now we all know the problem of the mechanical driven speedos not working with a T56 due to the electrical output. Can i just get a later model (92 camaro, say) electronic speedometer, or full dash cluster and pop it in and then get the translator box from Dakota digital to correct the amount of pulses?
is this feasible? or could i just get the speedo only, from a 4th gen car and will it fit in the hole in the cluster of my thirdgen dash?
thanks in advance!

 

any ideas?

 

You could try it, but be prepared to hack the hell out of your dash installing it!

Check out:

http://www.camaro.dnsalias.com:8008/84SC/

You'll see a bunch of 91 Cluster images installed in my 84 Camaro. It required extensive modification of the dash and the instrument cluster. But it DOES work.

 

Im swapping my t/a over to electric speedo. I have a future t56 swap planned but for now its even worth it for better looking gauges and a speedo that doesnt bounce. Do these swaps in maros require and modification to the dash or cluster plastics? Mines a bolt on but a wiring mess.

 

90-92 camaros have a diffrent dash then 82-89 ones... and therefore, the orignal has to be cut or replaced with a 90+ to fit.




but to answer the orignal question... yea, use a conversion box and you're set... this is one of the reasons i wanted a 91-92 vert for this project instead of a IROC vert.

 

This would solve your problem:

 

Finished view with VSS sensor, it will also take the earlier VSS or speedo cable drive:

 

Here... since my office firewall blocks port 8008, I wasn't able to look thru and get the exact pic I was looking for. Now that I'm home...



91 cluster grafted into 84 dash.

 

No reason to do so. 4th gens don't use a different speedometer signal. They convert the signal from the trans. and feed the signal to the speedo from the PCM.


The thing about the later models is that the signal provided to the ECM from the VSS is a much lower pulse count than the later model T56. I am not sure on the TBI models, but at least in 91-92 w/ TPI the ECM accepts a signal from the trans. and sends one to the speedo. You don't have that ECM to be able to do that.

As to whether the Dakota has 2 outputs, I honestly forget.

Personally I'd go for the SD TPI swap if you're MAF now, and go for the elec speedo, wired properly and use the Dak. box solely to convert T56 signal to proper input signal to the ECM.

The questions you ask vary depending on what car you have & how it's setup....

 

If you have a 90-92 speed density tpi setup, is it actually possible to make changes to the vss in the chip or do you still have to change the gears?

 

you can probly do it with flipping the switches on the converter box.

 

Those are in 86-92 MAF firebirds, to the best of my knowledge.

 

The adjustments made to the PROM are not "fine tuneable." So while you can use the T56 input to the `730 ECM & correct for roadspeed, and correct for speedo output from the ECM, you may not be able to get the speedo accurate within a reasonable range. That's why I suggest the Dak + the SD ECM.

 

The 4th gen cars do use a different speedo signal. They both use sine wave style sender, but the 4th gens are 40 pulses per driveshaft revolution, whereas the buffer box in a 3rd gen needs either a 4000 or 2000 pulses per revolution signal depending on the year.

I'm not sure what the buffer box does to this signal before sending it to the ECM and then the speedo, but as jmd said I don't think you can fix this with PROM programming.

Everything I've ever read or seen done uses the T56 VSS through a Dakota Digital SGI-5 buffer box to work with the stock speedo and provide accurate readings to the ECM.

 

Theres so many flaws in that statement it isnt funny...

The thirdgen VSS's for the 90-92 tpi, are 4 pulse / driveshaft rev NOT mile, the ecm gets the signal and sends it to the ecm and gives the speedometer a 4000 pulse / mile signal, 2000 pulse / mile to the cruise control module,

LT1 cars the auto gets a 40 pulse / rev, T56 a 17 pulse, computer still feeds 4000 pulse / mile to the speedometer.

 

I could have been clearer, but to clarify...

no, they use a different VSS signal. The signal to the electronic speedometers remained the same from 3rd to 4th gen.


The third gens are either 2002 pulses per mile or 4004 pulses per mile Huge difference between that and the many pulses per driveshaft rev. of the reluctor ring setups.


Oh, it's doable to convert the T56 signal down to a usable signal for the `730 ECM. But, my experience is that either the road speed input or instrument panel output (can't remember which) adjustment is a "rough" adjustment, instead of a "fine tunable" item. When doing a PROM for your TPI car, having an accurate road speed does matter, and needless to say, an accurate speedometer matters. I'm sure there are combinations (tire size & gear) which are close enough that you can do 100% of the T56 signal processing through the ECM. I've just not worked with any.


Personally, I think a 2nd ECM used for signal processing only would do it.

 

Wrong. It's 4004 ppmile. Hence the reason for speedo gears in say, a 92 Z28 trans.

In a 90-92 TPI, yes. I believe the TBI electric dash third gens and 86-89 firebirds had a DRAC to do the outputs to cruise and the speedo.


Exactly my point above, and thanks for the refresher on which box got 17 / 40.

 

So the speedometer gets the same signal from the ECM in both 3rd and 4th gen cars, but the VSS signal is different. Okay, didn't really understand what you were saying.

Yeah, the signal pulse info I was working with came from a website. That seemed a bit on the high side. Mr. Skulte I found an error on your site...

So, the problem with making the conversions on the PROM is that the logic is too course. Does this by chance have anything to do with the 8-bit logic? The idea of using one ECM as a filter is a good idea. Plus, I can go pull another ECM from the junkyard and route the signal through it a lot cheaper than I can buy the SGI-5 box.

 

No.


So long as you can do proms, yeah. For 80$, the box is well worth it though, given the time to wire in & do a prom for another ECM to do the job. Time is money.

 

So, what's the problem? Why would you need to run another ECM? I'm fairly computer savy, so lay it on me.

A good friend of mine is completing his degree at NJIT, so he has access to a super electronics lab. Programming ICs is not a problem.

 

Since the road speed accuracy doesn't matter on an ECM that's not controlling an engine, you could add to the road speed correction, and subtract from the instrument panel correction, and get the T56 signal converted to the ideal 4004 ppm. It might involve the road speed appearing to be an extremely incorrect number, but it doesn't matter as long as that value is not hitting 255mph (which is the highest you can set the speed limiter.)

 

90-92 camaros got the speedometer signal from the ecm or buffer box depening if tpi/v6 or tbi, early ones the drive was on the back of the speedometer cluster that fed the ecm.

 

So you would use the 2nd ECM as a conversion prcoessor only. In other words you would adjust its input and output tables to allow it to provide the proper input for the ECM that was running the car.

Can't go above 255 though. Damn 8-bit logic.