im using a FAST XFI box in my 95 T/A but im keeping the stock computer to run the gauges and to turn on my fuel pump (external weldon w/controller). what exactly do i have to keep in the wire harness? im worried about the wiring that goes to the transmission (T56) and the coil wire. mostly worried about ignition, for the time being im missing part of the wire harness from fast that adapts from the cam haleffect to the opti wire harenss and i dont want to cut the opti harness off the PCM plugs.

for the most part i have all the sensors and the wires to them cut off, all that remains is the PCM plug-ins, opti wiring, coil wiring, alternator wiring for gauge, tranny wiring and a few connectors that have not been sorted out yet.

in the future im going to convert to all after market gauges and killing the computer all together so if there was a way to wire up the ignition w/o the computer let me know.

if someone could shine some light on this it would save me from blowing my car up thanks.

if this is not tech enough to belong here im sorry i just figured it would be the best place.

 

this isnt looking too good.... i hope someone on here can tell me something.

 

I will probably burst into flames for posting this..but I don't think any sponsoring vendors have a solution.

Give this turkey a call. Ask for Brian.
http://www.horsepowerconnection.com/

Thanks
Dennis

 

every time i try that site it pisses my computer off for some reason.

 

The fuel pump will not work the way you have it set up. When the opti spark is disconnected from the car the fuel pump will not run. The XFI will control your fuel pump. Also, the only gauges that will work are water temp, fuel level, oil pres, and spedo. The factory tach will not work, and unless you like the check engine light I would remove the bulb. The way I did it was to keep the original harness in place, and simply cut the wires behind the ECU. Then I made a short harness to connect to the factory wires. This will save a bunch of time (assuming you don't have the XFI harness). I am running a classic bank to bank system, I am sure there are some differences with the XFI. If you get confused try to find a pin out for the XFI (tech support can give you this, unless it's already in the help feature). I hope this info helps you along.

Good Luck
Aleks

 

i have the xfi wire harness so i just removed all the wires from my stock wire harness that i dont need anymore such at all the sensors that the XFI harness has and all my a/c stuff and emissions junk.

so if i just hook the xfi fuel pump wire up the the relay like it says in the instructions i should be good right? or so i still need to run more wires to that relay? this would be sooooo much easier if i had an real schematic that went into detail including inside the PCM.

thanks for the the help.

 

Yup. I would follow the instructions .
You can get a terminal removal kit and back the wires out of the stock ECU clips. This way you never have to cut anything, and if you change your mind you can easily put the stock system back.

 

too late i cut that bastard to pieces... lol

just for future reference is there any way to run my coil w/o using the computer. on the ignition coil module there is a wire (white) that runs to the PCM what does it do? if its just to power the ICM then that should be a easy fix. any help would be appreciated.

 

The white wire from the stock PCM to the IC Module tells the system when to fire. You should be getting the ignition timing info from the XFI, if you are feeding the XFI with a Hall effect cam position sensor. Your stock PCM can't handle the ignition or the injectors without the Opti optical sensor signals.

You don't need the stock PCM, or any PCM for the coolant temp, oil pressure, fuel level and volt meter gauges. They are all wired directily, not through the PCM. You only need the stock PCM for the speedo, and you could probably find a work around for that using the interfaces available from Dakota Digital.

I still have the stock PCM for the speedo, fuel pump control and IAC control. The version of the MoTeC ECU that I have can not control the GM stepper type IAC motor. But it can accept the Opti signals, so I have the Opti paralleled into both ECU's. That keeps the fuel pump control in the stock PCM.

I'm guessing you didn't get more than a couple responses because its not really an "Advanced Tech" problem as much at a "Computer......" problem. I'll try moving it to "Computer......" forum.

 

Try these guys:

http://members.aol.com/bigturbo1/plugplay.html

They have a plug and play harness for LT1's and FAST boxes (not sure on the XFI boxes). Its a direct plug and play setup... not cutting or splicing.

 

Damn I wish I would've seen this sooner, probably could've saved you a headache or two.

My tach works so for the other guy saying it won't I can't explain that for you. Fuel pump is controlled by the stk pcm and that's it. Everything else is wired into the XFI...IAC, TPS, MAP, Coolant, fans, ignition etc. T56 and fuel pump is still hooked up to the factory pcm. All my gauges work too and the SES will trigger on the dash as well as in the XFI. You can try a white racing harness but I got my harness from Brian Macy at Horsepower connections pretty straight forward too. If you want I can scan the instructions and email it to you tomorrow so you know exactly what is done.


Silas,

 

It all makes sense now....
I am using a monster tach
Also, I talked with my wiring expert. He confirmed that I was wrong. My F.A.S.T. is piggy backed on my stock ECU. The stock ECU is running the FP.

Sorry for the bad info

I confused my car harness with my dyno harness. I was using the dyno harness on an engine that was in a car. That's why the opti was unplugged from the stock ecu. I had to make a jumper wire for the fuel pump relay to get the pump to kick on.

 

so basically if im willing to not have a speedo and wire my fuel system myself i can take stock computer and toss it huh? im still waiting for my halleffect to opti wire that i was missing from fast so when it gets here and i can get rid of the stocker than its history... i can live w/o a speedo for a lil bit.

thanks for the help guys

 

oh yea...

what was killing me the entire time was the crappy schematic i have that shows everything going into the PCM it doesnt distinguish between PCM and the white,black and blue plug ins under the dash

 

All my factory gauges work, tach, speedo etc...all of it. XFI is only controlling the spark, fuel, fans, tps, iac, map, iat, ses, etc.