327_TPI_77_Maro

iTrader: (8)

I have an 89 trans am that I can't get the right speedo gear combo to correct the speedo reading so I bought a Dakota Digital box, which I haven't received yet (maybe today)

My question is this: can it convert the signal off the VSS before the buffer, so that I can leave the stock buffer in place to split the outputs to the ECM, dash, and cruise, or does the Dakota Digital box have to replace the buffer? It looks like the VSS is outputting an AC signal...from my limited understanding I don't think the Dakota Digital device can convert that and then output a converted AC signal that the buffer would still read, right?

On my 1989 TA, the ECM gets a 2k pulse, the cruise gets a 2k pulse, and the dash gets a 4k pulse signal. The Dakota digital has one each of 2k, 4k, and 8k pulse outputs...Can I wire the ecm and the dash in parallel off the 2k output and will that cause any problems? Otherwise it doesn't have enough 2k outputs. I don't want to lose cruise if possible...

EDIT: I received the Dakota today. The instructions show one of its functions is to provide a recalibrated AC output for a low speed sensor including a 4000 ppm sensor which the maf TPI unit is. It looks like I can recalibrate the raw AC signal and keep the stock buffer splitting it up and converting it for the ECM, dash, and cruise. I'll report back when I install it over the next few days.

327_TPI_77_Maro

iTrader: (8)

I installed the Dakota Digital between the VSS and buffer like I wanted to, did some math and pre-set the ratio conversion, and it works, within 1 mph of my GPS first try. The only issue I'm having is the needle occasionally jumps while driving, maybe once a minute, and at idle it hovers in the 0-3 mph range and moves around. I read on here someone added a 5v regulator on the line input to the Dakota digital and that fixed it, I am going to have to try that b/c I have cruise and a 700R so I don't want the ecm and cruise getting confused by the jumping.

pzoom

Hey thanks for putting up those pictures!!! I am getting ready to do the same thing to my 91 Firebird. I was contemplating the gear swap versus the box - the box looks easier and the fine tuning a plus since I have aftermarket wheels.

Did you have a fix for the speedo "jumping"? Did the 5V regulator fix it? Did it affect the cruise control?

327_TPI_77_Maro

iTrader: (8)

The 5v regulator didn't fix the jumping needle, and neither did providing dedicated, isolated grounds. I sold the car with the jumping needle. Cruise should work if you wire it this way because you are altering the signal into the buffer, and the buffer converts and splits it as appropriate from there, but I don't recall if I ever tried cruise. I would use gears rather than this box, if you can get the right gear combo, as I was never able to get the Dakota Digital box to work properly, and I know from searching the net back when I had this problem, I wasn't the only one.

LeeH

iTrader: (2)

The needle jumps because of crosstalk on the wires. You need a pair of tightly twisted wires going from the Dakota box to the VSS. Did this on mine years ago and the needle never jumped again.

John in RI

iTrader: (167)

I've got an aftermarket digital dash installed in mine and I'm using an DD box to convert the speedo signal to from the tranny. In my case I replaced the original buffer.

When sitting in "N" the speedo will readout a false MPH reading,..... tells me I'm doing over 100 MPH sometimes on start-up before the idles settles and the MPH drops to shows a slower speed.

As soon as the car is put into gear and moving the speedo begins to operate normally and displays the proper speed. This happened with the 700R4 and the T56 tranny.

I've heard that this can be overcome by twisting the wires really tight together - but never tried it. Will that really work ??

327_TPI_77_Maro

iTrader: (8)

I forgot to mention, I replaced the wiring between the VSS and the Dakota box with a tightly twisted pair, and that did not fix it. I believe it was interference, but I couldn't get rid of it.

LeeH

iTrader: (2)

If you think you are still getting RFI, go to Home Depot and buy some 18g single pair shielded wire and try that. We use that type on a lot of Analog/Digital interfaces at work...

It's been so long since I installed my dd box, But I do remember having those same problems. I know I fixed them, and I thought it was just installing TP wire, but it could be mistaken. I'm dimly remembering grounding the DD box directly to the chassis (I mounted my box under the console right to the tunnel by the console ashtray. Lemme see if I can find an old pic of that...