Need to get Ford and GM to play nice in the sandbox...need some VSS help please

[kilohertz]

I am now at the point in my '49 F-47 build that I need to get the 2000 ppm pulse signal for the 7747 ECM. I have numerous options and want to use OEM solutions from the JY or what I have on hand, don't want to order from JTR or etc. if I don't have to.

Here's the scenario. 7747 ECM in front of a 1987 Ford AOD from an F-150, and an 8.8 Ford diff from a '93 Explorer. The AOD has both cable for the speedo and electronic VSS output. The diff has the VSS which I think was used for the Ford RABS system as well as VSS. I know GM used a DRAC module which I can get easily from the wreckers and Ford's equivalent was the PSOM. I also have the inline speedo cable VSS from the 80's Ford cars.

I have researched for the last day and can't come up with a definitive answer, I can't find any solid info on what the DRAC can do, input pulses vs output pulses to get to the 2000 ppm. I also can't find any info on the Ford AOD or Diff sensors.

Does anybody here have any experience with the Ford stuff mating with the GM ECM or can help me with determining if the GM DRAC will work with the signals from any of the Ford stuff I have?

Thank you in advance.

Cheers

Here is the inline sensor I have.

17474

[dave w]

The 7747 does not require a VSS input, but the engine runs better with a VSS input. To disable the 7747 VSS input, connect the "PARK" input wire to ground.

The DRAC converts 40 pulses per driveshaft revolutions to 2000 pulses per mile.

Perhaps you can fabricate a 40 tooth trigger wheel? JTR link for driveshaft mounted 40 tooth trigger wheel: https://jagsthatrun.com/collections/speed-sensors/products/differential-mounted-40-tooth-reluctor-ring-for-s10-4l60-e-v8

dave w

[1project2many]

The 7747 wants two 5V pulses per speedometer cable revolution or four A/C voltage pulses per cable revolution. As mentioned, DRAC is designed to convert 40 magnetic pulses into 2 digital pulses. There is a document which explains this: http://gearhead-efi.com/gearhead-efi/doc/DRAC2.pdf There are a number of "divide by" ratios built into the box but the DRAC does not generally work to convert low pulse count speed sensors for 7747.

I would look for a two pulse "Reed style" sensor for your speedometer cable. https://jagsthatrun.com/collections/speed-sensors/products/speed-sensor-place-holder-4pac

[kilohertz]

The 7747 does not require a VSS input, but the engine runs better with a VSS input. To disable the 7747 VSS input, connect the "PARK" input wire to ground.

The DRAC converts 40 pulses per driveshaft revolutions to 2000 pulses per mile.

Perhaps you can fabricate a 40 tooth trigger wheel? JTR link for driveshaft mounted 40 tooth trigger wheel: https://jagsthatrun.com/collections/speed-sensors/products/differential-mounted-40-tooth-reluctor-ring-for-s10-4l60-e-v8

dave w

Thanks Dave,

I am actually using a manual BIN but I still want to use the VSS as I have read about drivability issues, coming to a stop, engine quitting etc. And one day I may want to try HWY cruise mode. What I need to figure out is what does the VSS on the tailshaft of the AOD put out, how many teeth on the ring etc.

1P2M, thanks for the link, will read it shortly, and thanks for the details on what the ECM wants, that helps.

Today I picked up 2 DRACs, one from the 10/95 7427 truck I got the ECM from, and one from a 6396 truck, think it was '90 or 91. I am heading out to the shop to pull the covers off for a look see. I am also going to spin that stand alone inline sensor I have to see how many PPR it puts out.

Thanks for the guidance, I'll continue reading and researching.

Cheers

[tayto]

here i thought you had a 4 speed manual... why are you running a manual bin with an automatic transmission may I ask?

unless you are planning to adapt a 40 tooth reluctor wheel to your output shaft or drive shaft the drac will do nothing for you. it's purpose is to take a 40 pulse per revolution AC signal and converter into a squarewave DC signal for ecu, speedo and cruise control.