Can anyone tell me what all you need the stock pcm for after you get an aftermarket engine management system?

I want to get a FAST computer for my 94 Z28. It doesn't have heat or A/C. I was wondering what can be done to handle things like the lights and gauges? I'm pretty sure the FAST system can run a tach, but what about the speedo, temp, oil pressure, and gas gauges?

Any info would be appreciated.

Jeremy

 

I'm in the same boat as you, been playing with the idea of an aftermarket system but dunno what to do bout gauges and such.

From what I've read most people have to keep their stock computer in place to use most of those things. I dunno if theres another way around it, hopefully someone else will give a better answer to this.

Also what type of sensor are people using in place of the opti sensor? I've seen some pics of a couple motors that did away with the opti and didn't know what kind of sensor they were using for their setups.

 

The dash gauges - oil pressure, coolant temp, fuel level and alternator voltage - are not connected to or driven by the stock PCM. They will work fine without the PCM.

The tach and speedo are driven off the stock PCM. I would think virtually any aftermarket ECU would drive the tach. And with the limited range of the stock tach, not sure if you would even use it for a high revving engine - I run an AutoMeter tach for the 7,000+RPM capability, and as an aide to "senior citizen" eyesight .

The speedo can be driven off the stock PCM (that's how I run mine) or you may be able to interface the VSS output directly to the speedo with the Dakota Digital speedo box.

I use the stock PCM for IAC control, since my MoTeC will not interface with the GM "stepper" IAC motor. It will only drive a pulse width modulated valve (at least the older version I have, the new MoTeCs will interface with the GM IAC). I also kept all the emissions stuff working for a while, until it became a track car and didn't have to pass rolling emissions testing. And I run the fans off the stock PCM.

You would have to find another way to power the fuel pump if you delete the stock PCM, or if you don't keep the Opti optical output. The stock PCM provides the fuel pump signal. It needs the Opti low res pulse, or it will not keep the pump running. Not hard to get around. I still run the fuel pump off the stock PCM, but I have the Opti in place, using the stock optical sensor as a cam position sensor to feed the MoTeC. I believe FAST also offers an option to use the Opti optical sensor signals as the cam reference signal. You only need that if you run sequential injection. If you choose bank-to-bank, you don't need a cam reference signal.

I also believe (not positive though) you can do an 8-coil direct fire ignition with the FAST if you add the eDist and keep the Opti low res pulse, or an equivalent cam reference signal. I run the 8-coil setup using the MoTeC IEX 8-channel ignition driver.

 

Thanks Injuneer, thats good info.

I was just going to upgrade to the MSD opti, to avoid some of those problems. Has anyone heard any good or bad things about it?

I'm pretty sure the new FAST XFI can run the fans and fuel pump, and to tell you the truth the speedo isn't really that important, for now anyway.

I'm not sure what I want to do about emissions equipment though, I probably won't run any of it.

I'm really not going to turn the motor that high, maybe 7000rpm, give or take a few hundred. Is there really any advantage to running an 8 coil system?

Thanks,
Jeremy

 

8 coils have 8X as much time to recharge before they need to fire again.... valuable at higher RPM.

Here's an engine running 8 coils on an aftermarket Gen 1 SBC, and it uses a magnet on the cam sprocket and sensor in the timing cover to generate the cam reference signal. MoTeC/IEX setup:

http://www.injuneer.com/images/photo.../DCP03825a.jpg

What MSD box are you asking about.... the CPC system, or one of the "6" series boxes?

 

Not really sure what you mean? I was thinking about using the MSD version of the optispark, with a 6AL box for more spark. I don't know a whole lot about there other products, specifically the multiple coil systems.