Thread: how to get MPH reading on RD1 accurate?

Like the title says...I have a B14 running nismotronicSA as well as the RD1 as my cluster replacement. My buddy and I have pretty much worked all the kinks and everything runs/displays as expected except for the MPH. I wired the vss signal directly to the ecu as I no longer have the cluster to run it thru and the MPH is vastly off! I'm thinking it's cause I'm using my b14 vss vs. A particular b13 vss?!? Any insight on how to tackle this issue would be greatly appreciated

Is the MPH reading stable and change linearly with vehicle speed? If so, we may be able to correct the reading with the "VSS UPDATE RATE" setting. If not, then you will need to use the speed sensor circuit from your B14 cluster to condition the signal for the ECU.

I believe @se200 tried that option as we were thumbing thru things. Im trying to avoid going back to the stock cluster as ive already dissected it but if I must then at some point I will. I was thinking the digi vss out of the 93-94 b13 would do the trick as they give off a different signal but my main issue is I dont know what signal the ecu gets from the cluster itself. If I knew that then it help on how to go about tackling the issue

Some VSS's produce a 0.5V AC signal and some produce an ON/OFF signal switched to ground. From the FSM's it looks like the AC signal sensors are connected through the cluster to the ECU, and the ON/OFF sensors connect directly to the ECU. Both connect to ECU pin 32. I believe the '91 G20 has the ON/OFF type, which might work for you, otherwise you might be able to remove just the speed sensor circuitry from the cluster and wire it in.

So the cluster converts it to a on/off signal and that is how the ecu reads it. So since I bypassed the cluster I now need to find a on/off vss. This out to be fun lol

I think the 91 g20 is cable driven so that makes it a no go for me. The ecu reads the signal in square form and not wavy waves(analog). So I think my best option would be the b13 digital vss

Figured out how to make MPH work....even though none of the vss's work....