Engine/Transmission (1994 - 1998) Is the tack run off the alternator?

[Bob V]

The MY96 models were the first year with an identifiable PCM functionality to them that was seprated from the engine controls. The SBEC used on the 94-95 trucks is the same style used on the 89-93 trucks with the same minimal control interfaces. The OD and lockup controls were crude and subject to many issues, more of an after thought than anything. MY96 was the first year for any meaningful PCM functionality to control the 47RE.

The CPS on anything prior to the 24V engine was a simple analog sensor. The signal could not be used by any computerized components because it wasn't digital, it has to be processed first. The CPS sent its signal directly to the SBEC\ECM for conversion then was used to activate the ASD, control the tach, and control the grid heater programming. Works exactly the same way on the newer trucks only the CPS now provides a digital signal with degrees of crank rotation in addition to the rpm. The rpm is a calculation passed to the PCM for it use.

The OP's problem could be sensor, connection, SBEC, or alternator. Only testing will tell.

The CPS/ESS is a discrete signal (on/off) Computers can use analog or discrete (on/off) signals. In reality they ALL end up being discrete- 0s and 1s

 

[SheldonBates]

SMOKIN01CUMMINS,

I hope you will post again and let us know if you were able to find and fix the problem. I would really like to know what the cause of the problem was. Valuable info that would be helpful to me with my ’96 and perhaps others.

 

[Fordpickupman]

It's red.
No.....it's scarlet.

I am working on an early '98 that is suffering from an irradic tach. I would not have thought to check the alternator or the ground. That was a good morsel of information.

 

[HHhuntitall]

And, IIRC, the ESS/CPS share the same ground with the PCM circuit for engergizing the alternator..... A broken CPS ground may still give the tach a signal, but not the PCM. The problem here looks to me to be the CPS, which, when signal is lost to the PCM, makes the alternator stop charging, hence the voltage drop and erratic tach signal..... I would begin with a visual inspection of the CPS, located on top of and slightly to the passenger side of the harmonic dampener on the front of the engine, below the fan support pedestal. I may be damaged, or simply not plugged in correctly. An ohm test of the component could potentially indicate a failure, as well.

And gentlemen, you are most polite in your argument, and all correct in certain points.... I complement your civility.... however, you are not helping the OP in his quest for help...