I have a 99 f-250 that did have a 5.4L auto trans and im putting a 5.9 12v cummins and nv4500 in it. I bushed a ford oil pressure and coolant temp sensor in to the cummins. I bought a ford cam sensor and had 4 notches machined into harmonic balancer and built a bracket to hold cam sensor. Ok I done this for factory dash tach to work, I would also like a/c clutch to work right.

So what is ford pcm looking for to allow a/c clutch to engage? For tach to work someone told me to ground one wire from cam sensor and hook other wire to aux tach, would hooking cam sensor 1 wire to ground and other wire to both cam sensor pcm input and to aux tach??? That way tach would work and pcm would see engine is running and allow a/c clutch to engage???

 

so no one knows???

 

Your best bet is to call these guys, They do this everyday
http://www.fordcummins.com

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mj, I don't know the answer but, if you want a guess, the 5.4 engine management computer does not "share" circuits in general. Most likely, the tach is driven by an output from the PCM or whatever the 5.4 engine management module is called. One way to get more information is to find a wiring diagram for both the 5.4 Ford and 5.9 Dodge to compare the systems. With the cost of PCM's, an error can be costly!

 

As sparky said get the schematic for the PCM, you need to know whats gets plugged into what spot or you'll might get a little blue smoke for your troubles.
retired electronic tech dealing with aircraft ecu wiring.

 

I got the diagram going to pcm and cant figure out what actually allows pcm to start the a/c clutch.

 

I been getting PRODEMAND wiring diagrams from a friend

 

is the pcm maybe looking for a reading of cam or crank sensor to see engine is running??

 

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