I am plnning on converting to a carb this winter and I am going to remove the ECM and harness if I can. I wanted to know what all my ecm controls. It might be easier to ask what it does not control. I have a 4th gear lockup only kit so the ECM does not control that anymore. But, all I need is the gauges, fuel pump(I am leaving the electric pump for now), windows(I am pretty sure they are not but I need to ask), lights(also pretty sure they do not). Also, how do I hook up the tach to a vacuum advance dizzy(what color wire). The main thing I need is the speedo. If it will not work without the ECM, how can I make it work. Thanks

 

Lights, windows, and all that are not tied to the ECM. As for the speedo, look under the dash for a yellow or white box that is labeled 4-OUT BUFFER. If you have that (I believe the car should), the speedo is good to go. If no box, need to get one and install it.

Fuel pump relay is run by the ECM. There is also an oil pressure backup switch that will also power the pump (oil pressure needs to be above 4 psi to operate the FP).

Can run the fuel pump relay enable to an ignition switched 12v source. This is the same relay terminal that used to go to the ECM.

Tach wire gets hooked to coil minus.

RBob.

 

Thanks for the reply. That is what I have been told, but it is hard to believe someone off of the street. I figured none of the windows or lights run off of it but you know how stupid somethings are that GM does. As for the fuel pump relay and oil pressure switch, I need to find the wire that goes to the ECM and run 12v to that? Thanks again.

 

I just thought of something, does the GTA have a digital dash? I think that they may use a data stream from the ECM. Not sure though.

RBob.

 

No, it does not have the digital dash. Thanks

 

since you don't have the digital dash, you're good to go. As stated, just make sure you have the VSS buffer box. - it has a wire running to the computer, but just cut it.

 

Okay, so here is my next question. If I unhook my cruise control will it effect my speedo like it does on a cable driven setup or will I be okay. Thanks

 

Not to beat a dead horse, but I'm going through the same thing and have some possibly dumb questions....

Doesn't the fuel pump issue depend on the year and configuration? Mine is an '86 with the LG4 with a quadrajet. It clearly has a mechanical fuel pump at the block. Doesn't that mean I do not have an electric one in the tank? For instance, if you go to Autozone and ask for a fuel pump for an LG4 "H" code with quadrajet, they don't ask which one, they only show a mechanical. So when I ditch the ECM, I'm assuming the fuel pump will be no issue.

Re: the speedo. Rob, are you saying if I have the yellow box, just cut the wire between the box and the ECM and my speedo will work fine?

What about the A/C? If I ditch the ECM, will I lose the A/C?

I'd also like to know about the cruise issue.

I assume I have the lock up convertor. I know I can get a lock-up kit, but what if I don't? What will happen? Will it just not luck-up? I always hated the lock-up convertor. Can't I just live without it?

I appreciate any help. I'm deep in the middle of all this and appreciate any advice. As of now, the carb, intake, exhaust manifiolds, radiator and all accessories have been removed. I've got a mild cam on the way, and I have a 2101 performer intake, 1901 Q-jet, MSD digital e distributor, Stewart water pump, SLP headers, and firehawk exhaust waiting to go back.

I've resisted just taking aviator snips and cutting out the ugly wiring under the hood but am holding off until I'm sure of what I need to keep.

This forum has already been a fabulous source for me since I got this car a few months ago. Thanks for the past and future help.

 

Your A/C will work w/o the ecm. the ecm has nothing to do w/ the a/c other than it needs to know when you turn the a/c on(to adjust air/fuel, idle rpms,etc..). - If you have a factory carb/mechanical pump motor, you're good to go on the fuel system. - If you have an in-tank electric, you'll not only have to trigger the relay, you'll have to put in a regulator, as even a tbi pump makes too much pressure for carb needle and seat. Tach wire is a small white wire hooking to the coil...if you don't lock the converter up on a 700r4 during highway/extended continous driving(not stop and go) you'll burn the transmission up. If you want to go non-lock up, you'll need a transmission and converter built for it. What's wrong w/ a lock-up converter? It can only help you. The factory ecm doesn't really control it for crap(early lock-ups, continual locking and unlocking), but properly functioning, it's a great thing...

 

the big fat harness that runs into the passenger side cowl/fener is the ECM harness, for the carb and hei and emissions equipment only

the entire harness will come out of the car one one piece real easy after you unplug it off the carb and HEI and knock sensor and MAP sensor and 02 sensor and TVS's in the intake and such and when you put non CCC HEI and carb on it will fire up and run jut fine without the entire harness

it has non of the starter or alt or HEI BATT wire or temperature wire stuff in it

nor anything inside the car, or lights or anything on the body of the car



but does have the converter lockup wires in it


the 86 LG4 would only have mechnical pump on the block

some L69 had an electric pump in the tank though along with the pump on the block too


you only have the one on the block if its LG4

good luck

 

Thanks, **** and fast68. I appreciate the info. I've progressed to a complete rebuild of the motor. Got it out and down to the bare block. All the info you've given is exactly what I'm looking for. What a great forum!

****, I'm sure you're right about the lock-up. I'll get the kit. Back in the '80s when they first started putting them in, they were real klunky and seemed to be a drag on the drivetrain. I'm too old school sometimes in my thinking.

Thanks again for all the help. Any other thoughts, tips or warnings are appreciated.

 

Doesn't the ECM control the compressor clutch relay? I know it doesn't take pressure switch inputs but at least on my Caprice, I think the ECM delays the compressor clutch relay from engaging until the IAC has had time to affect the idle speed.