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.

 

I'm guessing it's the torque converter locking up.

 

If they drop to only 300, then there is something wrong. When I get on it, each gear goes to about 5,000-5,500RPM and then drops back to around 3,000RPM after the shift....

 

ATC,

I thought he was describing a 300 rpm drop without a gear change.

 

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?

 

The stock tach's aren't the most accurate things in the world. It could just be a slow reacting needle.

 

Well you can hear it and feel, and its after the needle has begun to climb.

 

HMMM, not quite sure then. possibly a dirty MAF or fuel filter, causing a momentary lean condition?

 

Ohhh...I was thinking after the shift, the engine dropped down to 300RPM's...

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.

 

My 98 F150 5.4 does the same thing.

Rick

 

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.

 

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"?

 

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...?

 

The TC will lock up in any gear. It will usually lock up when you are light on the throttle...say, just cruising down the road at a steady speed.

 

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".