OK – for those of you who have helped already thank you. Here are the symptoms: Only when warm and coming to a moderate or abrupt stop after at least 45 seconds of continual throttle over 1700 RPMs my truck’s RPMs will dip just below 500 then recover to 650-700 quickly. At one point I could get it to stall. I’ve gotten part way into getting this fixed but need some minds better than my own to get the rest of the way. This is what has been done.

First we hooked it up to a monitor and drove it. We disconnected the ICP sensor and the truck would not do the RPM dip – so we pulled the ICP and it had some oil in it – we replaced it. Still no change.

We changed the oil, it was due and I had some Schaeffers to replace the Rotella semi-syn in there – this made everything MUCH smoother – the oil coming out only had 3k on it but smelled a little burnt. The truck seemed better in all areas, but the dip still occurred.

I had a spare IPR valve and since we were in there we changed it. This is where it gets interesting. When we cranked the truck after putting in the new IPR it bark started VERY quickly. We thought maybe that was it, drove it – the truck is now very smooth and throttle responsive but the dip remains.

BTW – the HPOP build pressure with no hesitation or problems. The cylinder contribution tests look good # 8 is slightly off.

Here are my questions: We think it is a high pressure oil leak - net steps are to pull the valve covers and check the injector seals. I’ve also read something about the oil cooler valves sticking. This seems logical, but I can’t help think it might be electrical. Here’s why – it ONLY occurs once the torque converter releases. What is the signal from the tranny to the PCM that the torque converter has released?

There are several folks on the forum right now dealing with similar symptoms – no two are quite the same. So tell me what you think. Thanks. J-

 

I would think if you have a high pressure oil leak, you also would be getting a hard start issue, especially when cold.

 

Ok - why a hard start when it is cold? (forgive my ignorance) BTW - it was about 28 degrees here this morning and the truck is not plugged in and it starts up fast and strong.

 

Because a high pressure oil leak will slowly leak-down the reservoir overnight, resulting in a hard start the next morning. Without enough oil the the reservoir, it takes longer cranks to get it started, because the reservoir has to be refilled first.

My truck currently has a very badly leaking injector o-ring, and it starts very hard after it has sat for a few hours. In addition, it doesn't do the RPM dip when coming to a stop. It just uses up a ton of oil and spits it into the fuel tank.

Personally I still think you have a torque converter that's going bad.

 

Curtis - I just got off the phone with Jody at DP - he has the same thing with his Ex but he said it has never stalled. We talked a for a few minutes and I'm thinking you could be onto something. So, I'm going to drain and flush the tranny fluid for sure - see if I observe any change. What's the best option for tranny fluid? What is the recommended change interval for lighter duty use?

Also - how can I test/isolate the tq converter?

I've never had my tranny very hot and I tow only about 5000 pounds -

 

correction - no flush just drain per recs on this site for a tranny with my mileage

 

I really doubt that it is a failing torque converter. Possible, but unlikely.

I do think the torque converter is drifting into lockup. The causes of that can be low fluid, a loose or missing internal filter, worn seals, or a worn pump. Really old ATF might be a cause. As ATF is used the viscosity drops. It could be getting thin enough that it's leaking past the seals.

 

Mark,

You seem to be suggesting that the converter locks as a result of a LACK of pressure. Is that correct?

If so, how does the converter act upon initial startup, with no pressure yet built?

Confused....

Pop

 

Mark - thanks for lending your knowledge. I will do a fluid change and see how it impacts the situation and report back.

 

OK - I don't believe it is the torque converter. I tried revving to 2000 RPMs while in park and then dropped my foot off of the accelerator and got the RPMs to dip. Can anyone tell me about oil jets used to cool the pistons?

 

Yes, that's correct. It uses pressure to hold the clutch in the disengaged position. It uses pressure on the other side of the piston when applying the clutch.

It can be dragging quite a bit on startup. But since the trans is in park on neutral, what difference does it make?

 

Does it do this in stock tune? Try it and let us know. Mine does the same thing with any of the DP Tunes, although I've never been close to stalling. My tunes have a downshift feature and when stopping it downshifts in to 3rd and the t/c seems to stay locked longer and drags the engine down to about 600 rpm or so, then it unlocks and idles. The stock setting doesn't do this, but I can tell it's not using any engine braking either.

 

Ok - I have some new info. Keith - It occurs equally in all tunes including stock. Here's the new info - while in park with the engine fully warm, when I change my DP Tuner from 80E or 60T to the stock setting I can get it to stall. I get no lights, and it starts right back up no problem. I can start it in any setting as well. When I am idling in park in stock tune and I move it to 80E or 60T I get a small jump in RPMs and then it settles out very quickly.

 

Are you getting any diagnostic codes? If not it could be a fueling problem. I would try to monitor fuel pressure under load. Also, just a suggestion instead of opening a new thread for a different question just put it in this one. You will probably get more help that way.

 

No codes. I am looking into the fueling issue today - have some avenues to try. re: your suggestion - I appreciate that and I agree in theory, but in practice I've noticed that when a thread dies it is because folks don't have anything to add or may be bored with it and it is helpful to parse out smaller pieces to keep information flowing. That said - ALL the help and information I have ever gotten on this forum is hugely appreciated.