Hello all.

I recently swap my Dana 36 (2.59) diff for a Dana 44 (3.54). Naturally I knew this would throw off the Speedometer, so I ordered and installed the Abbott (ERA) Electronic Ratio Adapter. After install I no longer get any reading just zero. My Vette is a 1993 automatic.

Here is how I installed:
I connected the yellow wire coming from the transmission tail housing, this is the input to the ERA using its white wire.
The ERA blue wire connects to yellow wire leading to ECM.
The DIP switches are set to 010001000111. I am looking for a reduction of .730.
Power is switch and confirmed by Red blinking LED.

Has anyone have experience to confirm the wires need for the VSS signal.

Thanks

 

I would think you reach out to Abbott supplying them with the VSS schematic from the FSM 8A-33-0. You do have the FSM?

 

Thanks for the reply. I don't have the FSM. Where is the best place to purchase? From all the older threads I have read it seems to always be a yellow wire that is used. I have reached out to Abbott just waiting for a response.

 

The other older thread that I read alluded to ‘92-‘93 vss having an issue with the Abbot ERA. While not perfect (and limited), I was able to correct my speedometer with a key stroke and PROM tuning.

 

Check the Abbott converter and see if the output signal is NPN (pulsing ground) or PNP (pulsing positive). For whatever reason a lot of aftermarket gauge companies use NPN or AC sign wave. Except for Intelitronix (PNP or sign wave). So a lot of the aftermarket converters will send a ground pulse to work with aftermarket speedometers. GM factory stuff is hit or miss. Some gauges will work with a NPN signal but most won't.

If this is the issue it's an easy fix by making a basic voltage divide circuit with a couple resistors. This will just make the signal positive instead of negative.

I had this issue when I tried to use my Holley ECU to send a speed signal to my Intelitronix speedo. It wouldn't show any speed. Well Holley speed outputs are NPN. Intelitronix is PNP or AC sign wave only. I didn't end up using a voltage divide though. I just used a speed sensor on the passenger side front wheel to send a positive voltage pulse. Works great now. And it saved the output on the Holley so I used it for something else.

 

How would I check the output for NPN versus PNP? I only have a Fluke DVM. This reminds me of electronic school learning transistors.

 

Did you provide Abbott with the wiring diagram that I suggested? I thought your mentioned wiring was correct using the Hi Signal and find it odd that it didn't work. In the past (prior to China Flu) Abbott was always quite prompt with responses. Did you email or maybe phone? Do you need the diagram to provide it? The VSS is known to be good? Worked before the D44 swap?

 

I wouldn't worry about checking yourself I would just email them and ask. The alternative is just to use two resistors to make a voltage divide and try it. You can't hurt anything by doing it. If it doesn't work you're not out much just a couple cents.

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Yes it worked before the swap.
I did get a call from Abbott and was given an email to use to request help. Left email last night. used info@atrol.com
Just waiting at this point

 

There is some hope. I just found an older instruction sheet from an F body forum. There is an additional 4 bit dip switch, the instructions provided don't mention it. The older instructions I found say it is to select if using a two wire or three wire VSS sensor. Either way the dip switch setting are wrong on my unit. I will try it latter this afternoon. I added the instructions

 

Well that would do it. A three wire VSS is a square wave signal and a two wire is a hall effect round AC sign wave. Completely different signal types. The speedo gets it's signal from the ECU and not the VSS so usually a GM speedo needs a square wave signal.

 

At this point you should be all set. Your FSM was delivered I believe 15 minutes ago. I also sent email!

 

WVZR-1 thank you for the service manual. It is very comprehensive and great value. Anyone reading this reach out to WVZR-1 and get a copy you wont regret it.

 

Ok everyone I am now operational and the speedo matches perfectly with my GPS.

Summary for install:
On a 700R4 with a VSS sensor you will use the yellow wire coming from the tail shaft. This wire must be cut and the Abbott ERA placed inline. The input of the ERA (white wire) should connect to the yellow leading to the VSS. The ERA (Blue) wire must connect to the other end of the yellow wire leading to the ECM (pinD12) . Get your switched power wherever you choose. I installed mine next to the ECM in the engine bay.

The signal from the yellow wire is a sinewave therefore the 4bit switch in the ERA needs to beset to 1000 or on, off, off,off. this switch tells the ERA circuitry how to receive the signal. In my case it was set differently out of the box. The instructions provided had no mention about this. Luckily after hours of searching I found the instructions of a different Rev in a F Body forum. (Lots of Reading!!!!). I also did not find this on the Abbott website, maybe I missed it.

Abbott Tech emailed me for some help but I had figured it out an hour before. LOL

I hope this helps someone in the future.

Oh I almost forgot., if you been contemplating upgrading your differential DO IT! What a difference from 2.59 to 3.54. I wont dare drive this car with ASR turned off. It will go sideways very easily.

Thanks
Flamingolegs

 

Good to see you're all set!