I am working with a truck that has a 365 (started as a 348, same design as a 409, yes W-head and all), in a 1967 GMC pick. Custom MPFI intake, 17.2 Lbs/hr injectors (for now), TH400, 7747 ECM. TP RT/ Ostrich 2.0/ Home made serial ALDL cable/ Bin I don't recall(I can look it up if needed)/ 7747_mine.XDF

What we need to do is hook up the VSS, he has an aftermarket VSS that screws onto the speedo cable output and has two wires, I believe it is a magnetic sensor.

What I am wondering is, if I ground one wire from the sensor and then connect the other wire to the VSS input into the ECM, will that work? I haven't looked at the Bin/xdf to see what variables if any would or could be changed to compensate for any errors from this.

Or will I need a DRAC module (IIRC that is what the later 1st gen S-series used for the VSS)?

TIA

 

I don'tknow the answer to your question but there's a bunch of info here.

https://shell7.tdl.com/~jags/V8-chap...ed-Sensors.pdf

 

If its from JTR 2000 ppm unit - its magnetic interrupter switch - it should work as you have outlined. No DRAC is needed.

//RF

 

Thanks, that's good info, and will most likely come in handy.
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Yeah I'll have to find out exactly what he bought. After reading through the long Binder provided it gave me hope that I may be able to keep this simple.

 

It was RF that pointed out JTR to me last week.

 

I found out yesterday that it is a Painless VSS, I'll try and find teh specs on it.

I connected it, one terminal to ground (at the ECM) the other to the VSS input (had to add a pin for some reason), and it "works", but the speed is WAY off. While the speedo shows about 40 MPH, the ECM showed 75 to 80 MPH or so, and would spike high (about 150 MPH or so) ever now and then.
It would show 0 MPH before being stopped.

SO I'm thinking that a DRAC module is needed, or could I simply change something in the bin to compensate?

 

Well I think I found it, he said there was a "1 and a 6" in the part number, he didn't have the packaging anymore.

According to the Painless EFI accessories page that would be a 4 pulse VSS, and would explain the high (by about double) the MPH on the ALDL dash. From the above article that would also indicate this is also a sine wave generator or should be, due to the 4 pulse sensors being this stock. The part number 60115 would be an exact match, would it not?

I think I can use his VSS for my conversion though, since I'm not sure if the custom made (adapted) one on my truck ever really read correctly. I have a 7730 in there now running $8d IIRC (MPFI V6), but am looking to run a 7749, with $59, when I get it back out.

 

To use a 4-pole mag VSS on the TBI setup you need to get a 4-out buffer box. They are on a bunch of GM vehicles: '86-'90 MAF f-body's with a non-cable speedo (Firebirds got them first), all of the f-body TBI cars, and the Caprices in the '87-'91 MY range. It is a white or yellow plastic box with a paper label with '4-OUT BUFFER' on it. Found on passenger side along the lower edge of the dash.

The Lumina and Transport TBI vans ('91 - '93 or so), also have a 4-out buffer box. Although in this case it is a smaller version of it. But works the same and is mounted with the ECM.

For a '7730, '7749, the ECM will act as the 4-out buffer box.

RBob.