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TPI (With Video)

noahrob

noahrob

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I'll have some video of our first day offroad as soon as I can figure out how to compress it down. Pretty fun, still getting code 36 so I gotta chase down the open, but I also got a 24...Very weird since I don't have VSS..?
 
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I found that without having a VSS you end up with some idle issues when coming to a stop after driving. You may also have issues with the truck dying when coming to a stop. The computer needs to know what speed you're going to correct IAC counts and it can't do it without a VSS. This is why you're pulling a code 24.
 
What if I just say the heck with VSS? Why would it sitll throw the code if the wires are looped together?
 
Because the ECM isn't getting a speed reading to adjust the IAC.
 
Ok, but since it doesn't have one, I assume it didn't have one in Kevin's truck...whcih means I need to either figure out how to get it to work without it, or get one and figure out how to get it to work....
 
Easy enough if the wire is there for it to hook to. The VSS screws onto where your speedo cables goes into your t-case then your speedo cable screws onto it. The VSS has wires coming off of it that should plug into a mating plug.
 
Rob, you're running speed density right?

If so, you need to get yourself a speedometer from an 83+ truck that has the little green box hanging off the back of it. That is a 2000 pulse per mile speed sensor. You can take its output, and send it to pin C6, then have your prom modified to tell the ECM to accept an optical 2000 PPM speed sensor input instead of the stock magnetic 40 pulse toner ring setup.

The 40 pulse toner ring actually generates varying levels of voltage from 0 to several hundred volts or so. If you just splice the two wires together, the ECM will think that you are stopped at all times, which will cause the problems mentioned above.

If you are running good old Mass Air, then just send the VSS output to pin A10, and call it good. No chip changes required.

By the way, the engine sounds fantastic in the video! You outta be proud! Just got a few more bugs to work out yet, and you're set!
 
Thanks, I am running MAF...so sounds relatively simple, just need to get the little VSS sensor for the transfer case...funny thing it that I have exactly 32 miles on my odometer...the cable broke many years ago and I never replaced it..
 
Yep, that would keep your 100 mph speedometer instead of switching to the newer 85 mph speedometers... Maybe see if you can find some way of running a two peice cable to get the sensor up and out of the way of mud etc, can't imagine it'd be so good for the thing to get soaked in a mud hole, lol
 
I just need the VSS to work, I don't case about the speedo...

Were the VSS sensors on any mis 80's tranny? Will it work the same from a TH350 or whatever was in a Camaro to Np 205? I think the fittings are the same for the speedo cable...
 
AFAIK you will NOT find the VSS setup you need anywhere...GM went straight from reading it at the speedo, to generating the signal at the trans/transfercase. (this is why cars have "4 out" buffers and so on, while later trucks have the "DRAC")

Make it as easy on yourself as you can. Find a truck from as late in the '80's as you can, gas model speedo. (old body style only, 90-91 will not work) Truck needs either FI and/or cruise control. The VSS buffer (yellow or light green box) will be hanging off the back. That box needs 12V ignition, ground, and the remaining wire to A10 on the ECM.

For all the ECM cares, you could remove the needle/face from the speedometer and tuck the assembly in the dash, as long as the speedometer cable turns it. If you have to have a speedo that works (at least the VSS portion) and have the stock cluster, you could also just drop the 85MPH one in placeof the 100MPH, I believe as long as the cable is clip-on and not screw on, it will fit.

Painless my a$$
 
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If you are willing to put some effort into it, you can retrofit a VSS into some of the older 100 mph speedos, I did so for my truck :)

If you want to keep the speedo running, and can't retrofit, then just get one of those inline VSS sensors from jagsthatrun.com. use a two peice speedometer cable, and stick it between the joints of the two cables, that should get it up and out of the way of most of the elements...
 
As usual, thanks guys...I will check it out. From what you are sayinng, VSS is not optional, it pretty much is mandatory...
 
Yep, GM wouldn't have put it there if all it did was look pretty :D

About the only thing that is truely useless, in my opinion, is the AIR system, and that is only becuase I am not running cats.
 
Great, so I have teh VSS module in place, but no wire, can I just run a wire form the VSS to A10 on the ECM connector? I realize teh VSS has two wires, but I am pretty sure the other one is just a ground...
 
You need 12V, ground and the output wire to A10.

Sorry, can't help you on the wiring schematic of the VSS buffer, but I *think* it is in the various wiring diagrams to be found online. The '85 or '86 wirind diagrams over at thirdgen should be adequate.

Beware, there are at least two different VSS buffer setups, again, unsure what the wiring differences are. I just know the connectors don't all interchange.

Also, did painless have you ground the park/neutral input? That may also limit the effectivess of adding VSS. Nice to know the vehicle is moving, which is why Painless has you ground the P/N switch, so the ECM *doesn't* know the vehicle is moving, and assumes there is little load on the engine, which is where the idle decel problems come from.
 
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