16197427 PCM info

[Shannen Durphey]

WEG1192 at aol.com wrote:
> 
> I have found out some interesting info for those using a 16197427 PCM (194-95
> TBI PCM). According to Jagsthatrun, you need a 40 reluctor ring type speed
> sensor in the tranny for this PCM to get a speed signal.  But on a hunch, I
> ran one with a JTR 4 pulse per rev magnetic speed sensor and got a reading
> double my actual speed. Also, I got no reading at all until about 45 MPH and
> up, and an erratic one at that. So, knowing that the 2000 PPM speed sensor
> was an optical one and not a magnetic and that it would give me half the
> pulses, I tried the 2000 PPM on the 16197427 and it works perfectly.
> Apparently the 40 tooth speed sensor goes to a DRAC which then sends a 2000
> PPM signal to the PCM. 

Isn't this stated in the DRAC document?  The whole point of the divide ratio is
to convert the 40 pulse per driveshaft revolution signal into a 2000 pulse per
mile signal for the ecm/pcm.  If the vehicle has a DRAC, the controller expects
a 2k or 4k pulse/mile signal.

> This means you don't need  the DRAC at all and can run
> a cable driven speed sensor directly into the later model  PCM.

Along with the optical sensor, a reed type aftermarket speed sensor will provide
the appropriate signal.

Be aware that the 7427 expects to see input and output shaft speed signals for
4L80E applications.  I can dig out the number of teeth on these sensors if
needed.  I believe these are less than 40 pulse/revolution sensors.

Shannen

> 
> Now, why would you want to do that you ask? So that you can use Datamaster
> with a P4 PCM and get some high speed data for tuning a TBI system. Problem
> is, even with a working speed sensor, I can't get the BLM (LT Counts) to move
> off 128. The Integrator  (ST counts) moves as it should and is correcting the
> AFR in closed loop, but my BLMs stay locked at 128 for a full 20 minute
> drive. The fuel trim cell #s shift around as well. Anyone know what could be
> keeping the BLM locked at 128?
> 
> Thanks,
> JW
> ----------------------------------------------------------------------------
> 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
----------------------------------------------------------------------------
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