Currently my TPI setup in my K5 Blazer has NO VSS. The truck does run extremely well, no idle problems, etc. However, I have been counseled to install VSS as it is reputed to improve the drivability and mileage - and with an open mind with the hope that it really does improve things I am going to finish up the install/wiring changes this weekend.

For my own gratification, what areas does the VSS influence - fuel loading/curve, etc. Should I expect better gas mileage? Any thoughts are appreciated.

Thanks in advance.

 

I'm pretty sure that all the vss does on a tpi setup is turn off the fans on the freeway and lockup the torque converter if you have a lockup converter. Mileage would increase a little because of the lockup converter. If youre happy with the way it works now I wouldnt worry about it personally. The TPI setup in my s-10 blazer has no vss input.

 

VSS does NOT lockup the converter. I have removed the driven gear in my tranny which is attached to the VSS so the compter has no clue how fast I'm going.... and neither do I since my speedo doesn't work. However, even w/out having the VSS my converter still locks up like it's supposed too. The computer has values in it for low speed and high speed lockup thresh hold but that's not the only factor involved or else my lockup wouldn't be working at all. From my experience the VSS does nothing but work your speedo and tell the ECM how fast you're going so it can limit your speed if your chip still has the high speed fuel cutoff enabled. I doubt very seriously if you see any performance or fuel mileage increases at all.

 

I would like to know for a fact if it does or does not need to be hooked up to the computer since I am running my VSS directly to the Speedo since I ditched the computer last year and went to an Edelbrock carb. I now have a 91 TPI setup without the VSS hooked to the computer and will be installing a new ECM and chip soon and would like to wire up the VSS to the ECM when I do the swap IF it needs to be hooked up. I don't feel like wiring it up and it doesn't need to be.

 

Other than the annoyance of a constant MIL from the lack of a VSS signal to the ECM, the VSS is involved in the following programming steps:

LC295: FCB 60 ; MIN VSS, (60 MPH) FOR FORCED UPSHIFT

LC602: FCB 15 ; If VSS <= Disable C/O; CALIB = Arg, (15 MPH)

LCAC3: JSR LDEA4 ; Ck Vss Every 6.25 Ms

Norm Open Fan set - LDAA L0065 ; Vss CMPA LC67F ; 8 MPH BHI LCC21 ; SKIP PS SW READ IF > 8 MPH

Output Bit Sig', (TCC, CCP etc) FDB $E07F ; SEG 2, Vss Calc

LDF52: LDAA L0065 ; Vss BRSET L0037,$40,LDF64 ; BR IF b6, MCU INPUT STATUS WD; COOL FAN REQUEST BCC LDF64 ; BR IF Vss G.T 35 MPH

TCC LOCKUP - LE20A: CMPB L0065 ; CK Vss BLS LE215 ; BR IF Vss LT 32+5 MPH (COAST)

LE3F7: LDX L00F9 ; RICH OR LEAN o2 DIV TIMER CMPA LC309 ; If Vss > 60 MPH & LV8 > then divert AIR

CCP on to off params LE7A2: LDAA L0067 ; Vss, (MPH/(16/5)) CMPA 0,X ; If Vss < 3.12 MPH Disable CCP

READ MAN AIR TEMP AND CK ERROR 23/25 BHI LEBE2 ; BR IF Vss LT 1 MPH, (CLR ERR 23)

Decl Fuel cut off Tables & Param's LC602: FCB 15 ; If VSS <= Disable C/O ; CALIB = Arg, (15 MPH)



For all purposes, it appears that the VSS does have some input to the EVAP purge control, EGR control, highway fuel and spark modes, cooling fan operation, TCC lockup and forced upshift, A.I.R. divert/port solenoid, and some MAT error clearing. There are probably other functions since the VSS appears in some subroutines as well, and I didn't track down where all of those were used.

It's probably worth running the two wires and connecting it.

 

Jesus Christ. The VSS is that important? I didn't notice any difference in performance when mine was disabled due to the drive gear clip coming lose and that drive gear slipping back into the tranny. One thing I have noticed is that my lockup kicks in too early and when I let off the gas completely lockup goes off. I think both of these are from my lack of VSS but I've been driving 1 1/2 years with no VSS or speedo.

I agree with Vader though, just hook it up it's only two wires. If it were only that simple for me. My wires are hooked up, unfortunately I have to change my drive and driven gear to get my VSS and speedo working again. Maybe this summer it'll get done.

 

Well, how should I hook up my setup?
I have an 86 that that was an LG4 and has the yellow VSS buffer box, 2 wires from sensor in tranny to the buffer and 2 wires out of the buffer to the speedo.

I have a 90-92 Speed Density ECM.

Do I need to use the buffer if I can connect everything through the ECM?

 

I've found this interesting, as to how many guys are NOT using VSS. Interesting.

Guess the big question is how are you guys NOT getting a VSS code set?

Do you have the park/neutral indicator wired together? That is how mine is, so when I do the VSS hookup today, I will disconnect them and/or put a toggle switch between them to tell the computer I am either in Park/Neutral or not.

I'll report back later on my results.

 

I turned the VSS off in my chip so that it does not throw a code.

 

When I installed my B&M megashifter, instead of hooking up the micro switches for park and neutral safety I unbolted the park/neutral saftery cluster from the right side of the stock shifter and stuffed it up under the right side of the console out of the way. The plastic slide connector that would normally move with gear selection is now constantly in the park position. Only disadvantage is that my car will now start in any gear but after almost a year this hasn't been a problem for me yet.

 

OK, the VSS is installed, wired, and operational. The park/neutral indicator wires were wired together to tell the ECM we were always in park/neutral.............hence no codes set. Cut that connection, wired in a steering column microswitch to make that fully operational, and test drove the truck.

First impressions are inconclusive. Really didn't have time to drive it far or for long, as had other projects to work on, but will post a separate post for this feedback for y'all in the near future.

Thanks for the input and information. As long as there is NO negative effect on performance/fuel mileage, the VSS is staying.

 

When I had mine disconnected for a while, I got 3mpg less than usual, and a fuel smell on shutoff. The ECM controls the canister purge solonoid with info from the VSS (I guess that's this line from Vader's post: CCP on to off params LE7A2: LDAA L0067 ; Vss, (MPH/(16/5)) CMPA 0,X ; If Vss < 3.12 MPH Disable CCP [the charcoal canister purge]). When I hooked it back up, all was back to normal (back to 20mpg city, and no fuel smell).