So much bad info in this thread! This is going to be fun. Hang on.

Whether or not the torque converter clutch disengaged the engine wouldn't go to idle. This is NOT a torque converter problem.

Yes they shut off when coasting. No that won't make the tach go to zero.

Exactly.

You're in the wrong column. Sorry.

It *IS* a transmission problem. More on that later.

The injectors WILL shut down if the coast clutch is on and maintaining engine braking. But the coast clutch isn't doing it's job.

Your interpretation was spot on. People are giving you bad info.

The original problem here is that the coast clutch is not engaged when it should be. The engine speed will stay up regardless of whether or not the torque converter clutch is engaged.

When you use the OD OFF button to turn off the OD, the coast clutch is applied by the coast clutch solenoid. If the solenoid is bad or the coast clutch is bad, you'll get the same results - the engine will go to idle speed when you press the button.

If you move the shifter to the 2 position the coast clutch is now applied by a hydraulic circuit. It doesn't matter if the coast clutch solenoid works or not. At 40+ MPH what does yours do when you move the shifter to 2? That will tell me if the coast clutch or the coast clutch solenoid is your problem.

 

Several people in different directions at the same time, which was very confusing. But I think that the OP could have described the problem better and that's really where the confusion started.

Well that helped me at least. I now know my coast clutch is bad because mine drops to idle even in 2nd gear when I let off the throttle going downhill.

He said that when coasting downhill above 45 with no throttle, his engine speed drops to 700 RPM. Is that supposed to happen? I understood that to indicate a problem with the coast clutch.

 

This is not exclusive to CA trucks. Putting the transmission aside for a moment... when the load on the engine is "negative", that means the engine is being pushed or pulled as opposed to the engine doing the work. When this happens, the PCM stops firing the injectors and you should see a Fuel Injector Pulse Width of 0.6 milliseconds or 600 microseconds. That quiet you hear is what the motor alone sounds like - and the noise when you're pulling is the injectors firing. HEUI injectors are noisy buggers, aren't they.

Coast clutch and torque converter... I always get those two crossed up. Thanks for the correction Mark!

As a regular user of compression braking on an HD4R100 transmission, the coast clutch is a very big part of my daily driving. I focus on the TC slip when my engine braking is in use, so I have equated the engine grabbing the drive shaft on decel with the torque converter... completely overlooking the coast clutch.

When in Drive, there is a narrow range between about 30 MPH and 45 MPH where the coast clutch and the torque converter may or may not be working, depending on the situation and tuning. Using my memory, stock tunes drop out the coast clutch somewhere around 42-45 MPH, so the truck will drop to idle (700 RPM) when your foot is off the throttle, and the transmission will "grab" again when you step on the fuel. If the coast clutch were to engage/disengage (I get confused here) below 45 MPH, the drive would feel like a truck with a manual transmission - the engine slowing your momentum until the gear ratio and speed drops the RPM to near idle. In essence, the automatic transmission "pushes in the clutch" to coast every time you let off the fuel below 45 MPH.

 

Yea, this one went sideways faster than I thought it would...

 

Automatic transmissions are confusing to many (well... they are to me). There is a whole lot of if-then going on in that mechanical black box. With the diesel... add fuel, turn it, and watch it go. Transmission is put it in D and maybe the TC will slip or not, maybe the coast clutch will grab or not, and maybe that's a good thing or not.

 

I'm with you on this, Rich, and am certainly in the same boat as you (figuratively speaking). Adding to the confusion is, in my own case, a lack of fluent knowledge of what to call the various events as they take place ("going to idle", etc.). It's so easy to proliferate "bad information" just by way of calling events the wrong things. Along these lines, I'm always so glad to see Mark pitching in with educational information.

 

This thread reminds of me of that progressive commercial where everything is misheard because they're on motorcycles.

"That girl's awesome!"

"I don't see a possum anywhere"

 

I understand automatic transmissions less than I understand women...

 

No, it doesn't work like that at all.

The coast clutch is not engaged when the OD OFF button is not pushed and the OD OFF light is not illuminated. When you press the button and the OD OFF light is on, then the coast clutch is on, regardless of vehicle speed. The PCM does not turn it on and off at different speeds.

If you drive with the OD OFF light illuminated the coast clutch is always on and there is always engine braking. The torque converter clutch can be engaged or disengaged, there is still engine braking.

When the coast clutch is engaged, there is engine braking in gears 1, 2, and 3. The coast clutch cannot ever be engaged in fourth gear. Very bad things would happen. Fourth gear always has engine braking without the coast clutch. When the coast clutch is not engaged, there is only engine braking in fourth gear. With the OD OFF light not illuminated the coast clutch is never engaged.

There is nothing on this earth that I understand less than I understand women.

 

For the love of.... Now I need a graph, with lines showing what's on and what's off... and when. Maybe I can build one with the description above.

I understand women... and we're all doomed.

 

That's exactly what my truck does. It only engine brakes above 42 or 43 MPH. At any other speed, regardless of what I do with the gear selector or OD button, it just idles and I get zero braking. Going down hills with the RV where I can't maintain that speed is scary.

 

Your coast clutch has failed. The trans needs to come out and get torn down to fix this.

It engine brakes above 42 MPH because it is in fourth gear and fourth gear has engine braking without the coast clutch.

 

Hey Mark, do you have this operation chart for the 6R100?

 

I am now at a point where I have to dance around divulging too much here. I have custom tuning that utilizes engine braking, and so many things are going on here are foreign to me.

I can say this - my stock program has always allowed Torque Converter slip below 42 MPH. Maybe I'm really screwing up the nomenclature or describing the transmission behavior all wrong - so I'll just stick with TC slip (since I monitor it so closely). The only time I ever get 100% TC slip is when I am stopped with the transmission in gear. As long as I am rolling or in neutral, I get varying degrees of TC slip and/or a different feel of acceleration/deceleration from the engine pulling or being "pushed". There is no mistaking when the TC is locked whether it's in 3rd gear or 4th, because the RPMs lock in sync with the speed, and the TC Slip gauge reads about zero. I can also feel/hear a locked TC, because of how the truck responds to the throttle - it loses all it's "squishiness".

 

No, I don't.