH, TCC locks, and any misfiring cylinder will make it's presence known..... it kinda feels like the truck is trying to shake itself apart.

 

Thanks for reply! Yes plenum pan was all new and re-sealed when engine was built and I'm not losing a drop of oil at this point. I'll take the breather off and look inside just to make sure.

No the PCM was not reset......is there a specific procedure? I honestly didn't know it needed a reset. Does it require a reset for faulty o2 sensor symptoms to go away?

 

Does it have the original cat?


Edit: Anytime anything is done with any sensor or anything electrical for that matter. The negative battery cable should be removed before doing any work. This will also reset the PCM.

 

Thanks, will reset the PCM and see how it goes. The CAT was gutted about 80k miles ago. Learned a trick from mechanic to use a spark plug antifoul extention to pull the post cat sensor from the main exhaust stream so it still sees the heat and a bit of exhaust and she's been happy ever since. I'll report back what I find.

 

That takes care of any clogged cat issue. And I'm still curious as to what brand pre cat sensor you installed. Not Bosch I hope.

 

Yes Bosch....my bad? Ok, good news! preliminary results with the PCM reset are good. Ran 20 minutes and all seems ok. I would have never thought the thumps in TC lockup were misses. Thanks!! Made my day and Merry Christmas!

 

Congrats, now extend that Holiday feeling and order a couple NTK o2 sensors from Rock Auto. And use the code in the thread from the general discussion section.