1992 Jeep Wrangler with 350TPI/700R4 VSS Options

Please forgive my noobness. I searched and found some advice, but no solutions.

Here is what I have so far.

Vehicle:

1992 Jeep Wrangler with original 4 banger efi with 5 speed manual

Swap engine:

Blueprint Engines 355 1 piece rear seal. Forged crank/rods/pistons. Dart heads and a tpi friendly cam.

Fuel Injection:

GM TPI from a 1989 IROC. Painless wiring with a 1227730 ecm running speed density.

Plans:
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Remove all original fuel injection related wiring from Jeep harness and replace with painless and keep as neat as possible. I would like to retain all GM TPI emissions so I can get through inspection. Also keep all original Jeep gauges working along with speedometer. Basically keep it as neat and factory looking as possible.

As far as I know, the stock gauges will work with the GM senders. Oil, water, and Volt that is. Speedometer is a different story.

VSS Problems:

As far as I can tell from searches is the original Jeep VSS is a 8 pulse sender of the "Hall Effect" type. The GM TPI is looking for a 4 pulse VSS AC signal, I think?

Possible Soultions:

1. Use and aftermarket ECM that will accept the 8 pulse "Hall Effect" VSS?

2. Find someone to burn me a custom PROM that will work with the 1227730 ecm to accept the 8 pulse "Hall Effect" VSS?

3. Find a complete aftermarket ECM setup to use the 8 pulse "Hall Effect" VSS?

4. In 1991, Jeep used a mechanical speedometer and a VSS. The sender for this year had the mechanical speedometer and electric vss in one unit. I think I can use the VSS part of the sender to run the original Jeep speedometer. Where the mechanical speedometer would normally hook up, I can use a Painless 4 pulse generator for the 1227730 ecm.



I hope this makes sense. Sorry if I have been rambling on, but I'm just trying to wrap my head around this one issue I have with figuring out the VSS issue.
If I had my way, I would like to have option 2. This way I can use as many oem parts and senders.

Thanks for reading.

Pat

I believe that Dakota Digital has a VSS signal converter that will work for you.

That's definitely an option. I was trying to keep it to OEM parts to keep it simple to fix if needed on the road.

I found another option. Maybe someone can tell me if this will work. Install a VSS in the T-Case that will output the required 4000ppm for the GM ECU.

In this post here----> http://ls1tech.com/forums/conversion...l#post12811090

Quote from the thread.

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- The Jeep uses a 3 wire hall effect VSS that outputs a square wave @ 8000ppm. Since the Jeep speedo is spliced into the VSS signal wire the speedo must need a square wave @ 8000 ppm.

- The GM ECM has a square wave speedo output ,with software can be adjusted to 8000 ppm output.

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Then use the output from the GM ECM to drive the factory Jeep Speedo. Can that be obtained through a custom prom?

I have been going through the same issue as I am planning on swapping the jeep ecm for a gm ecm to run my 4.0 in my 93 YJ.
The vss has been my biggest hurdle. After much research and different ideas, I have come down to this:
Replace the tailhousing on the NP231 with the tailhousing from a NP233 from a S10 or S10 blazer. These tailhousings have the required gm speed sensor and a 40 pulse tone wheel. I am then going to install a 4 out buffer/drac module and then also install a aftermarket speedo.

Jeepsandguns,

This sounds like the way I'm going to go as I need a slip yoke eliminator anyhow.

JB Conversions makes a kit for the 231/233 with a GM sender.
http://www.jbconversions.com/product..._short_sye.php

My only question now is can a custom prom be programmed to output 8000ppm instead of 4000ppm on the speedometer output?

Got a little bored today as they called off work because of the weather.
I have one of those 91 YJ speed sensors. It is magnetic and has only two wires. It also should be a 8 pulse.
Anyways I hooked up a 7727 (cause I do not have a 7730, but they function the same) to my test harness and tried hooking the jeep vss to the vss inputs. It did not work. Then I remembered a old thread where there was a issue when hooking up a magnetic vss. The cure was to hook up one wire to ground, and the other wire to pin C6 on the 7730 (or pin B21 on the 7727) and then select the bit "magnetic vss installed". I gave this a try and ta-da, it worked! The adx file showed speed when I spun it by hand.
At one time I tried hooking a 7730 to my cherokee with MPFI instead of a modded 7427, the speed sensor didnt read in the adx. After I did the above mod, the speed read correct. I am running a 2 pulse JTR vss though, so a 8 pulse is gonna read much faster.
I do not know however, if the 91 only speed sensor will drive the 92-95 jeep speedo. The 92-95 sensors are hall effect just like you said. The 91 only vss is magnetic. Those are completely different signals. I suppose you could try, but I would be afraid it might hurt the speedo. You might try asking around on some jeep sites and see if a 91 vss can drive the 92-95 speedo.

However, now that I think about it, your idea of trying to drive the jeep speedo with the vss output of the ecm is a interesting idea, if it does in fact output a signal the jeep speedo could use. I wonder if it would work? Only thing I can think of, is they are using a newer (LS) pcm. I am not sure if the older 7730 can do this. If the input could be changed to take a 8 pulse vss instead of 4, would the ecm then output 8 pulse also? Someone much more knowledgeable about these ecm's will have to answer those questions.

If you can switch the bin to use C6 instead of B9&B10 for the VSS then I would expect the hall effect sensor will work too. The issue may be that a 0-5V signal from the VSS isn't enough to drive the C6 input. It'd be a simple matter of using a transistor and 2 resistors to change the signal level to be 0-12V.

In the LS PCM's you can set the pulses per mile of the speedometer output pin. Default is 4000 but it can be set to any number. You'll have to open the bin/mask in Tunerpro you are using and see if you can change that output for the 7730 with the mask you are using.

The other option is that you set it up so the PCM calculates the speed as double what it really is then that output would become 8000 pulses per mile. You'd have to adjust every table with speed to be double what it normally would.

Also, I'm pretty sure the output of the PCM will be 0-12V so this may hurt the speedometer since the output of the Jeep VSS is 0-5V. Just using 2 suitable resistors can fix that problem.

Ok, please correct me if I'm wrong.

A Hall Effect sensor is of the square wave type.
The Jeep speedo gets its signal directly from the VSS, so I assume a square wave signal will make it work.
The output from the gm ecm is square wave.

Looking at this screenshot of TunerPro, If the "Vehicle Speed Sensor Instrument Panel Pulse Divisor " is set to .5 shouldn't it output double the inputted signal?


http://i274.photobucket.com/albums/j...psv5jjtj0v.jpg


Thanks for all this help with this. I never dug this deep into tuning before. Swapped a TPI once before, but it was a chevy in a Chevy. Piece of cake.

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Originally Posted by lionelhutz

If you can switch the bin to use C6 instead of B9&B10 for the VSS then I would expect the hall effect sensor will work too. The issue may be that a 0-5V signal from the VSS isn't enough to drive the C6 input. It'd be a simple matter of using a transistor and 2 resistors to change the signal level to be 0-12V.

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I'm not sure about having to set the bin, but I know I have hooked the jeep 8 pulse two wire (91 YJ only) sensor to pins B9 and B10 and the ecm would not read it. It did not matter if I checked or unchecked the flag for "magnetic vss installed" neither way worked. But hooking it to C6 does work.

So if this vss works, could you not set the value at 0x15 (vehicle speed sensor) to 8000 instead of what it is now (4006.96)? Would this not make the ecm use 8 pulse instead of 4, and therefore all the parameters that are speed dependent still work without changing them?

I do also have one of the 92-95 hall effect vss's and I also have a old XJ cluster I can use to test this with. The same year range XJ's used the same hall effect sensor as the YJ, so the speedo is looking for the same signal. If I have some time this weekend, I will try to wire it up and hook it up and see if it works.

Boy, if this could work, it would save me the time, headache, and money of having to swap tailhousings on my transfer case and buy/install a aftermarket speedo.

'7730 TBI applications used C6 with a buffered speed sensor while '7730 TPI applications used B9 & B10 with an AC speed sensor.

It appears the Jeep sensor produces a square wave signal with a 5V amplitude.

I believe the GM TBI buffered speed sensor produces a square wave signal with a 12V amplitude.

So, if you want any chance of the Jeep sensor working you need to be able to switch the TPI bin use the C6 input and not the B9 & B10 inputs. Then, hook the Jeep sensor to the C6 input. It appears that switching that "magnetic speed sensor" bit will do this.

Still, you may have to deal with converting the Jeep 5V signal to a 12V signal for it to reliably work. A transistor and 2 resistors would do this for you.

I highly doubt the 4000ppm output signal is just a pass through of the C6 input signal. Remember, this PCM will also produce the 4000 pulse output when using the 40 pulse AC sensor. So, I expect that the PCM will calculate the MPH (or some higher resolution internal reference representing MPH) and then use MPH to calculate the 4000ppm output.

OK, I got some time and played around with the test harness.
I hooked up my 7727 and hooked up the 92 and up jeep vss. I hooked it to pin B21 (C6 on the 7730). I hooked it to a 5v reference and a sensor ground. I then hooked the XJ speedo to power and hooked the signal wire to pin B8 (not sure what that is on the 7730) Thats suposed to be the 4k out.
I loaded a bin to my emulator and gave it a go. With magnetic vss installed checked, it reads nothing. With it unchecked it reads! However, the jeep speedo does not move. I noticed I could spin the vss by hand and could get the speedo in the data stream dash to max out. I figured it was because it was a 8 pulse and not a 4 pulse. I tried changing the value in the bin from 4006.96 to 8000. It did not make a difference. I unhooked the signal wire from the ecm and hooked it to the jeep speedo. It worked normally. I could not get it to go past 15-20 mph by hand. Hooked it back to the ecm and I can max it at 130-something mph. I tried adjusting the parameter for vss all the way to its max and it did not make a bit of difference.
Also, every bin I looked at, the parameter for instrument panel pulse divisor was 0.00. I tried changing it to 1.00, still nothing on the jeep speedo. I tried 0.50, nothing. I went all the way up to 50.00 and still nothing. I pulled out my multimeter and tested the output wire from the ecm on both ac and dc voltage. I get nothing what so ever from that wire.

So my findings so far is that somthing does not jive. Its strange that it will read the jeep vss, but changing the pulse number does nothing. Also nothing is coming out of the ecm on the speed output.

Try feeding both the speedometer and the PCM with the VSS.

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Looking at this screenshot of TunerPro, If the "Vehicle Speed Sensor Instrument Panel Pulse Divisor " is set to .5 shouldn't it output double the inputted signal?

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That's a creative solution. Unfortunately the ecm is not created to do that math. The circuitry inside the ecm is very specific about what is allowed. I'll do my best to get this out correctly on the first try but it's been years since I've had to deal with it.

When using the "optical VSS" square wave input, the signal into the ecm is routed directly to VSS signal in the ecm. This signal was originally designed to work with a 2 pulse per revolution sensor on the speedometer cable. The cable is calibrated to spin at 1000 revolutions per mile so factory parts originally produced a 2000 pulses/mile signal to the ecm. It is not routed to the ecm/pcm 2k or 4kppm output pins.

The "magnetic VSS" signal is an a/c signal. The ecm circuitry creates a pulse each time this signal crosses 0V. As a reluctor tooth approaches then passes the sensor the signal goes from 0V to +V to 0V to -V and returns to 0V. This cycle creates two pulses in the ecm so the magnetic VSS input has a built in divide by two circuit to keep 1 reluctor wheel tooth equal to 1 pulse. The circuit is then routed to the ecm's internal VSS signal and also, separately, to a divide by circuit for conditioning before being routed to two 2kppm and one 4kppm ecm output. The magnetic VSS input does not create a pulse if the signal does not cross 0V so a voltage shift is probably required to use a square wave signal at that input.

There are two constants that are related to the speed signal and they are frequently confused. This is because they are for two different purposes. There is a "road speed sensor constant" which I've also seen labeled as "vehicle speed pulses per mile "or VSS Pulses." This value is used within the ecm calibration to calculate vehicle speed based on input pulses when the magnetic VSS option is selected.

The second constant is the instrument cluster or IP pulse divisor. This constant is used for the divide by circuit which modifies the incoming magnetic VSS signal to produce a square wave out out for speedometer, cruise, or other external components. Although there are 8 bits in this value, only three are used to select the proper divide by ratio. Selecting a wrong value often results in no speedometer signal. Divide by ratios are as follows:

A B C
0 0 0 Divide by 1 (ie for a 4000 ppm VSS)
0 0 1 Divide by 9 (36000 ppm VSS)
0 1 0 Divide by 7 (28000 ppm VSS)
0 1 1 Divide by 11 (44000 ppm VSS)
1 0 0 Divide by 6 (24000 ppm VSS)
1 0 1 Divide by 10 (40000 ppm VSS)
1 1 0 Divide by 8 (32000 ppm VSS)
1 1 1 Divisor disabled, no output

These bits responsible for controlling the divisor are the highest three bits in the byte. So the values to enter into your tuning software are as follows:

0 0 0 Divide by 1 (ie for a 4000 ppm VSS) (0 through 31 or $0 through $1F)
0 0 1 Divide by 9 (36000 ppm VSS) (32 through 63 or $20 through $3F)
0 1 0 Divide by 7 (28000 ppm VSS) (64 through 95 or $40 through $5F)
0 1 1 Divide by 11 (44000 ppm VSS) (96 through 127 or $60 through $7F)
1 0 0 Divide by 6 (24000 ppm VSS) (128 through 159 or $80 through $9F)
1 0 1 Divide by 10 (40000 ppm VSS) (160 through 191 or $A0 through $BF)
1 1 0 Divide by 8 (32000 ppm VSS) (192 through 223 or $C0 through $DF)
1 1 1 Divisor disabled, no output (224 through 255 or $E0 through $FF)

More to follow...

It is my understanding that when you use a square wave sensor into pin C6 of the 7730 you do not get the speedo and cruise outputs at B11 and C1 those only work if you are using a 4000ppm mag sensor into B9 B10 (or whatever the equivalents are on the 7727) There is a nice diagram that illustrates this in the wiring diagram section of the EBL site.

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It is my understanding that when you use a square wave sensor into pin C6 of the 7730 you do not get the speedo and cruise outputs at B11 and C1 those only work if you are using a 4000ppm mag sensor into B9 B10

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Correct for the 7730 ecm. Since this info applies to several different computer numbers, I've edited my previous post to clearly say the optical VSS input is not connected to the 2k and 4k outputs.

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Anyways I hooked up a 7727 (cause I do not have a 7730, but they function the same) to my test harness and tried hooking the jeep vss to the vss inputs. It did not work. Then I remembered a old thread where there was a issue when hooking up a magnetic vss. The cure was to hook up one wire to ground, and the other wire to pin C6 on the 7730 (or pin B21 on the 7727) and then select the bit "magnetic vss installed". I gave this a try and ta-da, it worked! The adx file showed speed when I spun it by hand.

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By wiring to the optical input you basically forced the ecm to read only the positive side of the magnetic sensor's a/c pulse. This might work, but it could also lead to a problem because the mag type speed signal voltage increases as the vehicle speed increases. The ecm may have trouble if the pulse voltage gets too large.

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Also, every bin I looked at, the parameter for instrument panel pulse divisor was 0.00. I tried changing it to 1.00, still nothing on the jeep speedo. I tried 0.50, nothing. I went all the way up to 50.00 and still nothing. I pulled out my multimeter and tested the output wire from the ecm on both ac and dc voltage. I get nothing what so ever from that wire.

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The XDF data definition and conversion formula for this value should not allow floating point numbers. There should also be a note about what that value means. I believe we could edit the formula so it will only allow meaningful changes but I don't know if TP can be setup to only use specific values. I'll explain this more if needed.

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I hooked up my 7727 and hooked up the 92 and up jeep vss. I hooked it to pin B21 (C6 on the 7730). I hooked it to a 5v reference and a sensor ground. I then hooked the XJ speedo to power and hooked the signal wire to pin B8 (not sure what that is on the 7730)

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J&G, I'd Tee the speed signal line off the sensor so it goes to both the speedometer and the optical VSS input. That signal may drive both devices. If it works then the next issue is the speedometer pulses per mile value. With the optical VSS bit checked the code normally ignores the VSS pulse count that you tried changing and does it's own internal check to determine the number of pulses per mile. The check is very simple: The code looks at the speed sensor pulse count and determines if it's one or two pulses per mile. If it's neither of those, it calculates the speed as if the sensor is three pulses per mile. There are several possible solutions to allow an optical speed sensor with other pulse counts to work in non-stock applications but the easiest answer for this situation might be to change the three pulses per mile value to 8 pulses per mile. If you can use TP to manually edit your calibration in the hex editor, you could change $3F93 and $3F94 from 0566 to 0E67 and see how that works. If it's good we could change the XDF to allow modifications to this location by other users for pulse counts greater than two. If you'd like me to make a change to a .bin for testing, lmk.