camarorat

iTrader: (8)

I went from 273 gears to 342s. I sent the PCM out for speedo calibration and now the car shifts through the gears to early. It shift from 1st to 2nd at around 10MPH, 2-3 @ 30 35 and 4th at around 40 normal driving. If I get on it, it will wind out 1st to about 30 MPH before shifting to secound, but it bogs. I didn't notice what RPM it shifts at, but I would say it is no where near 6000 RPM. The car ran great before the speedo calibration (with the old tune) The car is an 02 z/28 with bolt ons. Tuner says everything is OK on his end; shift points ect. He seems to think it is TPS problem. If there is a voltage problem with the TPS will replacing it cure it and could this cause the problem?

Tuffguy610

iTrader: (2)

It sounds to me like the car is tuned to shift with 2.73s in it. Since the car now has steeper gears in it, the engine will have to spin faster to turn the tires. Since its shifting too soon, its safe to believe that the computer has not taken the fact that the engine will have to spin faster into consideration. You can look into the TPS issue, but wouldn't you find it ironic that the TPS failed at exactly the same time you had the gears put in, and had it tuned? Maybe somebody else can chime in as well?

RevGTO

iTrader: (12)

The tranny will shift at lower vehicle speeds with lower gears. From what you report, it does sound like it is doing so TOO early.

Is the tuner a known LSx competent guy? What tuning program did he use? Tuning for this isn't rocket science. I'm dubious about the TPS theory.

You can download a demo EFILive from EFILive.com. You can look at the stock tables in the demo version; it may also allow you to do the edits for gear changes and you can compare what they should be to what's happening with your car.

Your best option is to make the investment in your own tuning program, so YOU can know what's going on with YOUR car. Second best is to find somebody locally with HPTuners or EFILive that can do the tuning while you watch and analyze the results.

jimmyblue

iTrader: (11)

Measure the TPS -voltage- (not %) with a meter when
the throttle is full open. Over 4.75V is an error and the
PCM will short-shift the trans for safety. Seen it myself
after setting up my 85mm TB for over-center stop.

If you had 2.73 shiftpoints still in it you'd be banging
the rev limiter, not short-shifting.

camarorat

iTrader: (8)

Thanks, for the replys. This was a mail order tune. After I installed the headers, ported TB, Air box, etc. I sent the PCM out for a tune (tuner is experienced with many references) when it came back I was very pleased with the tune. A short time later I installed a complete rear end assembly with 342s. I drove the car several times after the rear swap, with the 273 speedo calibration and the car ran real strong and shifted great, except that the speedo was off. I sent the PCM back to the same tuner for speedo calibrationand when I installed the PCM that's when the short shifting started.


How do you check the voltage on the TPS? Can you check it with a volt meter?

performabuilt

iTrader: (25)

If it shifted fine other than speedo before you sent the PCM back I doubt its the TPS would be odd coincidence. I would bet somethings incorrect in the tune which does not mean hes a bad tuner hey mistakes happen no matter how good you are, I would contact him immediately and would avoid driving the car as short shifting like that can cause damage to the trans.
Frank at PerformaBuilt

camarorat

iTrader: (8)

I just checked the TPS the reference (grey wire) voltage was correct at 5.0 volts and the Signal at full throttle was around 4.2.. the book calls for 4.5 to 5.0. Do you think that the sensor could be bad?

jimmyblue

iTrader: (11)

If it's as low as 4.2V, maybe your throttle does not
pull to dead center open? 4.2V may also be seen as
less than the 90% (?) required to declare WOT shift
tables to be used, you might be indexing a point in
the part-throttle tables that does it earlier in MPH
and doesn't care about RPM.

camarorat

iTrader: (8)

Well, I ws out in the garage messing around unplugging and plugging just about everything. After I was done I called to make an appointment to get the car in the shop. The owner told me to run it and document at what RPM the trans shifts at normal and WOT throttle. Well now the car shifts like it use to, so I don't know what the problem was. I think I am going to replace the TPS anyway. I am still going to take it into the shop.

performabuilt

iTrader: (25)

Hmm well stranger things have happened possibly bad TPS or since unplugging and pluging in fixed it perhaps a bad connector