VSS for GM EFI Conversions

[ThisGuyUKnow]

Guys I just want to tell everyone what I found out after some phone calls to Dakota DIgital and HEsco today.If you are doing some sort of gm based TBI or in my case TPI (especially if it is a junkyard swap) you dont have to bypass the VSS just because you have a Cable driven speedo.

What I found out today is that the GM systems require a vss that puts out 8k pulses per mile. After calling hesco and inquiring about their vss used to convert 4.0s into older jeeps, the 4.0 vss is a gm product and uses the same pulse signal. The 4.0 vss is compatible with the d300 (i know from my 4.0 MPFI swap) and should be natively compatible to the NP2XX TCs alot of us are using (sorry qtrac and d20/18 guys you may have to do some more research).

The Hesco vss with the cable output and the electronic out put is kinda cashy. I couldnt confirm if Dakota digital's GM vss would be a direct match but they only wanted 40 bucks for theirs which is a fraction of the cost of the hesco one. Also the sensor was used in a bunch of dodges so if someone knows the models please post up the years for junkyard diving purposes. The only Jeep that had the hybrid VSS is the 1991 wrangler and as far as I can tell 91 was the one and only year that the wrangler had the hybrid vss.

If you already knew this then sorry for being redundant. If you didn't, I hope you find this helpful

[Jeep Craze]

FYI: There were some Baby Cherokees too that had a VSS and cable driven adapter. I remember seeing them in the junkyard when I was looking for transfercases. I cant remember the years though. I would think in the beginning era of them though like mid 80's?????

Also www.Transmissioncenter.net has some pieces. They list a part #54MG goes inline at the back of the speedometer and sells for $69.00 in the description it says generates 8 pulses.......so how many in a mile????? hope this helps

[Chris P.]

JTR has a VSS available that will fit the D20 and I guess q-trac too?

http://www.jagsthatrun.com/Pages/SpeedSensors_Speedometer.html

[fasteddy]

FYI: There were some Baby Cherokees too that had a VSS and cable driven adapter. I remember seeing them in the junkyard when I was looking for transfercases. I cant remember the years though. I would think in the beginning era of them though like mid 80's?????

Also www.Transmissioncenter.net has some pieces. They list a part #54MG goes inline at the back of the speedometer and sells for $69.00 in the description it says generates 8 pulses.......so how many in a mile????? hope this helps

I think the spec should be 8 pulses per REV, not per mile. Per mile would be useless to the ecu...

[ThisGuyUKnow]

I think the spec should be 8 pulses per REV, not per mile. Per mile would be useless to the ecu...

Sorry guys I got the terminology wrong. Either way just wanted to let people know what I found out.

[JeepsAndGuns]

Actually the GM TBI and TPI use a two pulse square wave VSS. (2000 pulses per mile)

You want #1 in the link Chris P. posted. I was about to post the exact same link untill I noticed he already posted it.

I looked into the 91 YJ VSS myself but found out it sends too many pulses (8 if I remember correctly) I used to have a 91 YJ and remembered the VSS on it and it was the first one that poped into my head, but found out it was too many pulses.

[FSJ Guy]

Bill over @ Binder Planet goes through ALL of this in his TBI FAQs.

For FSJ's and GM TBI, you want the yellow VSS from JTR.

http://www.jagsthatrun.com/Pages/SpeedSensors_Speedometer.html

It's #1 in the picture. It screws into the NP2XX series of t-cases and the speedo cable screws into the other end of the sensor.

I think it should fit the QT's, too, but I haven not confirmed this.

For a *TPI* system, the pulses per rev required may be different.

[ThisGuyUKnow]

Interesting I talked to solomon, the guy that runs this site:http://www.lt1pcmtuning.com/.

He is the one that linked me to the Dakota Digital vss which is 8 pulses. I also called hesco and the fellow I talked to said that they normally use the one found in the 91 YJ i reffered to in chevy 4.3 swaps. I was just sharing what I found out today from these sources but if my info is wrong I will delete the thread.

[gte901m]

Well, I'm not an expert, but this is what I remember.

The 747 ecm that 99% of junkyard TBI conversion use requires the 2 pulse per rotation model. I know this for a fact because this is what I use on my current junkyard TBI set up. I bought mine from JTR.

The 427 ecm used in the '95 model trucks was TBI but used an 8 pulse per rotation model (if I remember correctly). This was because '95 was the first year of the computer controlled automatic trans in trucks, and the ecm required a quicker response time for changes in vehicle speed. I have one of these and a spare harness I have been playing with, but don't have it fully tuned yet (speed sensor input turned off). The 427 also has a faster baud rate for easier tuning via datalogging.

On a side note, there are some ecms that you can alter the code so it will use either a 2 or 8 pulse. I believe the 749 has this ability - I have one sitting on the shelf, but haven't dug into the code yet. There may be other models that have this option.

[FSJ Guy]

Interesting I talked to solomon, the guy that runs this site:http://www.lt1pcmtuning.com/.

He is the one that linked me to the Dakota Digital vss which is 8 pulses. I also called hesco and the fellow I talked to said that they normally use the one found in the 91 YJ i reffered to in chevy 4.3 swaps. I was just sharing what I found out today from these sources but if my info is wrong I will delete the thread.

No need to delete the thread, but I was just pointing out that the TBI system may require something different than the TPI setups.

Good luck with the TPI!

[ThisGuyUKnow]

No need to delete the thread, but I was just pointing out that the TBI system may require something different than the TPI setups.

Good luck with the TPI!

I sent the guy a email back to see if the 8k pulse per mile is specifically for the vette TPIS. I was under the impression tho that the tpi was almost Identical to the TBI computer. I still have to get a hold of a donor harness for my TPI I had a guy that said he could pull it but I have not heard from him for a couple of days so I dont know if our deal is still on.

[Woodchomper]

My '91 Wag used an 8-pole sensor for the cruise control. I know this because I had to step it down (8-pole divided by 4 = 2-pole) to use it as a VSS input for my TBI setup. http://www.ifsja.org/forums/vb/showthread.php?t=70106 I've been running this setup for couple of years and have yet to have a problem.

Anyway, my guess is that if your TPI setup requires 8-pulses then you could use your Waggy cruise control VSS without any modifications. The VSS is located in the speedometer cable near the firewall. I also believe 8-pole sensors are common in Jeep and Chrysler products of the late '80s and early '90s.

[gte901m]

What model ecm are you using for your TPI set up? Then we can figure out for sure what pulse VSS you need.

[Woodchomper]

Here is a link to FSJ Guy's post on VSS options. There is some good info here for those that might be interested.

http://www.ifsja.org/forums/vb/showthread.php?t=112561

[jaber]

I think it should fit the QT's, too, but I haven not confirmed this.

For a *TPI* system, the pulses per rev required may be different.

The Speedo port on all the t-cases is exactly the same, from the QT, D-20, to the NP2XX, they all interchange.