Convertor locks and unlocks

**Chevellessjeff** · 10-30-2006, 10:08 PM

Okay... I'm new.. anyway. I have a 99 z28 that locks and unlocks the convertor when driving around town. Sometimes it will do it on the highway at part throttle. I have had the trans rebuilt by a reputable shop and the convertor has been replaced. When I get to about 30-35 the trans shifts to fourth and then starts locking and unlocking the convertor. It does have a ses which says the cats are bad. I believe they are hollowed out. Will the cats being clogged cause this locking and unlocking? I have been told yes and no. Should I take it back to the tranny shop? I have also heard a misfire can cause this problem too.

Someone help me please.

**2001NBMZ28** · 10-31-2006, 05:09 PM

What TC? Depending on the throttle position/braking around town it'll lock/unlock. Not an expert but mine locks at part (steady) throttle around 40 MPH after the temp gauge reads 1/4 (like 140 on my scanner if I remember correctly). If the cats are gutted and codes are only for the rear 02's' shouldn't be the problem, if not and they're clogged don't know. A misfire can cause the TC to unlock. I'd double check the codes and determine if the cats have been gutted. Also if someone gutted the cats I'd think they would've either turned off the rear codes or put 02 sims on? Like I said, not an expert...hope this helps - TTT for you.

**nhraformula** · 10-31-2006, 06:45 PM

bump up the mph to lock up at 45.
driving around town where speed limits are 35 and youre doing 33-37 mph ,youre car will search for a gear, mine did that for awhile untill the tuner bumped up the mph.

**Chevellessjeff** · 10-31-2006, 06:52 PM

Umm.. it's a stock tc. It's only at part throttle from 30-35ish to around 45-50ish. I don't have a tuner but if I did I was told to set the tc to only lock in 4th at or above 50. When it's hot outside it does it worse. In fact in the summer I have to drive in 3rd. My plans are to put headers on, take out the cats, and delete the back o2's. I believe the person who originally modded this car was ignorant. I just want to make sure that I am not missing something before I go and drop more money on this.

The funny thing is.. before the tranny was rebuilt while it was slipping the car still ran 13.6 @104 in august 100 degree weather. I'm hoping when it's fixed it will run even better.

Thanks for the help guys. It sounds like I'm going to have to order a tuner.