The VSS, PCM and you.

[kingbobdole]

Not sure how well this has been covered here, but I thought I'd share my experience. In my past swaps I never really hooked up the VSS to the PCM as I felt, from power values and drivability, that it really wasn't needed. My XT-6 was no exception, so when I installed the EZ30D, I skipped the VSS input to the PCM.

 

The 6 was different though, and the car had trouble making power in the 3k to 4k RPM range. At 4k RPM, the car would take off, and in lower gears, spin the tires. I took it to the dyno to get this:

 

 

As you can see, and I could feel, at about 3400 RPMs, the car actually LOST about 10 Ft/Lbs of torque, then dumps a ton of fuel and the power gets back to where it was at about 3900 RPMs.

 

Recently, I did a dash swap and decided to run that wire over to the PCM. I should have done this originally is all I have to say, drivability is GREATLY improved and there is no more power loss. I took her to another dyno and WaLa! no more power drop. The power band really does still start in that area.

 

 

So the next time I wire up a car, I will totally "waste" the extra few minutes and run that wire.

Edited April 24, 2010 by kingbobdole

[iluvdrt]

That first dyno plot is something else. I cant stop looking at it, I don't think a 4 y/o could have drawn something more wierd looking LOL.

I would have never guessed the VSS wire would be that important.

[monstaru]

wow, that could have been the prob, with the wrx setup i had........good points wedge man...cheers, brian

[GeneralDisorder]

That is exactly the reason I have always stressed that folks hookup EVERYTHING. You just have no idea what the software engineer's used that input for. Besides an annoying CEL - you just don't know because you can't look into the code. All the non software engineer's around here scoff at my anality with regard to sensor inputs but there's damn good reasons for what I say and I speak from experience.

 

Glad you found all that lost power though - that's a win.

 

GD

[Numbchux]

yea, obd ii cars do use the input. I have heard of stumbling and hesitation issues without the VSS. I noticed zero change with my obd i swap....but I'd still hook it up were I to do it again.