Hey guys I work on diesels all day but for a refrigeration company not pickups. I picked my 01 250 7.3 yesterday in PA and drove it home. while driving home I noticed when going down hill or when you let off the throttle the RPMs drop right to idle. But other times the RPMs stop at 1000 the engine stops making any noise then drops to idle and the noises come back. This sounds stupid but I'm just curious if that is normal or could the be related to the CPS??????????

 

Totally normal.

The shift strategies that these trucks have as well as the injector lag time create the characteristics you speak of.

If someone wants more detail, I'll get into it. But for now, no worries.

 

When it drops to idle, your TC isn't locked. When it stays above idle, but the injectors are shut off, the RPMs will be up, but no injector noise. Like Cody said, totally normal.

 

thanks for the info!

 

That's not correct.

When it drops to idle the coast clutch is not on and you're in a gear lower than 4th. It does not matter if the torque converter is locked or not, it can drive the engine either way. It will spin the engine about 10% faster during coast if the converter is locked, but it will spin it either way.

If the torque converter is locked, the trans is in 1,2,or 3, and the engine goes to idle speed it means the coast clutch is not engaged when it should be.

 

Huh thats funny.... My TC LED light turns off exactly when the injectors get loud while coasting. I am going with it's the TC unlocking and tranny has down shifted, as it was previously stated

 

if he is above 35 MPH -+ the RPM's should not drop to idle..the TC should stay locked....at least mine does...

 

the truck is rolling around 35-40 and the rpms either stay at 1k and the injectors stop then the rpms idle and you hear the injectors again or they drop right to idle. The previous owner did install a new rebuilt trans after the original went

 

Depends on tuning, Ron. My TC lock/unlock is set to different speeds depending on which type of tune I'm in.

 

It's interesting that mine drops right when my tuner says the TC unlocks. And in my tow tune, the TC stays locked to about 30mph in 3rd.

 

Tested it last night. Flipped my TC switch and kept it locked up down into 1st gear. 15mph, 1000rpm's unlocked it. Injectors were quiet all the way down till I unlocked it.....so to answer the original posters question. Everything is fine, and yes as you were told the noise u hear is after the TC unlocks the rpms drop down to idle and the injectors are firing. Now worries man u r good

 

I wouldn't mind a little more detail

 

mine with a chip the TC locks at 27 MPH and stays locked on down shifts too..but i didnt see any mod's listed..so i assumed we were talking about a stock truck...

 

Coast Clutch?

 

You can go with that, but you don't know how a transmission works.

I think your trans is shifting from 4 to 3 when the converter unlocks. That's why it drops to idle. What you say just doesn't make sense when you understand the powerflow through the transmission.