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Does VSS matter? (you should already know my answer)

dyeager535

dyeager535

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Hell yes! :)

So I'm installing cruise into my truck (not a simple matter, the cruise setup is mid-80's, I've got late 80's TPI, with a '91 205 so no speedometer cable, no idea if the cruise setup is even compatible) and have the instrument cluster out to get to all the wiring and components. After disconnecting everything, installing cruise, hooking everything all back up, and going for a spin around the block, I discover that cruise isn't working. Hmm, guess I need vacuum for the servo lol. So I disconnect EGR, use that vacuum port. Drive around the block, no cruise still. But wait a minute, why is it running so terribly? It's running like it's missing or has a vacuum leak! Lope to the idle, and almost stalls when I put it in gear and ease out on the clutch. Now I need to fix this, worry about cruise later.

Get back to the house, check the plug wires which I might have bumped, check the vacuum line, no problems. (as a matter of fact, with the vacuum port open to atmosphere, it runs just as good to the ear as with no vacuum leak, even when it's running correctly) No cluster, so no idea if I was throwing any codes. Plug the EGR back in clear the ECM just in case there are stored codes, start it up, still bad idle. Damn, now what? For whatever reason, I looked down, and because there was no cluster, I could see the DRAC. Ha! I hadn't plugged the DRAC back in after adding the cruise wire to it.

Connect it back up, clear codes once more, truck back to normal. All is good in the world.

As I always make sure to mention when VSS comes up, some people say they don't run VSS, and have no problems. That could be true, or it could simply be that they are putting up with issues that shouldn't exist. My truck ran, but not as good as it should have. This was my first time running without VSS, and the difference was astounding. Just thought I'd put this out there, I'm sure VSS will come up again, hopefully someone searches before posting and sees this. :)
 
I don't run it... I intend to, just haven't gotten around to placing an order with Jags....

It has not affected the way the truck runs... Not that it's right, or may not screw up other people, but in my case, I seem to have lucked out and had no ill effects that I've noticed...
 
I'm somewhat baffled as to why there is such a large discrepancy in what people state as problems, or lack of, in regards to VSS. I'd heard all the stories about stalling, idle issues, etc., but until it actually happened, I was unsure who to believe.

I still tend to believe that in some cases it *is* probably negligible, (as you mention) but it sure seems odd that on my setup for example it made such a difference, while others just don't seem to notice anything odd at all. In regards to VSS, whether it's TPI or TBI shouldn't really matter, all the same parameters are there either way.

I have no idea what could possibly allow one setup to run correctly without it, yet others have problems. Actually now that I think back on it, I was running an earlier PROM when I first got it running, and DID drive it around without VSS hooked up many years ago, again just around the neighborhood, but no problems. Perhaps I didn't drive it long enough, this time it took a bit of driving until idle deteriorated. The possibility does exist (which is why I won't make a blanket statement on this, except for my particular setup) that there is simply something different in the PROM's that make VSS a big deal or not. But you would *think* they would be consistent. I can't think of anything other than the PROM that might govern this, so there must be some inconsistencies.
 
I havn't had VSS with my TPI and have never had it cause a problem. One day when I start to street drive it more again I will probably install it but for now I have no extra money and it has been fine without it for years. My truck may run better once I get VSS hooked up but all I know is my truck with TPI & no VSS runs WAY better then it ever did with a carb.

Do you NEED VSS probably not or at least no in my case. Should you do it if you can? Yes

Harley
 
I guess to put it in perspective, I guarantee I'd fail emissions without VSS. You could smell how much richer it was running.

I've had that thing running on one bank of cylinders, and it ran just as bad with the VSS disconnected.

Maybe I'll take a (crappy) video with my camera at some point, VSS vs. no VSS. :)

Without a torque converter, you would THINK that my setup would be optimum to run without VSS, since clutch in, there is no load on the motor. Any chance you guys have the idle bumped up? I haven't hooked up a tach to see what my idle is, I can't remember what target idle RPM is for the manual trans setups. It did run ok when moving faster than idle, but the manual transmission doesn't do anything to smooth out the poor idle if in gear and letting it crawl.
 
I passed the AZ e-test with my TPI and no VSS with flying colors. The AZ test is a full test with a roller dyno, visual inspection, gas cap test, tank pressure test, etc. My truck passed VERY clean. It was alot cleaner then my carb ever was even when the carb was dyno tuned for my motor.

My idle sits at abuot 700-800 I believe in neutral and a little lower in gear.

Harley
 
Your idle sounds a bit high, but I'm not a TBI expert. I thought autos were supposed to idle like 550RPM in gear? The testing stations around here have a threshold for the idle RPM, if you go over that, you fail. It's pretty high though, like 10-1250RPM I hear.

With a bit of throttle mine would have "cleared up", so I wonder if that's part of it. Crank my idle speed up.

Not that I need to worry about this, I'm just curious where the variable is that allows some to run great and others to fall on their face. Any chance either of you have messed with idle, or are you running bone stock PROM's?? I haven't changed mine from stock.
 
stock prom.... about 750 in neutral, 600 in gear... 87 vintage... Is yours newer? Thats the only thing I can think of.. newer prom.. higher baud rate...
 
Yeah, it's the '89 PROM, so putting out 8192, bit faster than the 160. Only "hardware" issue I can think of different that might affect it. Still unsure how, since speed is being measured with both...
 
o.k. can i get some info? 87c10 tbi 350 with 700r4 cab on 79 k30 4speed and 205. both had speedo cable and no electric adaptors at all. only thing i can find is a sensor on back of speedo. like the one for cruise that i dont have.

so if this is the speedo input to the pcm then i have a vss?

and if yes then being auto tranny comp chip running man tranny now. will this effect it? and my 79 speedo cable is shot. i need to get a new one. then the speedo will work.

mine smells ritch and its got power but not like it did as a auto before parted out to fix this truck.
 
There are a few variables to why mine might be ok and yours not. The PO had this installed on another motor and was pretty good with dialing stuff in so I imagine he had it running well on his truck and then I got it semi-dialed in. He did a vortech swap when the motor my TPI was on lost a bearing.

I also run MAF not MAP so that might allow for some lead way in runnnig better without a VSS.

My computer is stock as far as I know and my spare computer (yes I carry a spare computer :crazy: ) runs the same as the computer I got with the system.

Via the Painless wiring harness manual my ECM is grounded into the park/neutral modes so my computer thinks it is in park or neutral all the time even when I am running down the road at 65, offroading, etc.

Harley
 
On a manual trans PROM (like mine) there is no park/neutral switch to tell the ECM it's in or out of gear. So VSS is used at all times, but that's all the ECM has/needs to tell if the vehicle is moving or not. Automatic PROM needs to know if the vehicle is in P/N (no load on the engine), in gear (load on engine), or in gear AND moving. (load on engine due to throttle/vehicle load)

Mine is MAF as well, but the park/neutral grounding answers the question. :)
 
sweetk30 said:
o.k. can i get some info?
Click to expand...

Yes. Can't guarantee it's right. ;)

87c10 tbi 350 with 700r4 cab on 79 k30 4speed and 205. both had speedo cable and no electric adaptors at all. only thing i can find is a sensor on back of speedo. like the one for cruise that i dont have. so if this is the speedo input to the pcm then i have a vss?
Click to expand...

All EFI setups (to include the carbed computer setups) use VSS. All C/K (R/V)truck VSS' up to 1989 uses the cable driven VSS on the back of the speedometer. Which is what you have. That does feed the cruise module as well.

and if yes then being auto tranny comp chip running man tranny now. will this effect it? and my 79 speedo cable is shot. i need to get a new one. then the speedo will work.
Click to expand...

Quite often people say the setups run ok manual or auto. Best to match them though, timing and fueling are different between them, as are other things, like idle, how fast RPM's drop when you shift, etc. You'll need to run an '83 (or so, *I* believe that was first year of VSS in trucks) up to 1989 speedometer/cable to make VSS work in your case, or retrofit it. I'd just run the whole new cluster and call it good, otherwise the gauges won't match, unless you don't care. :)

mine smells rich and its got power but not like it did as a auto before parted out to fix this truck.
Click to expand...

Might be part of the park/neutral switch being gone. Did you jump the P/N switch connector, or leave it open? Could also be that something else is wrong/bad, like plugs, wires, cap, rotor, normal tuneup stuff, vacuum leak, etc.
 
I ran with and without a VSS on my 7730-controlled 454. It wasn't even close to a stock program but it helped drivability a bit due to the manual tranny, but it wasn't required by any stretch.

Now on my Vortec 454 I am not running and never did, with an auto trans. No issues whatsoever. Smooth as silk, no codes, etc.

EDIT: I am not running an electronic tranny on the Vortec.

IIRC without a VSS EGR will never function, for what its worth. I say skip the VSS unless you have a cruise control.

Andy
 
dyeager535 said:
I'll have to get video. Simple fact is, if your setup likes VSS, the truck runs like ass without it.

Here's some reading for those that want to learn more. This article is in no way close to complete, but it's something, and I don't have to type. :)

http://www.jagsthatrun.com/V8-chapters/V8-tpi-Speed-Sensors.pdf
Click to expand...

It certainly doesn't hurt to run a VSS, that's for sure.

Andy
 
That is not even close to correct, sorry. Change that to "doesn't hurt MY setup" assuming that everyone who says it isn't harming anything has verified that VSS doesn't affect fueling in their PROM. Automatic transmissions will mask a lot of problems.

I'd be doing anyone thinking about running EFI without VSS a disservice by not saying that.

Don't take that the wrong way: but not every EFI setup runs the same without it, therefore blanket statements like that can't be made.

If it is necessary to disprove the thinking that VSS is always unnecessary, I can , although I'm not sure the camera video/audio is good enough to capture the significant difference.

I would hope people assume I started this thread because there was a very real, significant difference in my setup without VSS.
 
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dyeager535 said:
That is not even close to correct, sorry. Change that to "doesn't hurt MY setup" assuming that everyone who says it isn't harming anything has verified that VSS doesn't affect fueling in their PROM. Automatic transmissions will mask a lot of problems.

I'd be doing anyone thinking about running EFI without VSS a disservice by not saying that.

Don't take that the wrong way: but not every EFI setup runs the same without it, therefore blanket statements like that can't be made.

If it is necessary to disprove the thinking that VSS is always unnecessary, I can , although I'm not sure the camera video/audio is good enough to capture the significant difference.

I would hope people assume I started this thread because there was a very real, significant difference in my setup without VSS.
Click to expand...

Dorian, chill out man! Did you read what I wrote? It doesn't hurt to run a VSS, which implies that when in doubt just run that damned thing. I have much EFI experience and that includes burning my own eproms so you don't need to be condescending with me.

Andy
 
This conversation has been civil, calling me condescending isn't very helpful, friendly or true. :(

I'm not worked up at all. I hope others don't feel I've been condescending, on the contrary, I have been very careful not to make any statements that could be misinterpreted or blanket that could be untrue. My responses to you included.

I'm disappointed that with my effort, I'm still called that, especially when your first two posts contain these statements
I say skip the VSS unless you have a cruise control
Click to expand...
and
It certainly doesn't hurt to run a VSS, that's for sure.
Click to expand...
which somehow I misinterpreted, and my response to those statements is somehow condescending? Everyone here is intelligent enough to scroll back up and look to see if I took those out of context, can't see how I possibly did. Both of those SOUND like blanket statements to me.

Clarify with "if in doubt", that's fine. But you have a used EFi setup you want to install on your truck, where do you draw the line for doubt? My setup is undriveable without VSS, while all the others who have posted say they are fine without it. Do we ignore the minority experience in making a decision? I certainly don't know where I'd have doubt as to when VSS is or is not necessary. Maybe with the 8192 baud setups? Certainly with electronic transmission control or TCC, that blanket statement I can make. Other than that, I don't know, that's the simple fact. And so far no one has been able to discern that either as far as I can tell.

If you can't see where I'm coming from, then let me clarify further: Making sure someone starting from scratch with WHATEVER EFI setup they have, who decides to check this forum, doesn't have problems because of VSS, is my intent. We've got some good information from both sides, and what that information tells us is that lack of VSS MIGHT make your setup run terribly. Or it MIGHT not.

It doesn't matter if it's 1 out of 5 or 1 out of 1000, if you are the one that has a problem with it, it will be a nightmare. Looking at all the posts in the garage regarding TBI problems, can you imagine swapping an EFI setup in your rig, having those issues, and at the same time being unsure if VSS is or is not adding to the problem? I can't with 100% certainty say one way or the other, if I did, I would consider myself irresponsible.
 
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What isn't clear about "if in doubt"? I would start without the VSS unless you have an obvious reason to use it (tranny, etc). If it becomes an issue add it on later. It's not a big deal to do that.

In my expereince it's not needed. In your experience it is.

Andy
 
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