Running a FAST standalone vs piggybacking stock computer

looking from some help from the big dogs running standalone systems

How many people here have gotten rid of the stock pcm/ecm completely and replaced it totally with a FAST computer? and how many have used it to piggyback with the stock computer?

What are the pro's and con's of each?
what will and wont function if i ditch the factory computer all together.
im not worried about a/c, air pump, emissions, foglights, horns, airbag sensors.
I am only concerned with what i need to keep to make the car run and drive Will the factory guages not work with just the FAST?
what wiring can i completely ditch and is unneeded

I had planed on ditching the stock computer all together and only running the original FAST with msd digital 6, hvc II coil, conventional rear mounted dist., and a msd crank trigger setup.

Im all ears to any and everything i need to know on the subject of standalone vs piggybacking the FAST.


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The factory ECU runs your speedo and filters the tach signal. All the other gauges will work with some re-wiring. My tach works, but not correctly and could probably be fixed with a filter of some sort.

The pro's are obvious if you've ever tried to work with the stock ECU. The cons are really just the stock gauges. But you can always replace them with autometers.

The fast system comes with a harness to use on the engine... So I simply removed the sensor wiring from my stock harness and made my own simple harness for coolant temp and the altenator signal for the charge indicator. There's nothing else needed out of the stock engine harness for the gauges to work.

Thanks alot bud, I was waiting for you to chime in, you always seem to help when it come to the fast stuff

Quote:

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Originally Posted by Fire67

The factory ECU runs your speedo and filters the tach signal. All the other gauges will work with some re-wiring. My tach works, but not correctly and could probably be fixed with a filter of some sort.

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I am using the factory ECU for the speedo, A/C, fuel pump relay, and cruise control. I am using the factory tach and it works perfectly (honestly I can't recall how we go it to work right now I believe it's wired in with the MSD Dig 6). Everything else is controlled with the DFI. I do consider my car more street than race so that is why I choose to keep the CC and AC. My bet is most running an aftermarket fuel injection have ditched everything except maybe the speedo.

Basically if you are set on keeping the factory speedo working then I think you need to piggyback the two.

You can run the stock ecu with the FAST system, but the wiring gets quite a bit more involved. You are basically gonna take the engine controls and sensors away from the stock ECU. With the exception of the wiring to the ignition system, IIRC you will have to share the wire that supplies rpm info to both ECU's. OR pull the rpm signal from an MSD box to feed the FAST and leave the rpm signal for the stock ECU untouched.