Normal RPM?
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Laughing Gas
Joined: Nov 2003
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Normal RPM?
I have noticed something weird. If flooring the gas at 33+ mph, the point where it drops into 2nd gear the truck will accelerate hard turning close to 3k rpms and climbing, but after accel. hard in 2nd gear for a few seconds the rpms drop about 300 and then keep on accelerating. Is this normal? It is not a trans slip or anything like that. I used to have a 99 ranger that did that exact same thing. Any advice would be great.
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Laughing Gas
Joined: Nov 2003
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Correct there is no gear change. Say if im cruisin at 32 mph, then floor the gas, the truck will go into 2nd gear and start accelerating. Somewhere around 3k rpm in 2nd gear the rpms will drop about 200-300 and then continue accelerating, it is smooth, its not some hard hit or anything the engine doesnt choke down. Any ideas?
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Laughing Gas
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From: Louisville,Ky.
HMMM, not quite sure then. possibly a dirty MAF or fuel filter, causing a momentary lean condition?
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From: SW VA
Originally Posted by Joe Finn
ATC,
I thought he was describing a 300 rpm drop without a gear change.
I thought he was describing a 300 rpm drop without a gear change.
It's might be the TC locking up....although now that I think about it....my truck doesnt drop RPM's like that. It just keeps on climbing.
Postmaster
Joined: Aug 2001
Posts: 4,532
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From: Trussville, Alabama
From what I have seen, the torque converter locking up will drop rpms by about 300.
Sounds like that's what is happening.
Not sure if it is supposed to be happening under the circumstances you describe, but it sounds like that's what it is.
Sounds like that's what is happening.
Not sure if it is supposed to be happening under the circumstances you describe, but it sounds like that's what it is.
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Laughing Gas
Joined: Nov 2003
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Its not anything bad... well if it was a race truck itd suck, but i mean the engines not stalling out, the truck keeps on accelerating when it happens, u can barely feel, u see it on the tack, and hear it more than anything, what happens when the TC "locks up"?
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Laughing Gas
Joined: Nov 2003
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I thought (I dont know much about it) that the TC locked up in OverDrive. When does it lock up and what funtion does that serve. All I really know about it is that it forces tranny fluid outside...?
Postmaster
Joined: Aug 2001
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From: Trussville, Alabama
The torque converter is a fluid coupled device. It uses fluid forces to create movement of the auto.
The fluid coupling allows for the benefit of torque multiplication, and also you can stop at a red light and hold the vehicle still while the engine stays running and connected to the transmission.
These are a result of the fluid coupling allowing "slip".
BUT, this "slip" if you will, also means wasted energy and therefore lower MPG.
The fix? When things are right (as determined by the designers/engineers) clutches in the torque converter "lock up" so there is no slip, in essence the TC is out of the picture, and you get a little better mpg.
Need to accelerate?
Press on the gas, TC unlocks, RPMS jump just a little (because now the engine is free to spin faster than the transmission because of the fluid "slip")
You accelerate on your way, and when things get "right" again, the TC will lock again.
In some ways, the TC is like a manual clutch.
Ever "slip the clutch" when starting out with a heavy load?
You run the engine RPMs up and slip the clutch to get the load moving, then when all is right, you let the clutch pedal out and the clutch/pressure plate/ transmission now "lock up".
The fluid coupling allows for the benefit of torque multiplication, and also you can stop at a red light and hold the vehicle still while the engine stays running and connected to the transmission.
These are a result of the fluid coupling allowing "slip".
BUT, this "slip" if you will, also means wasted energy and therefore lower MPG.
The fix? When things are right (as determined by the designers/engineers) clutches in the torque converter "lock up" so there is no slip, in essence the TC is out of the picture, and you get a little better mpg.
Need to accelerate?
Press on the gas, TC unlocks, RPMS jump just a little (because now the engine is free to spin faster than the transmission because of the fluid "slip")
You accelerate on your way, and when things get "right" again, the TC will lock again.
In some ways, the TC is like a manual clutch.
Ever "slip the clutch" when starting out with a heavy load?
You run the engine RPMs up and slip the clutch to get the load moving, then when all is right, you let the clutch pedal out and the clutch/pressure plate/ transmission now "lock up".
Last edited by BrianA; Apr 17, 2006 at 01:26 PM.