Rpm Question Crusing 70 Mph

[boomer62]

I Have A 1999 Blazer 4wd, Automatic. About Once A Week When On The Thruway At 70 Mph, The Rpm Reads 2400. Normaly It Is At 2000. It Can Run Normal Rpm When I First Get On The Thruway And After The Tolls It Will Read 2400 Rpm Till I Get Off Or Within 5 Miles It Will Drop Back To 2000 Rpm. Other Times It Will Not Drop At All Till I Get Off. If I Drop It Down To 3 At 2000 Or 2400 Rpm It Reads 3000 Rpm For Both. Does Anybody Know What Is Causing This Problem ?

[97cavalier]

Originally Posted by boomer62

I Have A 1999 Blazer 4wd, Automatic. About Once A Week When On The Thruway At 70 Mph, The Rpm Reads 2400. Normaly It Is At 2000. It Can Run Normal Rpm When I First Get On The Thruway And After The Tolls It Will Read 2400 Rpm Till I Get Off Or Within 5 Miles It Will Drop Back To 2000 Rpm. Other Times It Will Not Drop At All Till I Get Off. If I Drop It Down To 3 At 2000 Or 2400 Rpm It Reads 3000 Rpm For Both. Does Anybody Know What Is Causing This Problem ?

It is just probly the way your tranny is shifting. Or you may be on the gas a little more than normal, or pulling a little heavy load.

[boomer62]

Same Route To And From Work. It Does It Even With The Cruse On.

[herkyhawki]

The Torque converter is locking and unlocking. Don't worry about it. It could even be difference of headwind vs. tailwind.

[DINO55]

Slight incline in the roads could be downshifting the transmision. Just a thought...

[boomer62]

Drove this route for 7 years, only time i got the rpm to change that much when i had high winds or snow, and i would feel the down shift. this never happen all this years till about 5 weeks ago, this happens on level dry road and no wind.

[blazee]

Originally Posted by herkyhawki

The Torque converter is locking and unlocking. Don't worry about it. It could even be difference of headwind vs. tailwind.

I agree, sounds like the torque convertor locking and unlocking. Next time you are driving:

When it is at 2,000 RPMs, hold the speed constant, and gently mash the brake pedal. (just enough to turn on the brake lights, not hard enough to actually apply the brakes.) If it is the torque convertor, the RPMs will jump to 2,400.

When it is at 2,400 RPMs repeat the above procedure, If it is the torque convertor, in this case the RPMs should remain constant when the pedal is pressed.

[boomer62]

Originally Posted by blazee

I agree, sounds like the torque convertor locking and unlocking. Next time you are driving:

When it is at 2,000 RPMs, hold the speed constant, and gently mash the brake pedal. (just enough to turn on the brake lights, not hard enough to actually apply the brakes.) If it is the torque convertor, the RPMs will jump to 2,400.

When it is at 2,400 RPMs repeat the above procedure, If it is the torque convertor, in this case the RPMs should remain constant when the pedal is pressed.

I did the brake pedal at 2000 rpm and jumped to 2400. At 2400 it remain the same. Is it the torque that is bad or icould it be a bad sensor, module or switch for the torque converter causing the problem?