What is your ppm set at for the gear ratio you have?I have 3:42 gears and my ppm is at 4000 but my ecm is 7mph too high.I'm trying to figure the propper amount of correction.I am very sure the ecm is off by 7mph.

 

I have my Pulse per Minute set to 4,024 for my Road Speed Constant. I found that on my car my ECM was displaying a little faster than my actual speedo. My speedo is actually "bang on". Increasing the PPM to 4,024 made my speedo and ECM match exactly.

If your speedo itself is off, you can look either at trying the "Speedo Divisor" or changing your speedo gears in your tranny. To me, it is more important to have your ECM syncronized to your speedo. And then correct the speedo if it is wrong.

 

I corrected my speedometer with a change to the red vss gear and a few passes by a cop radar thingy and friends cars.The ecm is definety too high by 7 mph.So should the ppm go up to lower the ecms mph?

 

If the ECM is registering too high, then you need to increase the number of Pulses per Minute. If you are registering 77 mph on the ECM and your Speedo shows 71 (and actual 70), I would adjust the ECM to 71 and then correct the speedo (which will also correct the ECM once syncronized) to 70.

In that example I would start by modifying the ppm 4000 x 77/71, and then "tweak" from their.

Lastly, the above info is ONLY for a 7730 with the corresponding VSS. I am uncertain if you can do a similar change to a 7730 using the MAF type VSS.

 

I have an 87 formula so I have the electronic speedo .Thanks for the info.

 

This is something i've been searching and searching on as of late. My speedo is super off. (both ecm and speedo). I changed the speedo gear, and its still off.. I don't want to take the transmission apart..

Now from what I understand, you can change the divisor and your ECM may or may not read "right on", but the actual speedo gauge does NOT work off ECM output.

Am I wrong?

I don't remember a "vss out" on my 730 swap, so I'll have to assume no. I swapped from a 165 to 730, so perhaps there is infact a vss out.

Comments??

Or is dakota digital my only solution?

-- Joe

 

If you have an automatic and are running 3.73 or less (numerically) then there are speedo gears available that will correct everything.

Tim

 

Nah Tim, T5..

-- Joe

 

Is it possible to wire a 6-speed VSS directly to the harness wires that were for the 700r4 VSS and not have to use the Dakota Digital SGI-5 cal box and then just change something in the PROM? The reason I'm asking is I'm having trouble getting my speedo working with the SGI-5 (it's a pain in the rear!).

I think the T-56 VSS is a 40 pulse per drive shaft rev and I need to convert it to a 4000 pulse per mile in order for the ECM to display anything on the speedo. (I may be wrong), but I think thats how it works.

Anyways, is there anything I can do in the PROM to avoid using the SGI-5 box?

THanks,
Mike

 

check out stealth conversions. they sell a multiple ratio cable box. its like $50 and its really handy for matching up wierd combos. once you get the speedometer correct then fix the VSS pulse divisor

 

My speedo isn't cable operated, I have a '91 Z.

 

I'm not real familiar with the t56.But I will not let this post die w/o trying to help more.I'm sure there is other t65 users somewhere on the message board that has gone through the same thing.Your best bet is to find that person.Search the tranny forum,or do a search of all forums with terms like t56+vss.You will find the answer.Let me know if that helps.

 

I'm going to completely re-wire the SGI-5 conversion box to see if that helps.

My question for you guys is: Will turning off VSS diagnostics in the PROM have any effect on speedo working/not working, any effect on the purge solenoid on ECC canister, engine idle, and or air/fuel ratio?

I'm using tunercat with $8D.

I DO know that the VSS does effect all of the above listed, however due to the code caused from the no VSS signal from the SGI-5 box not wired or calibrated correctly, I ended up disabling VSS stuff in the PROM. Do I need to re-enable it?

Also, once the VSS signal reaches the speedo (if I can get the SGI-5 to work), will everything above mentioned still function properly with the VSS stuff in the PROM turned-off?


Thanks again for the continued help!

Mike

 

Anyone?

 

the corvette forum might have the answer.I wish I could help more.

 

http://www.eecis.udel.edu/~dzug/92z2...0-vss4T56.html

There is an option to adjust the speedo with the PROM. However, my understanding is that it does not work if you have gears over 3.42 and there may be a larger variance in the conversion than going with an SGI-5.

 

You can change the ppm count, but that won't effect your speedo in the dash. ECM doesnt have a 'calibrated' output wire.

-- Joe

 

These are the questions that I need help on because I'm confused as to what VSS diagnostics controls in the PROM.

 

Anycare care to take a stab at the above?

 

quote:
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My question for you guys is: Will turning off VSS diagnostics in the PROM have any effect on speedo working/not working, any effect on the purge solenoid on ECC canister, engine idle, and or air/fuel ratio?
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Check your wiring diagram for the vss.If it is like mine the speedo gets the vss signal from the box the vss sig goes to before the vss signal goes to ecm.My speed is ran off the yellow box.the ecm feeds off that box(vss buffer?).So turning the vss diag off should'nt stop the speedo.I think if you turn off vss diag,you'll not get any vss fault codes.But I think the code runs off a lookup table if you don't have a vss signal to the ecm.If there is nothing in the code it will be one less input the ecm has.Not a critical one,but important.My best advice is try to diable the vss diag,drive around scanning to see what happens.