stupid question
Thread Starter
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More Turbo
Joined: Apr 2009
Posts: 712
Likes: 1
stupid question
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??????????
Butt-Head
Joined: Apr 2004
Posts: 9,413
Likes: 2,901
From: Reed Point, MT
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.
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.
Frmr Ford Trans Engr
Joined: Aug 1999
Posts: 24,700
Likes: 2,620
From: SE Florida
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.
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.
Posting Guru
Joined: Feb 2004
Posts: 1,873
Likes: 1
From: Phx, AZ
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.
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.
Post Fiend
Joined: Jun 2006
Posts: 9,714
Likes: 2
From: White Mnt's,New Hampshire
if he is above 35 MPH -+ the RPM's should not drop to idle..the TC should stay locked....at least mine does...
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More Turbo
Joined: Apr 2009
Posts: 712
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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
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Post Fiend
Joined: Feb 2007
Posts: 14,541
Likes: 2
From: Dallas-Ft. Worth
Depends on tuning, Ron. My TC lock/unlock is set to different speeds depending on which type of tune I'm in.
Post Fiend
Joined: Feb 2007
Posts: 14,541
Likes: 2
From: Dallas-Ft. Worth
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.
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.
Posting Guru
Joined: Feb 2004
Posts: 1,873
Likes: 1
From: Phx, AZ
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
Posting Guru
Joined: Mar 2007
Posts: 1,905
Likes: 2
From: East Peoria, IL
Post Fiend
Joined: Jun 2006
Posts: 9,714
Likes: 2
From: White Mnt's,New Hampshire
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...
Frmr Ford Trans Engr
Joined: Aug 1999
Posts: 24,700
Likes: 2,620
From: SE Florida
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.