VSS question...

I have the 7747 ECM set up, and am close to finishing up this never ending project I hope. My question is, what issue will the lack of VSS do as far as tuning? I havbe a 700r trans, but it is set up with a pressure switch conversion to control the shift points, and the converter lock up is done like this as well, with the lock up working off the brake switch. (Street rod conversion I guess). I had this same set up in a v8 s10 blazer with a 327 and LUV'd it, but the engine was carbed on that one. Trans has a mechanical speedo if that makes any difference. Thanks.

Working from memory, I recall people having high-idle problems as a result of omitting VSS.
I believe that the vehicle speed is used in calcs for EGR operation, decel fuel cutoff, power enrichment.
Mike V

I am.hoping there is a work arpund as the big block trucks had a turbo 400...

The old-time swapper place; "Jags That Run" has a number of solutions.
Do you have a speedometer cable drive on that trans?
http://www.jagsthatrun.com/Pages/Spe...eedometer.html

Mike V

Yes, I have adapted the factory nissan cable with a chevy end to operate the factory speedometer...

It looks like most of their VSS solutions are $100 or less. A phone call might be the best way to get the right part.
They have adapters that pass the mechanical rotation through to your speedometer cable and give you a VSS
signal in addition. If anyone can come up with what you need, my bet would be on them.

Thanks for the info...

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Originally Posted by mytmouz

I have the 7747 ECM set up, and am close to finishing up this never ending project I hope. My question is, what issue will the lack of VSS do as far as tuning? I havbe a 700r trans, but it is set up with a pressure switch conversion to control the shift points, and the converter lock up is done like this as well, with the lock up working off the brake switch. (Street rod conversion I guess). I had this same set up in a v8 s10 blazer with a 327 and LUV'd it, but the engine was carbed on that one. Trans has a mechanical speedo if that makes any difference. Thanks.

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Don't know specifically abouit the '7747, but do know that many of the GM ECMs (ie - 7730) use many tests in the code using VSS data. The critical issue is idle. Idle is determiined in most of the ECMs as TPS% <= 0.78% and VSS = 0. Ditto the opposite for not idling and many tests there also. So if VSS is not installed, code tests of VSS status are indeterminate.

Ok, after looking, I did not remove the vss wiring from the harness. I have converted the trans back to the stock 4 pin connector and internal harness. I am now trying to check the wiring to see if it is connected every where. What I need is some verification help. I see the A pin on the 4 pin connector goes to one side of the brake switch. Open or closed side? B pin to C7, none on C, and D to A7 and the ALDL port. Sound right? Next is the 2 VSS wires. I plan on getting the JTR adapter that has two wires and the mechanical speedo. I have the VSS Brown wire going to A10. The purple wire is the one I am having trouble figuring out. Seems like the schematic here shows a permanent magnet motor? Another schematic seems to show it on the a side of the brake switch? Open or closed? I have no clue... Thanks

So, after researching some, I believe with the JTR adapter Speed Sensor, # 2PRS, I will just connect the two wires to that unit, and the other ends of those twisted wires to A10 the purple wire, and A12, a ground.. Which is good, since they currently are not connected after leaving a plug in the harness. None of the dash wiring was with the harness I got so anything it connected to I don't have...

Verifed the 4 pin wiring, All connected except for the wire to the brake switch. Believe it should be on the open side of the switch to operate the lock up. Does this sound right? Thanks.

I'd have to look at diagrams to be sure but IIRC it always has power and when brake is applied it looses power so TCC unlocks.

That is how I have it wired. Hopefully I am close to finishing it up after all these years, lol...

More VSS info that may be helpful.