I need to make a VSS wheel and sensor mount for my car. from what I have read I need to make a 40 tooth wheel. This wheel will be attached to the diff at the yoke, much like the JTR VSS of similar design. I will be using either a '7749 or '7730 (I have a few of each at my disposal), running $59. What I haven't seen covered is what the actual signal is from the sensor itself to the ECM. What I am wondering is, can I use a DIS cranbk position sensor to feed the ECM this signal? I have several of these kicking around from the 60 degree V6 line. From what I understand of each sends a similar signal to thier respective components, electrically speaking. What I am looking for here is either confirmation that it will work, or that the signals are completly different. If they are the same this would save me some money, and I'm trying to retrofit this EFI as inexpensivly as possible, as much of this will be changed out in the future once I start to change out the IRS for live axle and the I6 for a V6, etc.. TIA

a 40 tooth wheel won't work with a 7730 ECM.
i have a transmission from a pickup in my car & i tried to use the truck speed sensor.
i believe 40 pulses per revolution is more than the 7730 can handle at freeway speeds.
the factory setting for the VSS is 4000 PPM. i had mine set to 76800 for it to read right, thats a huge increase in pluses per mile. with a lower rear gear it would be even higher.
with the 2.42 gear i have, when i got up around 60 MPH the speed reading in the ECM would start to drop. by about 70 the speed reading ECM would show was around 50
MPH. the faster i went, the slower the ECM said i was going.

when i have time at work i plan to cut every other tooth off the reluctor so i have 20 teeth & then cut it again for a total of 10 teeth. by cutting every other tooth each time, i should end up with the 10 remaining teeth spaced evenly apart.
you'll need to play around with the VSS pulse per mile setting to get it close.

using a crank sensor should work fine, its the same signal as what the trucks used.

i don't know if the 7749 would work with a magnetic 40 tooth sensor or not. i don't think it would because its also a slow ECM.

I don't know about the wheel setup, but I can tell you that code59 is way different from the $D8 in what it wants to see ppm wise. stock 3rd gen trans put out 4000 ppm and when you swap to a t56 trans. its much much higher. I think I've read 40,000ppm. but not sure about that number. which I think is right at the limit for $D8. but for 59 the sy/ty seem to use a box that ups the ppm big time, drac something I think they called it. because I have my t56 wired straight into the ecm without a box and I'm working on mph today. I got up to 5000 something ppm setting and I'm 5 mph slow at 80. 5000ppm is on the very low end in tuner pro. now why I'm putting 40k in and its set for 5 and works, I have no clue but I believe the ppm inputs are coded to be very different between the 2. I seem to remember that the t56 has a 17 tooth wheel. being that 17 puts me at the very low end of the scale, 40 mite just work with 59 but as said above, don't think it would with $8D another thing is I thought most crank wheels were missing one tooth. maybe the gm isn't but I think fords are. that would prob do some weird stuff. another idea would be to follow what the add on cruise control does. just straps magnets onto the drive shaft and have the pick up close to them. kinda like what the bicycle speedo's do. only more than one magnet. you could prob just expoy them to the shaft and it hold.

Well I'm still trying to find out more about the actual number of notches, but 40 seems to be the magic number.

Basically I'm mostly worried about the sensor side of it, the trigger wheel will be able to be changed or modified "easily" enough.

7749 will also work with a magnetic VSS, the Sunbird was set-up that way.

There is also the possibility of getting a DRAC module to cut down the input or change it to an "optical" output that that Sy/Ty used. I'm going to need to read the JTR chapter again to see if they are using a DRAC with the 40 tooth wheel.

So basically I just need to make a wheel and sensor mount now, and use the CPS.

I won't be using the crank trigger, just the sensor itself. The wheel will be what ever I make it, 40 tooth, 1 tooth, 89 tooth, what ever.

Magnets won't work unless I use a different sensor. The sensor I will be using is a maganetic sensor and just needs a steel wheel to create the signal.

Six_Shooter, go with the 40 T wheel and the reluctor sensor, then use a DRAC. That will allow you to re-jumper the DRAC for the proper MPH/PPM value to the ECM. Change gears, change tires diameter, just a re-jumper away for the correct PPM.

The $58 code requires the 2000 PPM digital input to the ECM. The DRAC will supply that, along with the signals for cruise & the speedo (if required).

The $8D code has an option flag to use the 2000 ppm digital input, set that and you are good to go.

RBob.

I didn't see exactly what engine and trans you are using above, does the trans have a speedo cable? if so, couldn't use just use one of the feed through cable drive 4 pulse vss units? seems simpler, but I might be missing something.

I looked at that and I do have a VSS adaptor that I made from a FWD tranny VSS and cable through-put, that I used in my Jimmy, it does thread onto the tranny. The problem is this isn't a GM tranny, it's a Datsun tranny, and doesn't use a square tang. The cable is round at the end with a single tooth to engage a slot in the tranny.

I have another Datsun speedo cable that I may look at using parts form to modify my existing VSS, butit may just be easier to make a new wheel to attach to the pinion flange.

i was out doing some tuning tonight and here's what i found for mph on my car running code 59 checked for magnetic pickup.

i have a t56 swapped into my 3rd gen and the speedo sender wired straight into the ecm.(no converter box) with the road speed sensor constant set to 11421.29 the mph in tuner pro was within a 1/2mph of what my gps was telling me. i only took it up to 80mph but it was good there and at all points lower.


i haven't tried hooking up the speedo to the ecm's output yet, so i wanted to double check that the road speed IP pulse divisor is what sets the output to the speedo. since my trans is putting what i think is 40,000ppm and my speedo wants only 4000ppm. i've done the search for setting it up in $D8. do you know if 58/59 is the same as far as the divisor for speedo output goes?





sixshooter, if it would help, i have an lm1 with the rpm cable to log 0-5V inputs. i could prob hook out my speedo's sender wire to one of the inputs and log the output. as long as its under 5v it may tell you what kind of sinewave your looking for. but i have a t56, not the stock 5t anymore. i'm guessing they'd be the same thou.

I don't think that logging the straight voltage will really tell me much.

Do you know how many teeth are on the VSS reluctor wheel in your T56?

The value at $C0F4 only affects the internal software calculation of the MPH. It won't have any affect on the speedo & cruise outputs. For those need to use the divisor value at $C0F2. Aithough I believe that is a coarse adjustment to the incoming pulse train.

I believe the ECM divisor value is only valid when the MAG input on the ECM is used. So it won't have any affect when using the digital input.

RBob.

17 tooth I believe. but if you do a quick search for t56 speedo, its on here.

just to make sure I'm understanding you. the disvior table that's in my xdf now is at $C0F4 and if I change that it will only change the numbers I have to put in the ppm box, that I just got right. for the speedo, since I'm running a mag setup. I could try adding another xdf constaint at $C0F2. which would be a course adj that may get me close? if so, then I want to try because it gives me a good reason to learn how to add things to my xdf. I see you post the address to different people telling then where its at. I'm guessing that's so they can add a table in tunerpro and make the changes. even if the speedo is 5-10mph off. I'd still be happy with it. thanks Rbob

in my first post i should have said a 40 tooth wheel won't work right with a 7730 ECM, my bad

when i tried to use the ECM in place of the DRAC, with the VSS at the factory setting of 4006 PPM, the speed reading in the ECM was maxed out by the time i got to 20 MPH.
to get it close, i had to set the the VSS to 76800 PPM, thats 13 from the highest setting.
with my 2.42 & a 17 tooth reluctor in my car, i would have about 33,000 PPM vs about 78,000 i have with the 40 tooth. i believe a 17 tooth would give me a good speed reading to well over 120 MPH.
im back to using a DRAC on my car & have the switch set to optical. with it like that, changing the VSS constant does not have any effect on the speed reading the ECM shows.
i had to play with the jumpers in the DRAC to get the speed close.