P1257

Normal driving should not produce any boost at all. It's easy for me to stay out of boost and still have great around town acceleration. I only get boost when I lean on it, and I definitely don't have to go to WOT to get my 7-8 psi. I can do that at half throttle at low speed.

The 95 transmission would be a 4T60. How hard would it be to disable the TCC electrically?

Don't know. It's a switch/solenoid inside the transmission. I'm going to try the brake tap tomorrow to see if it locks up at the place it normally sets the code. It COULD be that it needs a filter & fluid change. MAYBE, when it's cold, the fluid is not thin enough to get through the filter to lubricate the trans. properly. Could be why it's not an issue when it warms up.

LARRY70GS wrote:

The 95 transmission would be a 4T60.  How hard would it be to disable the TCC electrically?

AFAIK it can only be done with a Tech II scanner. It probably would be easier to temporarily set the brake pedal switch so that its always on somehow. Not sure if thats something that can be done?

th3fr4nchi5e wrote:

LARRY70GS wrote:

The 95 transmission would be a 4T60.  How hard would it be to disable the TCC electrically?

AFAIK it can only be done with a Tech II scanner. It probably would be easier to temporarily set the brake pedal switch so that its always on somehow. Not sure if thats something that can be done?

I wasn't sure OBD1 required that, but the brake switch should be easy.  Just pull it out of it's mounting so that it is always activated. The brake lights will be on regardless of pedal position.

Still stumped. According to my Scanner, no difference between data regarding TCC lockup, whether car hot or cold. TCC is not locking up, which is normal; code only sets when car cold, within 5 minutes of driving it. No code after that, under same conditions. Also changed Trans. fluid & filter; same thing, no difference in Scanner data regarding downshifts, TPS, etc. Code still sets as mentioned above, & doesn't set when car is warmed up under same circumstances.

Terry, you are going to have to think outside the box here. Obviously this is temperature related. What changes with temperature? Mechanically, heat expands things, cold contracts. Electrically, heat causes increased resistance in circuits. Something is changing with the temperature.

Yes, however, temperature is not a factor as long as I downshift & keep RPMs around 3000, when vacuum & boost are 0. I'm going to run through the Boost Control Solenoid diagnostic one more time, then maybe try another new one (could be the new one I used is bad), depending on what I find. I'm about ready to give up until whatever it is shows itself in a more obvious manner.

tloukaitis wrote:

Yes, however, temperature is not a factor as long as I downshift & keep RPMs around 3000, when vacuum & boost are 0.  I'm going to run through the Boost Control Solenoid diagnostic one more time, then maybe try another new one (could be the new one I used is bad), depending on what I find.  I'm about ready to give up until whatever it is shows itself in a more obvious manner.

When you downshift, you lower the load on the engine.  I would do all the tests on the cold engine, then repeat when it is hot.  Compare the readings.  Could the bypass be sticking when cold and free up when the engine heats up?

Vacuum should not be 0 in a lower gear at 3000 RPM. It should be higher due to lower load.

Now that you have the vacuum boost gauge hooked up, do the test for clogged exhaust. With the engine at idle, in Park, fully warm, note the vacuum reading, should be about 20". Now rev the engine in Park/Neutral to 1500 RPM and keep it steady. Vacuum should remain high, at least 15" or more. If you see it drop off, that points to an exhaust restriction.

Larry, yes, correction, on downshift, vacuum is about 10 inches, no code.

Went through all the diagnostics again, cold, everything checks normal. Bypass not sticking. Also, took BCS off & powered it off & on with jumpers. it clicks & opens & closes when required.

Checked for clogged exhaust; vacuum as you mentioned.

Sometimes, a P0171 code is thrown at the same time. Will proceed to check this out & see if they are related.

Thanks,
Terry