Hey guys new member here working on a setup some of you may be interested in. It's not actually an LS1 swap, but rather a 6.6L Duramax in a boat built by PPE some years back. However the issue I'm attempting to solve would work great for any GM retro engine swap, if I can work it out..

Deal is, boats don't use an automotive style transmission, so no reluctor ring options to pick up a VSS signal from. Typically boats use a pressure sensor or small spinning pulse wheel on the haul to estimate speed. Newest fad is GPS speedometers, but this still lacks an output for the ECM to read. That's where I'm at now, trying to adapt a GPS signal to the two wire GM VSS ECM input.

There is a couple nice units available out there now that use a small GPS unit and a NEMA data to pulse output converter setup. These basically read the GPS speed data and converts it to a pulse per mile output used by many electronic speedometers in street rods and such. Cool little devices.

Sky Drive GPS is one unit that calibrates itself to the speedo of choice.

Intellitronix GPS speed sensor the one I've chosen has a set 8000 PPM output and is a good bit cheaper option. Since I use EFI Live for tuning, can just recalibrate in the ECM.

Now that I have a unit supplying an 8000 PPM signal onboard, I need to convert that single wire analog output signal to the correct two wire input wave signal for the 05 ECM to read it.

This is where I need some help and options... Been reading about the early 90's GM DRAC units, but not sure if or which one of those would do what I want. So figured I would post it up here for suggestions, since most of the related searches keep bringing me here..

If I can convert the 8000 PPM signal to correct input for the ECM, this eliminates the need to modify the transmission speed pickup, or add a ring and pickup to the drive shaft for most GM engine swaps. Could be an easy VSS plug and play setup for under $200, long as you can tune your ECM to match the PPM.


Thanks

-K

 

Update:

I just recalled something from working on this layout a while back. The issue may be I need to convert a square wave output from the GPS speed sensor unit to a sine-wave output that the VSS high pin on the ECM is looking for.

Sound correct?

-K

 

 

Yes, the ecu only reads an AC sine wave.
Just curious why you need a VSS on a boat. The issues encountered on the gas motors lacking VSS are unlikely in a boat.
And what trans/drive are you using? It may be easier to add a VSS and reluctor. I'm using the reverse gear in a T10 4 speed as a reluctor and added an aftermarket VSS.

 

Getting the VSS signal working for the ECM allows the ability to estimate MPG, along with controlling several parameters in the Dmax tune that change with load and speed. If you change prop pitch [which I do often] it's like changing gear ratio's, so a shaft speed won't cut it. Plus boat speedo's are typically very unreliable.

I am gonna speak with Intellitronix about changing the wave output in this unit, however I just found that Dakota Digital now makes a GPS-50-1 with the ability to switch wave output by a dip-switch. If it does everything they claim, it's the one to go with because it also does high res 128k ppm output, for under $200..


Cheers,

-K

 

Cool little unit. Just an fyi, there is a minimum voltage the LS ecus require to read speed. On the VSS, it's determined by VSS/reluctor distance and reluctor speed. Guessing an amplifier would solve that with the DD unit.

 

Would ya happen to have any details on the voltage spec the ECM is looking for? Might help when speaking with the tech support guys on these.

Since all of these GPS pulse units are single wire output, I should only be concentrating on feeding the VSS high port correct? VSS low would remain open?

-K

 

I was checking voltage when it wasn't working (VSS/reluctor distance was too large), but newer checked once it started working.
The OEM wiring had 2 wires to the ecu. Some of the aftermarket VSS units I looked at had 1 wire grounded to a shielded cable and the metal VSS body, so I'm guessing the other should be grounded to the DD unit.

 

the Dakota Digital SIG-5 wll convert the square wave to a sine wave for you.

My ford speedo needs an 8k PPM square wave signal to operate and the GM ECM needs a 4k PPM sine wave. SIG-5 is what I am using to convert those signals.

 

So what have you found to work anything? I'm doing a LS1 in a 87 Chris Craft , and would love to stay MAF rather than speed density If I can . a VSS is needed in order to do so . What are your current findings?

 

It's done...

Received the DD GPS-50-1 today, a quick bench test showed it's the compatibility winner.. "Speed 2" position is the correct sine wave A/C pulse output.

First I connected it to the E60 ECM's VSS/High pin with no luck, switched to VSS/Low and it registered a speed on EFI live scan tool. Seemed backwards to my recollection, but unsure that I tagged high/low correct in the new harness build either. Anyways left the vss/high wire OPEN and it works fine.

Then I mounted gps unit under the dash [not a water tight unit] and hardwired it all in. Pulse options are 4k, 8k, 16k, 54k, & 128k options. When you select the correct speed pulse option it sends a 60mph test signal to the speedo ports. Mine was showing 59.7 mph with 128k pulses per mile set up in EFI. A quick speedo calculator "fine tune tab" adjustment and I came up with 127360.000000 PPM. Reloaded the new ECM parameters, now digital speedo and VSS pid are showing spot on 60.0 mph..



Hooked the boat up to the truck and towed it up the road to complete the built in accelerometer positioning learn process. The accelerometer kicks in to provide a speed pulse if you momentarily lose GPS signal like in a tunnel. While in tow I checked the DD unit against a hand held GPS, tracked perfectly up to 55mph.. So I'd call this the best bang for the buck speedo fix out there today. Since it also has another DC pulse output port, should work perfect for retro mod setups where you need to feed the ECM and a old school dash speedo, just match up the correct PPM that works for both units.

Now to set up some cruise control buttons on the boat.

Cheers,

-K

 

Very Nice

 

Here is a quick EFI Live log screenshot from some WOT runs we made in the boat yesterday. As you can see by the green line, this Dakota Digital GPS based VSS signal is very steady. It's mound under 1/2 inch of fiberglass, I was impressed..

-K