1984 Coupe - ECM Bypass

[AussieCorvetteNut]

Hi Guys,

I am thinking of eliminating my ECM in my 84 as part of my FAST EZ EFI Engine Management Upgrade, that will power my Edelbrock PRO FLO XT.

Just wondering if anyone has removed the ECM from their Vette.

I have started to eliminate Crossfire Injection wiring and 4+3 wiring as I am also installing a Tremec TKO 600.

I have disconnected the ECM Plugs, marked the wires, but am thinking I can eleimnate the ECM altogether, besides, I need the room to run the FAST ECM and FAST Ignition System.

I know the digital dash runs on its own and is separate from the ECM.

Any thoughts?

Thanks Tony

 

[DaveP85C4]

The instant MPG, avg MPG, miles to empty, etc computations won't work. You will also need stand-alone cooling fan control. Maybe FAST can do that. I don't recall. I don't recall if the A/C clutch control in an 84 is by the ECM or not. This is easy to work around if it is.

Not all the wires in the engine harness are for ECM controlled systems. You can't remove the entire harness. Well yes you can, but there's some circuits you have to re establish. Like start and charge, primary ignition, IP gauges.

 

[AussieCorvetteNut]

Thanks Dave

The instant MPG, avg MPG, miles to empty, etc computations won't work. You will also need stand-alone cooling fan control. Maybe FAST can do that. I don't recall. I don't recall if the A/C clutch control in an 84 is by the ECM or not. This is easy to work around if it is.

Not all the wires in the engine harness are for ECM controlled systems. You can't remove the entire harness. Well yes you can, but there's some circuits you have to re establish. Like start and charge, primary ignition, IP gauges.

Thanks Dave.

I am not too worried about instant MPG and AVG MPG and distance to empty, I took a look at the Electrical Diagrams after I posted and also found that it said that the ECM controls the calculations for these displays, but that these are the only thing the ECM influences on the guages.
They are the only ones I can find as well.
Do you know if anything will light up in the centre IP that is controlled by the ECM, if there are no signals from the ECM?


The FAST ECM controls cooling fans, you can set up the temperature you want the fans to kick in and when they shut off. This is done with the colour display pad.
I don't really want to mount this in a visible location like where most people mount their aftermarket GPS units. Some clown may think it is a GPS and knock it off.
The FAST system doesn't require the display to be connected after set up, but it does provide instant analysis....and from memory it isn't cheap to replace.

A/C Clutch control...mmmm I will check this out.

I was thinking about re-using the harness, but just disconnecting and removing the ECM. I have this harness out and it is resting over the front windshield while I work through it.
I have pulled the harnesses in the engine bay apart (front lights harness), as the plastic conduit and the harness tape has 30 years of oil soak, dirt and crap, and the conduit was brittle in a few places.

The old harness will be re-wrapped and conduit replaced and I will route the new harnesses for the FAST EFI and the DeWitts Spal Fan kit in with the harness and just tidy it up.
The non-adhesive harness tape arrived this week.

I am unsure where to run the E6 Ignition Box, if I mount in the passenger compartment, then I have to run power and earth direct from the battery through the firewall and then it has a harness that runs back to the coil pack.
Real estate is becoming an issue.

I can do most of the wire tidy up and install, but I am thinking on getting a sparky out when it comes to the ignition and charging circuits.
My fuse panel needs a tidy up after 30 years of bastardization, so I want to clean all this up and have reliable connections here.

Any tips or advice are welcomed.

Regards Tony

 

[DaveP85C4]

Tony:

Nothing in the centre DIC is ECM derived. Well, Service Engine Soon is....

My primary advise is to "think of everything" you want to incorporate into your harness and system. If you forget something, and have the new loom completed, it's tough to add a wire. I am currently doing a Holley Dominator system into a 91 GMC Syclone. I have pretty much started from scratch on the firewall side of the harness. The changes to the Instrument Panel side were extensive. I added another fuse centre to handle the Power Distribution to the pumps, electric fans, etc. Very extensive.

I had the IP harness completed, and the owner and I were going through his stuff for the truck, and I spotted a transmission temp gauge. I had to add the wire for the gauge sender. He also relocated the battery to the bed. While I knew about this, but forgot that SCCA requires a battery cutoff switch mounted on the rear, and that the switch must kill the running engine during tech. I had to add wires for the alternator cut. I had the IP harness completed, but only tie-wrapped. It wasn't difficult to add the changes, only a bunch of tie wraps.

So my suggestion from this experience is to bundle the new harnesses with tie wraps as you work on the fabrication. Don't do the final taping and looming until you're satisfied that you've "though of everything".


I've dated a Kiwi, and have had a lot of exposure to Aussie and Kiwi-talk because of my interaction with other sailors and yachties over the years, but I've never heard the term "getting a sparkie out". Enlighten me please.... Edit: I re-read your post and put this in context. I think "a sparkie" is an "electrician"? Cool.

Here's the Syclone IP harness:

 

[AussieCorvetteNut]

"get a sparky out'

Hi Dave,

'Get a sparky out' is just calling a mobile auto-electrician to come out.
When you look at my fuse panel, it isn't pretty and there are pink/black wires all piggy-backing off each other...a mess and probably a fire waiting to happen...its amazing it doesn't pop fuses!
The Vette has had a RH Drive conversion, but the conversion guys (who did the conversion 20 years ago), would not have left this a mess, it has been others since.
My concerns are the ignition and charging circuits.

I laughed when you said that you dated a Kiwi...I am married to a Kiwi Girl!


All makes sense Dave, I am working through what goes where and I will grab some zip-ties and do a wiring harness mock-up like you have done...nice work!
I am in the middle of spray painting the inner guards, wheel well guards and spare tyre holder, will paint this Friday Morning early...2-pac satin black...should look good...I know its Easter (Good Friday), but its 4 days in the shed!
Once this is done, I have something to hold the harness as I add to it.

I need to 'bite the bullet' and mount the FAST E6 Ignition Box and FAST ECM...it also adds to the harness.
Both units come with a small amount of harness, but I may need to extend these...FAST recommends that the E6 Ignition box be mounted inside the cabin, or if in the engine bay, away from direct water...not enough harness supplied.
The ECU displays lights, so I would like to put it down under the dash where you could see it if you looked under the steering wheel...not sure real estate is an issue in a Vette.
The colour touchpad mounts like an after-market GPS unit.

I am having problems locating a serpentine accessory drive system. I am fitting an Edelbrock PRO FLO XT intake with LS1/LS2 90mm throttle body, so I need to change my serpentine system, am looking at one GM Performance Parts has, but it has a long water pump...it won't fit Corvette, Vettes have short water pumps.
I will have to source a complete unit from a 85 to 87 Vette donor car to suit TPI as the TPI Vettes have the same intake profile, with a front mount throttle body, same as the unit I am installing...only the 90mm throttle body and intake will flow at 1000 cfm unlike a TPI unit!
The FAST Mutlipoint Kit (30404) and harness will manage this intake, still working on what injectors to run, I have installed an 85 to 87 Corvette Fuel Sender and Pump, I should be right with the pump...injectors need to be around 32 to 36 PSI...if the FAST Diagnostic says there is not enough fuel pressure, then I will change the pump.
Throttle cable is now an issue...I purchased a Lokar unit...nup no good at the pedal end.

All fun and games when you re-invent the wheel!



Tony