VSS settings, pulse generator - T400 E38 ecu

[jamesdt]

hey guys, i have an LS3 enigine, E38 ecu and using a T400 transmission.

Im using a pulse generator from dakota digital so the ecu can see speed. The original values were 40 in the VSS p/rev, at this value the ecu does not pick up any speed when im traveling at a cruising speed.

I have now got the value down to 1 but even at this lowest setting i can not get the ecu to see more than around 40km when my vehicles actually doing arond 90km on the road. I have put in my diff gear size (3.91 and correct tyre size 502.00)

This may have something to do with the gear reduction for a "cable driven speedo" in the T400 as the pulse generator is not getting a true figure coming exactly from the output shaft of the transmission.

what is the best way around this? do i opt for finding the smallest driven and drive gear for the speedo so the pulse generator is getting more pulses per tail shaft revolution and then adjust the VSS p/rev accordingly?

Thanks

[will15]

Im not sure about the e38 but on a ls1 computer the vss needs to be a AC wave form pattern. What are you using AC or square wave, last time I checked I couldn't get a AC pulse generator from Dakota digital, so I used a AC pulse generator through a square wave adjustable ratio box works great on the th400.

[jamesdt]

The e38 is expecting an AC voltage (two wire)

http://www.dakotadigital.com/PDF/SEN-01-1.PDF

on a transmission like a 4l80 and 4l60e there is a 40 tooth reluctor wheel on the output of the tranmission so with one tail shaft revolution there would be 40 pulses (a more usable value. Im not sure how many pulses i am getting per tail shaft revolution but i would say its bugger all given the speed i can acheive on the scanner.

[MikeOD]

Can you figure out what the reduction ratio is between the trans output shaft and the Dakota Digital sensor?

[gofastwclass]

I just had to do a similar thing several months ago. I used an SGI-5C between the signal generator and E38 to convert it to a sine wave and boost the output.

[jamesdt]

Mike I could work out the reduction ratio, but I'll have to pull out the speedo drive and see how many teeth are on the drive and driven gears.

I'm actually wondering if all I really need to purchase is the dakota digital sen-01-128 sensor...

I would have liked to have pressed on a 40 tooth reluctor and used an ac delco speed sensor but no one sells them anymore.

Below is from dakota digitals website about the 128k sensor.

High-Frequency GM-Style Pulse Generator

The missing piece of the increasingly popular early-GM transmission swap!
With late-model GM transmissions containing an internal speed sensor outputting 128,000 Pulses Per Mile, the stock 40-tooth (40 pulse per revolution) reluctor ring provided the factory ECM with a high frequency input. The SEN-01-128 can now recreate this missing high frequency rate when converting to an older style transmission with a mechanical speedometer output.

With a standard female 7/8” thread-on fitting, the SEN-01-128 fits all GM transmissions with a mechanical speedometer cable outlet. Removable weather-tight 10’ cable provides for simple installation and cable routing. 128,000 Pulse Per Mile Square Wave signal output is direct replacement for the stock GM internal speed sensor, allowing the ECM receive the signals it needs for proper operation.

Fits GM transmission models with 7/8” Male Threading, ie: TH350, TH400, 700r4, 2004r, etc.

[jamesdt]

months down the track I still haven't found a definite answer. I don't know of any one else that's used the 128k sensor and had good success.

I have been able to get the vcm scanner to read the true road speed but in doing that I had to set the vss pulse per rev down to 1 and had to set the diff ratio to 1.70 instead of the actual 3.91 I'm running. (I did remove the speed sensor off the turbo 400 to see how many times the speedo drive turns per tail shaft revolution. You pritty much need to turn the tail shaft 2 full revolutions to get 1 revolution from the speedo driv

The next issue is trying to get a usable pulse/frequency that the original speedo wants to accept which has been difficult. Even using a digital speedo corrector and boosting it to read 99% more, it still does not read enough speed on the dash where the scanner is reading correct.

[gofastwclass]

Yeah, the GM gear driven pulse sensor was a couple year, two vehicle, very specific optional part and thus non-existent and I couldn't get my hands on one. Wasted a bunch of time looking for that.

There is a GM pulse generator that requires a reluctor wheel on the output shaft - but it is designed for a transmission with a different sized hole. Grrrr.

I wanted to try a SEN-01-128 because in theory it should work, and according to Dakota Digital's site it's the bloody Holy Grail for this application but I couldn't find anyone with one in stock at the time. Every vendor I contacted (including Dakota Digital themselves) didn't have the SEN-01-128 in stock and most were just middle men using Dakota Digital as a drop shipper. Grrrr.

Did you try the SGI-5 like I listed above? I got the E38 working with the SEN-01-1 coming off an older transfer case into an SGI-5. The customer had a mechanical speedometer and was originally going to swap to a digital speedo, but changed his mind and wanted the interior to look factory. I was able to get HPT to read very close to the posted speed on the dash with this combination which I checked against my GPS as accurate.

Mine was a pain because I had a 4L60E that wouldn't shift unless the PCM / TCM knew how fast it was going. Since the 4L60E was mounted to a 1985 transfer case and the dash was mechanical, I had no factory reluctor wheel to pull a VSS signal from. I couldn't use a front hub since there were no ABS hubs available for the vehicle and nothing would retrofit without a LOT of fabrication.

[Hotrodclint]

Yeah, the GM gear driven pulse sensor was a couple year, two vehicle, very specific optional part and thus non-existent and I couldn't get my hands on one. Wasted a bunch of time looking for that.

There is a GM pulse generator that requires a reluctor wheel on the output shaft - but it is designed for a transmission with a different sized hole. Grrrr.

I wanted to try a SEN-01-128 because in theory it should work, and according to Dakota Digital's site it's the bloody Holy Grail for this application but I couldn't find anyone with one in stock at the time. Every vendor I contacted (including Dakota Digital themselves) didn't have the SEN-01-128 in stock and most were just middle men using Dakota Digital as a drop shipper. Grrrr.

Did you try the SGI-5 like I listed above? I got the E38 working with the SEN-01-1 coming off an older transfer case into an SGI-5. The customer had a mechanical speedometer and was originally going to swap to a digital speedo, but changed his mind and wanted the interior to look factory. I was able to get HPT to read very close to the posted speed on the dash with this combination which I checked against my GPS as accurate.

Mine was a pain because I had a 4L60E that wouldn't shift unless the PCM / TCM knew how fast it was going. Since the 4L60E was mounted to a 1985 transfer case and the dash was mechanical, I had no factory reluctor wheel to pull a VSS signal from. I couldn't use a front hub since there were no ABS hubs available for the vehicle and nothing would retrofit without a LOT of fabrication.

Pm sent