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DFI and ECM Discuss all aspects of DFI (Digital Fuel Injection), ECMs (Electronic Control Module), scanners, and diagnostic equipment. Fine tune your Third Gen computer system for top performance.

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Old 04-26-2008, 09:10 PM   #1
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What does the ECM do on an 85 LG4

I was under the dash of my car today lookin at the cruise control module, and i saw that the computer wasnt plugged in. so i looked around for the connectors, but they were no where to be found.

the computer was jsut sitting there, mounted perfectly... not plugged in...

so, i know the computer is there for a reason or it woudlnt be there.

The car runs great, always has. So what is the purpose for the computer.

Its a canadian car, so it DOES NOT have the computer controlled quadrajet, it has just a normal quadra-jet.

So what does the computer do... Why cant i find the wires?...Would anythgint work better if i plugged it in (if i found the wires)
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Old 04-26-2008, 09:49 PM   #2
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Re: What does the ECM do on an 85 LG4

I'm going to watch this thread because I was wondering that and I also have the same year and same engine, though mine's a US one. Haven't had it long enough to look at everything that's connected. Carb, distributor, I think the egr. I might just remove all of it since the engine's bad and I'm putting in my 350 block.
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Old 04-27-2008, 01:23 AM   #3
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Re: What does the ECM do on an 85 LG4

There was another thread on here that I was reading...not sure what forum, maybe the History/Restoration forum. Anyway, something similar came up about Canadian cars that didn't have a computer controlled carb. Apparently the cars in Canada got these carbs, and therefore didn't use the ECM...but US cars did have the computer controlled carb and the ECM. As far as them not being computer controlled, but still having the ECM...I have no idea why. I'm pretty sure it was a Canada only thing.

Here is the thread:http://www.thirdgen.org/techboard/hi...here-ever.html

Last edited by 1982TA; 04-27-2008 at 01:44 AM.
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Old 05-07-2008, 04:57 PM   #4
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Re: What does the ECM do on an 85 LG4

It's pretty basic engine control, honestly I wouldn't bother if the car runs well. Off the top of my head, the LG4 ECM mainly controls fuel, spark advance, and torque converter lockup (700R4). It has a coolant temp sensor in the water neck, a map sensor on the firewall (I think), O2 sensor, TPS mounted in the carb, and a VSS on the back of the gauge cluster. Fuel metering is done by controlling the primary metering rods in the carb. It's a pretty simple setup, but definitely not the most efficient system in the world.
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Old 05-07-2008, 05:28 PM   #5
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Re: What does the ECM do on an 85 LG4

Oh my lord. THe computer controls the timing, which is super important. If you are going to keep the electronically controlle distributor (assuming it has not already been swapped out with a regular HEI), you need to get the ECU back up and running. You are wasting a ton of fuel, and losing a ton of power, with it disconnected.
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Old 05-07-2008, 05:52 PM   #6
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Re: What does the ECM do on an 85 LG4

I bet the distributor was swapped out to mechanical?
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Old 05-07-2008, 08:18 PM   #7
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Re: What does the ECM do on an 85 LG4

You guys dont understand, canadian LG4's always had mechanical distrib's and carb's.

I've done research and found out that the canadian LG4's never used a computer (hence no wires) Why its in there. no idea...
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Old 05-07-2008, 09:13 PM   #8
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Re: What does the ECM do on an 85 LG4

Just out of curiosity, how is the torque converter lockup controlled on the canadian models? Normally the ECM does it, based on RPM and VSS input.
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Old 05-07-2008, 09:58 PM   #9
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Re: What does the ECM do on an 85 LG4

I dont have the slightest idea, I thought there was no such thing as a computer controlled 700R4 :S
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Old 05-07-2008, 10:17 PM   #10
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Re: What does the ECM do on an 85 LG4

Quote:
Originally Posted by Tehsocks View Post
I dont have the slightest idea, I thought there was no such thing as a computer controlled 700R4 :S
Only the lock up is computer controlled on SOME 700r4s


The computer is there, cause its cheaper.
They assemble all the dashs in one part of the plant and then install them in another part of the plant. If they wanted to leave the computer out they might have to make another branch of the assmebly line, and the cost of tooling could have been more expensive then just installing a ecm whether it needed it or not. So it was easier to make all the dashes for that car the same. Just like how all the shells have the holes for the rear sway bar perches whether it got one or not.
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Old 05-07-2008, 10:17 PM
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