12v to 99 sd swap tach?

destroked 99

destroked 99

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May 1, 2011
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Ok just about to start tying up loose ends on my swap. One issue is making my tach work with a fluidamper! Truck is a 99 f250 5.4 truck. Im not soo much worried about the tach as being sure my a/c will still cycle as it should. Will the dakota digital flywheel setup work? I know i can run an aftermarket tach with it but dont know how the ecm will work with it. I would appreciate any advice/help!

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in a 99-01 you have to bybass the ecm to make the tach work,which means the a/c will not work. easy fix-pull the a/c harness off the fenderwell and connect the gray wire from the compressor plug to white/green stripe wire from the high pressure switch. this will bypass the ecm for the a/c and it will still cycle like normal.

wire colors are as follows-

purple-power from incab switch. goes to low pressure switch
red w/yellow stripe-comes from low pressure,goes to high pressure
white w/green stripe-high pressure to pcm.
grey-a/c compressor power
black-a/c compressor ground
 
Thank you sir!!
Has anyone hooked up the factory tach with say a dakota digital flywheel pickup, or some other means of getting a tach signal?

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so from what your saying you have to bypass the ecm to get the tach to work then the ac wont work? Cause I have my ac going but I am about maybe hook up my tach some day. rileydsking so the tach dont go through the ecm? do you know if i could use a fryed up 7.3 ecm? Im not trying to jack the thread

Destroked99 how do you like your swap so far?
 
That is not true. The 99-01 SD do not use the PCM it is a direct control from the climate control switches.
 
Freds99: im just abouth through with it, havent even fired it off yet tho. Wanted to get almost everything done before i started it.

As of right now i HATE the moneypit!! Lol . It has been a long project that started as a simple swap, and ended up being a full engine build from bottom to top, redid the interior, a bunch of time and money! I need to start posting some pics, just kind of wanted to be done before i did.

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O I for sure understand the money pit and thinking it would be a simple swap lol
 
Mo Smoke said:
That is not true. The 99-01 SD do not use the PCM it is a direct control from the climate control switches.
Click to expand...

i know you have a lot of experince on these swaps, what would be the reason mine would not work after the swap unless i ran the compressor power from the high pressure switch?
 
It actually does, Power is provided through the a/c selector in cab then through the Low pressure switch then th High pressure switch then to the Comp coil. Email me your addy and I will send you the service man wiring diag later today.
 
Hey mo smoke do you know if I could use a fryed ECM would it still let the tach work?
 
On mine the ECM controled the compressor relay. On my tach I ran stright to the tach wire going to the cluster. It works but I'm going to change it. I would find a way to run the tach threw your ECM it'll make things a lot easier in the long run. IMO
 
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