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Discussion Starter #1
2003 Impala police package with 90,500 miles is hitting the rev limiter in 1st gear around 43-45mph when accelerating at WOT (wide open throttle). Once the rev limiter is reached the engine begins bucking/sputtering/chugging and transmission will not shift into 2nd.

If the driver lets off the accelerator for just a second when the rev limiter is reached then gets immediately back onto the gas, the engine revs as if in Neutral. However, getting off the gas and waiting between 2 or 3 seconds when the rev limiter is hit before getting back on the gas causes everything to work fine - the shift into second will then occur.

When accelerating from a stop in 1st gear at ANY throttle position other than WOT the issue does NOT exist: the 1-2 shift occurs correctly.

No error codes occur when this happens, and no history codes exist related to this issue. The catalytic converter is not stopped up (exhaust was lowered and inspected with a camera). No other driveability issues exist.

A Genisys 2.0 scan tool was used during road testing and the "A" shift solenoid DOES turn off correctly (PCM turns solenoid A off to shift into 2nd), but the transmission does not shift into 2nd.

Transmission fluid and filter were changed, with the fluid found to be within normal limits (not excessively dirty or burned), and no metal flakes were found in the pan. After this service another road test was performed and the problem remained (fluid/filter change did not eliminate the problem).

A known good TPS (throttle position sensor) was swapped from another police Impala with no change - the problem still occurs at WOT, but the transmission will correctly shift into 2nd gear from a stop at ANY speed other than WOT.

Any ideas? Thanks very much.
 

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To me it did sound like the cat was clogged but since you checked that out I believe it could be the transmisson solenoid or the valve body.
Does this happen just when your at WOT going into 2nd or all the gears? These cars do have known problems with the cat and transmissons so its hard to say...
 

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Discussion Starter #4
Frank4202, the 1-2 upshift problem only occurs during the 1-2 shift at WOT. All the other shifts occur correctly at any and every throttle position, even WOT.

In an attempt to temporarily stop the issue, the size of the full throttle stop tab (the little tab on the side of the throttle body itself that acts as the upper limit of the accelerator linkage) was built up using a hose clamp. The clamp serves to prevent the accelerator cable from opening the throttle all the way, but allows it to get very close. In other words, the clamp eliminates the ability to have 100% WOT.

After the above was performed, the vehicle was road tested and ten (10) separate WOT accelerations were performed from a dead stop. Each and every time the 1-2 upshift occurred with no problems without hitting the rev limiter, with the shift into 2nd occurring around 41 - 43 mph.

As a final test, the vehicle was driven at WOT from a dead stop to 100mph with no shift issues whatsoever in any gear at any point of the acceleration.


04DetroitLS, since to date none of the other 9 police Impalas in our fleet have exhibited a similar problem (luckily), none have undergone similar WOT testing in order to compare shift points to determine whether the 1-2 upshift in this particular unit is incorrect (possibly delayed).

A 30+ year GM Master Tech friend (who has not came across this same issue of hitting rev limiter with no error codes) explained that GM police vehicles have specific PCM programming different from their civilian counterparts, which may explain the different/later shift point/speed.

Hopefully this data will provide some additional clarification. Thanks for the replies, and any more suggestions or questions are welcome and appreciated.

To me it did sound like the cat was clogged but since you checked that out I believe it could be the transmisson solenoid or the valve body.
Does this happen just when your at WOT going into 2nd or all the gears? These cars do have known problems with the cat and transmissons so its hard to say...
Quote:
Originally Posted by 04DetroitLS
43-45 in first??? IRRC, top of first is around 35ish could also be the trans press sensor, i have heard of a few of these crapping out lately
 

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Police vehicals come factory with advanced shift points and line pressure.

Along with advanced timing,higher rpm idel speed(for police equptment),and higher top speed limiter.
 

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Discussion Starter #6
PROBLEM SOLVED (was "2003 police not shifting into 2nd at WOT")

Thank you to everyone who replied. The car was dead-lined by the PD for a while, so it became a non-issue... until it was returned to service, when the problem began to get worse.

As metal was found in the transmission fluid pan, a new transmission (installed by the dealer) was the fix. Thanks again!

2003 Impala police package with 90,500 miles is hitting the rev limiter in 1st gear around 43-45mph when accelerating at WOT (wide open throttle). Once the rev limiter is reached the engine begins bucking/sputtering/chugging and transmission will not shift into 2nd.

If the driver lets off the accelerator for just a second when the rev limiter is reached then gets immediately back onto the gas, the engine revs as if in Neutral. However, getting off the gas and waiting between 2 or 3 seconds when the rev limiter is hit before getting back on the gas causes everything to work fine - the shift into second will then occur.

When accelerating from a stop in 1st gear at ANY throttle position other than WOT the issue does NOT exist: the 1-2 shift occurs correctly.

No error codes occur when this happens, and no history codes exist related to this issue. The catalytic converter is not stopped up (exhaust was lowered and inspected with a camera). No other driveability issues exist.

A Genisys 2.0 scan tool was used during road testing and the "A" shift solenoid DOES turn off correctly (PCM turns solenoid A off to shift into 2nd), but the transmission does not shift into 2nd.

Transmission fluid and filter were changed, with the fluid found to be within normal limits (not excessively dirty or burned), and no metal flakes were found in the pan. After this service another road test was performed and the problem remained (fluid/filter change did not eliminate the problem).

A known good TPS (throttle position sensor) was swapped from another police Impala with no change - the problem still occurs at WOT, but the transmission will correctly shift into 2nd gear from a stop at ANY speed other than WOT.

Any ideas? Thanks very much.
 
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