VSS or TPS issue?

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04-22-2009, 02:59 PM
meissen

VSS or TPS issue?

Hey guys,

So, I recently swapped a '95 LT1 & 4L60e into my '94 Camaro.

Car runs and drives great for the most part. It has 30# injectors, CC503, rebuilt transmission (Not sure what all is done to it), a 3400~ stall, and a 98+ 3.42 gear rear end.

The guy who is tuning my car did a basic flash to the PCM to recalibrate for the 30# injectors so I've been OK to drive it around town and get things finished up on it (alignment, exhaust hooked up, etc). I still have the v6 gauge cluster on it so my gauges are out of whack and the speedometer doesn't even attempt to move when I drive it around.

So here's the issue: When I come to stop at a light, the car does not downshift. Whatever gear I had it in when I came to a stop is the gear it takes off in when it starts driving. I also hooked FreeScan up to the OBD port and FreeScan does not show a speed rating.

Could it be that the VSS is bad or would it be the throttle position sensor? Or is it that it just needs the tune and recalibration before the PCM reads the data accurately? I do not believe I'm seeing any codes for it, but if either of them were bad would it throw a code? If so, what code would it throw up?
04-22-2009, 03:19 PM
Spartan7

Did you get the PCM flashed for a 95? The 94 and 95 PCM's are different in the way they control the tranny.
04-22-2009, 05:42 PM
MEAN LT1

Quote:

Originally Posted by Spartan7

Did you get the PCM flashed for a 95? The 94 and 95 PCM's are different in the way they control the tranny.

Really...how so?
04-22-2009, 07:12 PM
Spartan7

The 95 and up PCM controls the tranny with a PWM signal as opposed to the earlier on/off signal of the 94. This has been covered many times on CZ28.
04-23-2009, 08:26 AM
meissen

The PCM, engine, transmission, and engine harness are all from the same car so I don't think that's it.

I ran DataMaster on it and it was giving me DTC24 which is a fault in the VSS circuits... looks like I've got a wiring issue or the VSS is infact bad. And my 1995 OEM Service Manuals that arrived yesterday (w00t w00t - these things are AWESOME!) says when DTC 24 is set, the PCM will default to 3rd gear which explains why I'm not going into 4th gear at all. Once I get that fixed, that very likely could fix my other issue with downshifting.
04-23-2009, 06:55 PM
MEAN LT1

Quote:

Originally Posted by Spartan7

The 95 and up PCM controls the tranny with a PWM signal as opposed to the earlier on/off signal of the 94. This has been covered many times on CZ28.

Im not an a4 so I really dont know. Must have messed that thread. thanks for the info however.
04-24-2009, 12:43 AM
meissen

A good point was brought up by my buddy in Parts & Service at GM corporate. The gear ratio was changed when I swapped the new rear end in and since the PCM is for an automatic it's probably not calibrated for a 3.42 rear end. So, if the rear end speed sensor is reading one thing and the transmission's speed sensor is reading another, it could theoretically cause the PCM to say "I don't know what the eff is going on" and throw a code... Tomorrow (or rather... later today) I'm going to call the guy that's tuning my car and see if he can swing by to recalibrate the PCM for the gear ratio in the back and also tune out the EGR and EVAP. At the very least, it will get rid of 2 of the DTC error codes that I'm getting and hopefully will get the VSS/Speedometer that much closer to being correct.