I have a 1992 Pontiac Firebird convertible that has a 305 tbi with an 700r4 and has 2.73 rear gears and when im in overdrive at about 20-50 mph that car likes to kinda surge like it may have a slight miss or like it wants to down shift but its very slightly feeling when it does it but im still able to get 24 mpg in it.
Any thoughts of what it could be?

 

bump

 

Could be the torque converter locking and unlocking - they call it 'hunting'. Although the TC can lock in 3rd, you might try using D instead of OD and see if it makes any difference - if it seems to, then might just be that - check tranny fluid level - it might 'hunt' if the fluid level is low.

 

FYI, I had an 87 Chevy Silverado that was going in and out of lock up. I discovered when I held the break peddle out with my foot, the tranny would stay in lock up. I had a mechanic friend tell me it was the switch hooked up to the break peddle. When you apply the breaks, the tranny will unlock. Before I knew the problem I thought the tranny was flyin south.

 

Does the tach read steady when it's doing this?

 

No. The tach will show a slight difference. I think it's about a one and a half thousand difference. I'll have to check the revs when it locks up.

 

When my car does it, my RPMs rev up and down about 200-300 rpm until I press on the gas harder then it doesn't do it

 

I think that's what mine reved when It was slipping in and out of lock up. I wrote that message in the middle of the night and half asleep. It sounds like your tranny is going in and out of lock up alright. Try driving and holding the break peddle like I did. It wouldn't hurt to try.

 

Just for the heck of it, try driving and pressing lightly on the brake peddle while driving. This will cause your tranny to unlock, and it will go back into lock up. See if the rpm change is the same as your surging problem. I am going to drive my RS today and I will do the same to see the rpm difference. Let me know what you discover.

 

What do you mean by holding the brake while driving? What causes my tranny to lock in and out?

 

What I mean is, the tranny will go out of lockup when you press down on break. Try it. After the tranny is nice and warm go out and drive it and watch your tach when you break. Do this at about 40 mph in D. Not enough to feel breaking, and see if your revs are the same as the issue you have. When you do this, keep your foot on the gas peddle.

 

Yes mine does that... what causes this?

 

The lockup is just for cruising. When you break or accelerate, it goes out of lockup so the tranny is not under undue strain. Is it the same rpm range as the problem you have been having?

 

yes it surges at aroung 1400-1600 rpm but it does it in 2nd, 3rd, and overdrive.

 

Is the surge the same rpm as the problem?

 

yes

 

Well then it sounds like your torque converter is going in and out of lock up. I was told the 700r4 is not supposed to lock up in 2nd, but mine does. If I cruise in 2nd for a while, it locks up.

As with your issue, probably something simple like the switch the break peddle engages. I wish I knew more about where it is located.

 

The 700R4 with an EFI ECM will lock up in 2nd (and 3rd and 4th). It is only 1st that the 700R4 can not lock up in. The 1st gear no lock up is due to the transmission circuits. No feed to the TCC when in 1st.

The TCC brake pedal switch is at the brake pedal. There is also a cruise control switch if the car is so equipped. The TCC switch is doubled up with the brake light switch. To adjust both switches (CC & BRK/TCC) , just push them forward until the outer plastic piece touches the brake pedal arm.

If need be pull the brake pedal towards the rear of the car and hold it while doing this adjustment.

The TCC lock/unlock can also be caused by a bad connector at the tranny.

RBob.

 

I wanna thank you for the info RBob. I was told by a tranny rebuilder that the r4 didn't lock up in 2nd gear.

 

where on the transmission is the TCC connector, because an Iroc im workin on is locking and unlocking, and the two switches that touch the brake pedal are already makin contact with the pedal

 

Left side, above the pan rail.

RBob.