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Old January 29th, 2014, 23:59
CheapXJ's Avatar
CheapXJ CheapXJ is offline
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Electronic speed sensor (VSS) Specs.

Anyone have the nerdy details of these sensors and how exactly they work (reed switch, hall effect, input/output voltages. frequency/pulse count for given speeds etc.

the reason I ask, I swapped an AW4 into my 2000 WJ, and I need to generate a .2v to 5v DC sweep that increases and decreases based on ground speed to mimic the input that my WJ's PCM would see from the governor pressure transducer so it stops bitching about it with the CEL. It's the only problem I haven't been able to make go away. at the moment, I literally have all the electronics from the 42re ziptied up into a plastic bag and wired in direct to the PCM. This got rid of all but ONE code, that motherf**king governor pressure bull$hit.

I will make dummy loads for the solenoids (even though it bothers me that my PCM will be wasting power driving its stupid PWM signal into the governor pressure solenoid)

I think I'll be alright with lockup, but if it acts up now and then, I suppose I could let the WJ PCM control the lockup solenoid (it can't do it direct because the impedance is different enough, but dummy load plus relay tap will fix that easily)

basically, my mission is to mimic all the stupid bull$hit a 42re does so my PCM quits its goddamn whining. It's a shame it whines so much because it drives SO DAMN GOOD now! I have NEVER driven a 4.0L WJ that ran like this. It's absolutely awesome. My goal is to provide all the information to make a 50-state legal conversion. This was a cumulative project between myself and good friend of mine that is a Toyota nut. I think I'm converting him. He loves the 4.0L's torque.

my interest stems from the fact that WJs are basically as cheap as XJs were a decade ago, and decent XJs seem to go for more money. I can find 4.0L WJs with blown heads/junk trannies SUPER CHEAP and they're otherwise still in really good shape. I was always impressed with the WJ as a platform, and now that they've been time tested, I know the problems, I want to make solutions, because even though there are practically a billion XJs on the planet (slight exaggeration, lol) these worn out WJs are pretty much the last real Jeeps, aside from the junk tranny and weak heads, everything else on them is as solid as our beloved XJs if not better. a 200k mile unmaintained WJ still drives WAY better than a 200k mile unmaintained XJ (by unmaintained, I mean shot suspension/chassis hard parts. wheel bearings, suspension bushings, balljoints and rodends)

once I have the r&d done, I will release it, likely under a TAPR open hardware license. Basically what this means is everyone can distribute the plans over the internet, it will be free to build but if someone decides to try and mass produce it and sell it for profit I can sue them out of fukkin existence and we won't have another fiasco like AWshifting which, well. I know it was dumb on my part to just post the design on this very forum, but what goes around comes around, and it made me smile to see Brett fail HARD at trying to capitalize on MY design. (the solution to eliminate the OBDII CEL problems was very easy, but the hell if I'm sharing that. I'll take it to my fukkin grave just because I'm fukkin bitter about it) It's not like I didn't put a ton of work into it, it was my capstone project when I was in college for EE and mine only ever existed on a fukkin proto board!

But yeah, anyone who can contribute useful info will get credited for contribution to the project, it doesn't directly earn ya any money (unless i have to sue someone for infringement, in which case it may), but it's an awesome thing to have on a resume.

But I'm older, wiser and more jaded now. so let's do this!

But now it's time for me to pop outside my hotel and go
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Old January 30th, 2014, 11:06
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sidewaysstarion sidewaysstarion is offline
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Re: Electronic speed sensor (VSS) Specs.

Of course... you could have someone make you a manual calibration for you WJ ecu and not have to worry about all of that BS.
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Old January 30th, 2014, 21:33
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sidewaysstarion sidewaysstarion is offline
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Re: Electronic speed sensor (VSS) Specs.

Originally Posted by CheapXJ View Post
(the solution to eliminate the OBDII CEL problems was very easy, but the hell if I'm sharing that. I'll take it to my fukkin grave just because I'm fukkin bitter about it)
Just put a 1k ohm 1 watt resistor between the TCU solenoid outputs and ground.
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Old February 21st, 2014, 14:41
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kastein kastein is offline
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Re: Electronic speed sensor (VSS) Specs.

Hmmmm. Time to do a brain dump on VSSes I guess.

Alright so there are a few variants.

All XJ/MJ/TJ/YJ/ZJ/AN/most other Dodge VSSes are electrically very very similar.

3 wire type. These take a power supply (5, 7, 8 volts, depends on year) on one pin, a ground, and feed out a pulse train. 8 pulses per revolution of the VSS pinion gear, which works out to 8000 pulses per mile of travel if given a properly chosen pinion gear tooth count.

2 wire type. These are a reed switch and open/close 8 times per revolution. The rest of the specs are the same as a 3 wire type.

There are various connectors available, but all 3 wires are the same electrically and all 2 wires are the same electrically, so just swap/splice the right connector for what you want and you are good to go.

dead-end type. These screw onto a 7/8-18 thread speedo takeoff gear housing, which is exactly like the RENIX speedo takeoff gear housing. They are all 2-wire.

pass-through type. These screw onto a 7/8-18 thread speedo takeoff gear housing, which is exactly like the RENIX speedo takeoff gear housing. They are all 2-wire. The back of the VSS has a second speedo cable port on it, which is annoyingly 5/8-18 thread, so you need an adapter bushing to put a 7/8-18 speedo cable on it, or a cable with a 5/8-18 end at the transmission side.

All 3-wire sensors are dead-end, but include the housing, and all 3-wire sensors use a short speedo gear.

All 2-wire sensors use a long speedo gear, regardless of whether they are passthrough or not.

You can put a 2-wire sensor into a 3-wire jeep simply by wiring the 2 wires between the ground wire and the signal wire, then putting a ~330 ohm pull-up resistor from the power wire to the signal wire.

You can probably put a 3-wire sensor into a 2-wire jeep by tapping its power wire off the same power wire that feeds the TPS and MAP, but I haven't tested this.

87-90 XJ/MJ/YJ, stock: no VSS. Cable driven speedo.
91-92/93 or so XJ/MJ/ZJ, stock: 2-wire dead-end type.
early 90s YJ, I forget exact years: 2-wire passthrough type.
88-93 AN (Dakota): 2-wire passthrough type.
93 or so and later, all vehicles: 3-wire dead-end type.

This is great because you can use a Dakota/YJ 2-wire passthrough sender to do EFI swaps in vehicles that need a cable driven speedo. I did just that, I put a 94 XJ 4.0/custom harness/ECU, 99 XJ NP231 and 8.25, 96 XJ AX15, and a 98 ZJ 4.0 water pump into an 87 YJ with a 90 AN VSS for a friend and have it running great with no CEL.

I'm not sure how you can use this on a WJ, since there's no opening for the VSS on the tcase housing on those, but if you swapped XJ parts, I'm certain you could arrange for it to work.

As for shutting a late model XJ TCU up about the CELs, get at me via PM. I've got some info and some questions and I'm perfectly willing to sign an NDA.
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Please do not PM me about the AW4 info thread unless you have a truly unique question that is not covered by it or info to add. I do not respond to questions answered by the thread.
Definitely do not hunt down my phone number at 3AM, text me about it, and then threaten violence when I am not helpful. It will not get you what you want.
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Old February 22nd, 2014, 09:40
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Re: Electronic speed sensor (VSS) Specs.

Great info Kastein,solved a problem I have been working on.
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Old December 17th, 2017, 15:50
Umguadakitboody Umguadakitboody is offline
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Re: Electronic speed sensor (VSS) Specs.

Excellent info kastein. I have been working on my 1992 XJ Canadian daytime running lights problem and was confused with the Hz readings I was getting from the speed sensor. With one rear wheel jacked up off the ground, at idle in low gear I am getting around 25 Hz from the speed signal. The speedometer has been working correctly at all times.

I previously thought that there was only one pulse per driveshaft revolution. Now that I find that there are 8 pulses it makes sense.

The second new Dorman Daytime Running Lamp module 704-304 just arrived today. I'll take out the other defective new Dorman module tomorrow and hope it this one works. I have previously verified all the wiring connections to the Daytime Running Lamp module.
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Old November 11th, 2018, 01:05
Bherm800 Bherm800 is offline
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Re: Electronic speed sensor (VSS) Specs.

Hey I'm doing a 4x4 swap. Have a 2000 and am swapping I. A aw4 from a 99 and a np242tcase from a 95. The vss connectors are not the same but both are 3 wire. You said just change plugs but how do I know which wire is which they are different colors.
The other issue is the 4x4 selector sensor. I used the 2 way piece on the output shaft instead of the 4 prong one. Can I just wire those together? Anyone have a breakdown or a way for me to figure out which wires are what.
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