P1257

[tloukaitis]

I have a '95 Riviera SC. Keeps throwing P1257 code, but ONLY when car is cold (less than 5 minute warm-up) & under 3000 RPM (2500-2600). If car is warm OR 3000 or above RPM, no code. Happens in the first few minutes after I leave home every day, starting up an incline, boost duty under 100%. Does NOT happen any other time. If I downshift manually to get RPM's up, does not happen. If I drive around the block & do it again, does not happen. Otherwise, runs great! Any ideas? I've replaced everything I can think of pertinent to the problem; MAF, EGR, PCM, EBT, Boost Solenoid & Actuator, H2OS sensor, bad vacuum lines, fuel pressure regulator, injectors, EVAP valve. Thanks.

[Brad Conley]

I found this in a Google search. Only thing else I can think of is a clogged catalytic converter.


Description
SUPERCHARGER SYSTEM OVERBOOST

Normally PCM commands Boost Control (BC) solenoid to operate
at 100 percent (ON) Pulse Width Modulation (PWM) to allow for full
intake boost upon demand. If Reverse is selected, PCM detects rapid
deceleration, or engine is load is extremely high, PCM commands BC
solenoid to operate at zero percent (OFF) PWM.

Symptoms
You likely won't notice any drivability problems.

Causes
Engine torque exceeds maximum predetermined torque threshold
value.
Solutions
Check for restriction in boost signal hose between BC
solenoid and supercharger by-pass valve actuator.
Check for binding by-pass valve, sticking or misadjusted
by-pass valve actuator linkage.
Replace by-pass valve actuator.
Check for restriction in boost source hose to BC
solenoid.
Check for faulty connections or damaged harness.

[tloukaitis]

Here's the latest. I bought & installed a Boost Gauge; here's the results:


1) Normal driving, car cold, scenario as above, no boost present, code is thrown.

2) Normal driving, car warmed up, above scenario, 1-2 lbs. boost, no code.

3) Normal driving, car cold, manually downshift to keep RPMs close to 3000, 1-2 lbs. of boost, no code.


What should this be telling me?

[Brad Conley]

You're beyond me...
I would give Intense Performance a call and see what they tell you.

http://www.intense-racing.com

[tloukaitis]

Correction to #3:

3) Normal driving, car cold, manually downshift to keep RPMs close to 3000, 10 inches of vacuum, no boost called for, no code.

I now suspect Trans. Torque Convertor is locking up too soon, causing engine torque overload. Any ideas how to check this, or change it?

Thanks,
Terry

[tloukaitis]

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.