AustinT

Hi,

I need some schooling on the VSS.

I have a 89 camaro that had a 305 tbi (8476) ecm. I am converting it to a 749 ecm. My concern is with the Vss. From what I have read the Vss is inline between the speedometer and tranmission. Im not sure if my current VSS will work OK with the ecm swap. To throw another curve in the situation, I have a t56. Ive decided the easiest way to get my speedometer to work is to use a cable X. The cable X converts the pusle signal from the t56 into a mechanicaly driven cable. I know the cable X lags a little under hard acceleration and will not keep up with the true speed of the car.
1. will my current VSS work with the 749?
2. will the lag of the cable X affect the vss
3. Will it matter if it affects it?
Thanks

SATURN5

You can always change to a later 90-92 guage cluster that has a electronic speedo. Rewire as needed. The 749, specifically the $58 code will work with either a optical or magnetic VSS input, just need to flip a flag in the bin. BW

AustinT

Thanks for the Info, What VSS does my car have now optical or magnetic? Im guessing magnetic. Where exactly is the Vss located along the speedometer cable? I really dont mind having a speedometer that lags a little under hard accleration as long as it doesnt throw off the ecm. HMM wander if it would affect Datalogging the speed

AustinT

Thought of one more thing.
when I repin my 8746 harness for the 749, do I need to find the connectors for a 749. In other words will my ecm connectors work in the 749 with a repin?

AustinT

So will the 749 read the pulses directly from the t56?
Is it possible to use the t56 output to run both the 749 ecm and the cable X?
That way I would have a accurate signal for the ecm. speed datalogging would be accurate. And I would not have to replace the dash gauges.

Grumpy

Whatever signal was supplied to the 8476, just pin it to the 749.

I do believe the 476 used an optical input. Easy check is if there is just one wire for the VSS it's an optical input, and if a two wire then it's magnetic.

AustinT

Hi Bruce,

Part of the problem is the VSS and speedometer do not work becuase I put in a t56 tranny. If it would work, What I would like to do is buy the cable X to run the speedometer and run the ecm directly from the output of the t56.
I dont know if I can run the ecm from vss if I use the cable X. The cable X lags a little under hard acceleration , and it would throw off my speed datalogging.

1. Can the output of the t56 be split. One signal to drive the cable x (speedometer) One signal directly to the ecm?

2. Curious, Will the 730 ecm work directly from the t56 output signal as well?
Thank You!

Grumpy

There's no guarantee the sensor will drive both.

Might look at a wiring diagram, and see if the 730 outputs a cruise control signal, and maybe use that for your X cable. That'd let you hook the ecm to the tranny. Your tranny has a two wire VSS, right?. Next issue would be if it has enough scaling to allow for the Manual tranny input. What manual tranny did they use with the 730s?.

AustinT

Yes Grumpy, the t56 has 2 wires for the output. Im not sure what tranny the 730 had. I would imagine it had a t5 for a manual and a 700r4 automatic
Thanks

SATURN5

The VSS wires from a later thirdgen, specifically ones that came with electric speedos should be purple and yellow. The 88 GTA that I used for parts had a electric speedo and the VSS wires were routed to a yellow buffer box. The 165 ECM required a 2000 pulse signal, the speedo used a 4000 pulse as generated by the VSS in the tranny. This buffer box will give you two outputs, one 2000 ppm,(sometimes called optical, as the signal is generated by a LED and a shutter wheel), the other 4000 ppm,(called magnetic, again due to how the sensor generates the signal). Depending on what number of pulses the cable X requires, the second output can go the the ECM. The code can handle either count, so long as its wired correctly (inputs differ between types), and the proper flag is set in the bin.

I'd seriously look into swapping to a later gauge cluster with a electric speedo.. Probibaly cost a whole lot less, and you gotta rewire some anyways.. hehe. BW

AustinT

Thanks Saturn5 for your post, It is exactly what I am looking for. Can you Please go in a little more depth about the Code. I assume your talking about the code in the ecm? Do you mean the 730 ecm or 749?

I would really like to go with the box and keep the gauges I have. If I did change out the dash How would I get my mileage to match again? The car has 39,000 original miles and i would like to keep track of them

SATURN5

NP..

Both..

The common bins for both can flip between types of VSS inputs. Then wire accordingly. Optical (2000 ppm) uses a single wire, while a magnetic (4000 ppm) uses a pair.

Ahh... mileage is overrated..



BW

AustinT

What does NP mean?

Thanks again, I just got done sending emails to 3 of our sponsors for the buffer box. I also emailed Abbot, the makers of the cable x to see what range of input it can use

If the 749 or 730 can use the 2000 optical signal, I know the cable x can use the 4000 ppm ?

SATURN5

Sorry.. being lazy. NP no problem.
BW

AustinT

HI,
I think I might have found the speed buffer box that I need. Can someone tell me exactly where it is located on a 87 ta
Thanks