Hello. Gotta get my TCC to lock up, because I get 18mpg with very conservative highway driving. Here's some background.

The car is an 87 GTA with an 89 L98/700r4/ECM(from a Formula350). Everything is stock except for BoschIII injectors and a Superchip PROM.

What I'd really like to know is what color and location are the wires that control the TCC from the C207, C100, etc. A wiring diagram would be awesome. The diagrams from austinthirdgen.org are from a Camaro and they are totally different from a Firebird.

I have a few wires coming from the C100 that were cut when I spliced in the new harness. I'm sure one of those is for the TCC, but I can't tell which one.

Please help.

 

ECM controls the TCC lockup - so the wiring between the Camaro and the Firebird will be identical. The only wiring differences between the 2 cars are cosmetic wiring for things like lights, maybe guages, etc. The ECM wiring, sensor wiring, tranny wiring are identical. Pontiac has not made any of their own engine/tranny stuff since the mid-1970's - it's all Chevy internals. None of the TCC wiring should be in the C100 connector - that's all basic lights and basic function wiring that has nothing to do with ECM or sensors.

There is a sticky in the carb forum that discusses the wiring for the TCC lockup and how it functions. And the wiring diags from Austin will be correct for your Pontiac.

Are you sure it's not locking? MPG is not a good way to tell - I know several folks with TPI 350 stock setups and fresh tune ups that are not even getting 18 on the highway. The 350 TPI cars never got as good of mileage as the 305 cars did. While gently accellerating, count the shifts, and look for the tach to drop very slightly after the shift to 4th - it only drops maybe 200 - 500rpms and it's barely noticeable, but you should be able to see it on the tach.

 

Hey, thanks for replying. I will use the Austin diagrams to go shoot my wires then. I thought there was a C100 wire for the TCC. Thank you for clearing that up! I am absolutely positive that it isn't locking up. I count 4 shifts, and no lock up. I'll try to go out to the car now and shoot some wires. I'll report back soon. Thanks again.

 

Failure of lockup shouldn't affect mileage that much. Your non-lockup could be a secondary affect of the actual problem. Verify that the ECM is commanding lockup with a test light at the ALDL. Troubleshooting info is in here:

https://www.thirdgen.org/forums/tran...-4th-gear.html

You may find that something as simple as your CTS is bad/open and your vehicle is not going into Closed Loop.

 

A few things have to happen for the T/C to lock up, 1st, engine has to be up to temp, 2nd, will not lock up until speeds above 30-40mph, and it won't lock up until 3rd or 4th gear. The trans also looks at engine load (using the TV cable). Don;t forget to check the TCC fuse and all other related fuses. Verify all other systems are functioning properly first. IF everything seems ok, try pulling the pan and checking the resistance across the T/C solenoid. Should be 21-33 ohms. if its higher you've got a "open" in the solenoid windings, if it's less, you've got a shorted winding. If the sloenoid is ok, looks like either a problem with the wiring to the solenoid/ECM or a hydraulic circuit problem inside the trans (very unlikely). Hope that helps you out. Good luck!

 

Thanks for the help, guys.

First of all, I want to report on what I found today. I verified the signals at the 4-prong connector on the trans. and the continuity fromA7 (tan/blk) at the ECm and pin F on the ALDL.

With key on, engine off:
All 3 wires on the 4-prong have 12VDC.

While the car driving down the road at anything below 40mph, the tan/blk wire shows 12VDC. Shortly after the car hits 4th gear, the readings on the meter go berzerk. Sometimes it reads OL, others it read between 10VDC and 8 VDC. Nothing consistent. As soon as I let off the throttle, it goes back to showing 12VDC. Doesn't that mean that the ECM is commanding the lock-up?

What kind of signal should I get at pin F on the ALDL? Are the signals at the 4-pin correct? I don't think so, so I'm going to look at the link posted above. All of the fuzes are good, and the car runs great. I know I can't determine if the car is going into closed loop without tuning software or a scanner, but I assume it is. The CTS, TPS, IAC, O2 are all new and adjusted and functioning properly as far as I can tell.

Any thoughts about this stuff?

 

By the way, the transmission has 15,000 miles on it after a rebuild. I'm not sure what was replaced, or refurbed, but the work was worth $2100 at a reputable shop.

 

I can't remember the voltage at each pin, but there is another post on here that shows all the different wiring colors by year and I think voltage at each pin was in there. Should be able to search under "converter" under the transmission section in an advanced search for titles only - the post I am talking about will have a lot of hits.

My issue ended up being the switch on the brake pedal. It was out of place and the dip switch was always out which basically was telling the trans my brake was always on and the lock up would not happen.

If you remove the hush panel you will see two switches against the brake pedal. One is the brake light and the other was the TCC/vacuum/brake switch. On my 83 model the TCC was white.

Moved the switch in the mount into the correct place and it locked up on the first drive after that.

Might be an issue for you and a real easy fix. At least take a look at the thread I mentioned and/or take a quick look at your brake switch.

It should pay dividends.

 

Thanks. I think I remember looking at that thread. Trickster had a lot of good input into that one.

My brake switches are both good.

I will check out that thread.

 

Some good information on this thread.

https://www.thirdgen.org/forums/carb...c-control.html

I guess my next step is the determine which TCC system I have. One with a normally open or closed 4th gear switch. Then I can determine if my power signals are right at the 4-prong. Then I should be able to tell if my TCC solenoid is good or bad.

 

That is the thread I was referring. It is very helpful.

Good luck!

 

If you figure out what the problem is let me know, I also have a 87 gta with a converter that won't lock up. I have replaced my TCC solenoid, solenoid connector, brake pedal switch, and temp sensor, still no lock up. I'm thinking something may be wrong with the converter itself.