Speed sensor question

[Ludis Langens]

WEG1192 at aol.com wrote:
> 
> Anyone know how to use a stock cruise control speed sensor on a 7747 ECM? I
> am trying to use a Jeep cruise control speed sensor and interface to a 7747.
> I measured an increasing A/C voltage with speed that gave 1.7 VAC at 30 MPH
> with this sensor connected directly to my DVM. I couldn't tell if the
> frequency was varying also, but it probably is. I was told that the TBI ECM
> needs a square wave input. Is there a cheap and dirty circuit that will
> convert this A/C signal to the proper signal without affecting the cruise
> control box?

Any GM vehicle with a C3 ECM and electronically connected speedo will
have the interface circuit you need.  Some vehicles like TBI Camaros or
trucks will have a "4-out buffer" just for this function.  In others,
the circuit might be built into the speedo circuit board.

> I don't care if
> the sensor gives me the right speed, I just need to reset the idle speed
> control logic so my IAC motor will work correctly. If I have a legit TCC
> lockup requirement, I'll spring for the right sensor.

You certainly will care if the IAC reset logic triggers at 7.5 MPH - or
if it requires 120 MPH.

-- 
Ludis Langens                               ludis (at) cruzers (dot) com
Mac, Fiero, & engine controller goodies:  http://www.cruzers.com/~ludis/

----------------------------------------------------------------------------
To unsubscribe from gmecm, send "unsubscribe gmecm" (without the quotes)
in the body of a message (not the subject) to majordomo at lists.diy-efi.org