RPMs

[98BlazerLT]

Sometimes if I am going around 45 mph and the transmission goes into OD, about every 5 seconds my rpms will rise anywhere from 50 to 300 even though I am applying no extra pressure to the throttle and the speedometer also stays the same. To make sure I wasn't causing it I tested it with cruise control on and it still did it. I feel it hesitate a little bit right before the rmps move like it is going to go out of OD. It will also do it going about 35 or 40 mph in 3rd gear but in 3rd gear the jump is only about 50 to 100 rpms and it jumps more frequently, about every 2 seconds. I had the fuel filter replaced but stopped at that since the mechanics didn't know what it was and it could have cost me thousands before they figured it out. Any ideas?

[DINO55]

How many miles on your truck, And when was the last time your transmission was serviced, (Fluid exchanged and new filter installed)

[BlazerLT]

Sounds like the torque convertor is having problems locking up.

Any check engine lights?

[534BC]

Touching brake pedal will cause unlock, letting off throttle or pushing throttle will cause unlock however you said that you were keeping pedal steady so I would try to increase speed 2 mph , it may be right at the minimum speed or minimum tps value required for lock-up. Mine is exactly 41 mph and will stay locked only if the road is very smooth and not hilly (my minimum for 3rd gear is also 41 mph) I wish it was adjustable, doh.

It may be acting normal?

[BlazerLT]

Originally Posted by 534BC

Touching brake pedal will cause unlock, letting off throttle or pushing throttle will cause unlock however you said that you were keeping pedal steady so I would try to increase speed 2 mph , it may be right at the minimum speed or minimum tps value required for lock-up. Mine is exactly 41 mph and will stay locked only if the road is very smooth and not hilly (my minimum for 3rd gear is also 41 mph) I wish it was adjustable, doh.

It may be acting normal?

True, it might be fluttering around the torque convertor lockup speed.

Go above that speed and it should stay in lockup unless you release the gas or touch the brakes.

[vis_inc]

Have you tried a throttle position sensor. I have the same problem with my 96 blazer. I had a very similar almost exact same issue with my 99 Durango and it fixed the problem just not sure if it is very common with the blazers?

If I were to guess I would steer towards the throttle position sensor rather than the torque converter. Mainly since the throttle position sensor is only $30 and how much is the torque converter going to cost you? Much more $$$

Let me know if you have figured out the problem.

I am probably going to just try the throttle position sensor.

[534BC]

Originally Posted by 534BC

Touching brake pedal will cause unlock, letting off throttle or pushing throttle will cause unlock however you said that you were keeping pedal steady so I would try to increase speed 2 mph , it may be right at the minimum speed or minimum tps value required for lock-up. Mine is exactly 41 mph and will stay locked only if the road is very smooth and not hilly (my minimum for 3rd gear is also 41 mph) I wish it was adjustable, doh.

It may be acting normal?

Sorry, I said tps and after driving it I think it is using map sensor. No matter though. It seems that any value above idle position will lock up converter as long as all the other variables are satified.

[534BC]

I think that LT may agree (is it a first?) that even though the convertor is locking and unlocking we are not saying it is the convertor that is bad. It is symptom and the convertor is just doing what it's told.

[BlazerLT]

Originally Posted by 534BC

I think that LT may agree (is it a first?) that even though the convertor is locking and unlocking we are not saying it is the convertor that is bad. It is symptom and the convertor is just doing what it's told.

Very true, around that speed you will have the torque convertor locking and unlocking.

I don't think there is anything wrong with his truck at all. It is running properly.