nothing past 25

[rick121]

I just finished a drivetrain swap and got to the point i can start and drive the car except the speedometer is way wrong. i'm doing 5 and the car says 90. by the time i hit 25 real speed, im doing 120 on the gauge. at this point the car makes a real odd sound from the tranny area and it doesnt go any faster. it kind of thunks and jolts a bit, but goes no faster. i imagine at 120 the governor kicks in and stops me from going any faster but why would the gauge be so wrong? 1 of 2 things i guess, bad VSS or I put the plug backward. idk how else it could fit, though. 90% sure it's correct. which plug in would it be and what is your opinion on how to approach the problem?

[bigbrian442]

Re: nothing past 25

Re tune the PCM to the correct setting for the speedo.

[rick121]

Re: nothing past 25

supposedly this pcm was pre-tuned to my vehicle when i bought it. I sent the exact vehicle info and they supposedly tuned it at their factory.

[bigbrian442]

Re: nothing past 25

Sounds like someone screwed that up.

[rick121]

Re: nothing past 25

I will take it to Chevy and see, but everything else works perfectly so its hard to believe they set it wrong... unless they put in the wrong gear ratio for the tranny but seriously, off by 90mph?

[bigbrian442]

Re: nothing past 25

The difference between 4000 and 40000 pulses per mile.

[rick121]

Re: nothing past 25

unfortunately most electrical test info is lost on me, i will have to turn it over to higher authority LOL but we'll see. Perhaps they can tune it out at the dealership. if i disconnect the speed sensor altogether will the car run for a test drive?

[bigbrian442]

Re: nothing past 25

The dealer will not be able to do anything except flash it back to stock. Yes, it should run and drive with the speed sensor unplugged. It will set the Check engine or SES light in the dash.

[Bandit127]

Re: nothing past 25

Just be careful though. I had a wet PCM connection and was shorting out my VSS at the PCM. After a while of feeling the t-verter grab and let go about 100x a minute I started to smell hot metal inside my car. The VSS is a very dependent sensor, so make sure its right or run it with it off.

[rick121]

Re: nothing past 25

cool. well i drove it again tonight. realized that it wont shift out of 1st gear. theres only a few things i can think of.
1. Messed up connection
2. Bad ecu tuning (doubt it)
3. VSS
4. bad tranny rebuild.

So, 1st thing to try, flip the connector around and check for any change
2nd thing disconnect VSS and try
3rd take it back to the guy who built the tranny

anything other than paying dealership prices! I can't afford that. thanks for the advice, guys.

[Hib Halverson]

Re: nothing past 25

The difference between 4000 and 40000 pulses per mile.

Bingo! I'd be looking at an incorrect VSS.

The problem is not "bad tuning", nor is it a connector problem. My guess it's the VSS, either a defective one or the wrong one. I'd go back to the guy who built the trans.

[rick121]

Re: nothing past 25

I'd love to if I could get a hold of the guy but I changed the VSS still wrong. Took it to chevy for a diagnostic. they tuned it, now the car denies my key.