OK, I've got everything I need and everything worked the first time except the car would not stay running! I was using the ecm from a 91 bonneville. If I bought a 85 gm something or another ecu for the 3800 v-6, would that ecu work better? Thanks, Greg

I can't make heads or tails on what I would need from mega squirt and one of the forums is on the mid 80's gm setups.

Give us more details man... can't help you much with what you gave us. Does the car start and idle, but then slowly rpm drops until its dead? Does the idle waver up and down? Have you done any mods to the ecu or just used it straight up? I know you said 91 bonneville but what engine? MPFI or TBI? Give us the full workup of the install....

Anything you ever wanted to know about the megasquirt can most likely be answered by its extensive documentation, start here. It is pretty flexible, but by default setup for GM sensors.

Does the '91 ECM require an input from the VATS (vehcile anti-theft system)?

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Joshua

I know my 95 Corvette had the VATS system. I will look in the Corvette book, and see when they first installed it. Maybe all you need is an input of voltage somewhere to get it to stay running. If so, you can use this as a hidden anti theft switch. When the VATS was bleeped on my Corvette, which happened every once in awhile, I would wait five minutes for it to re=set itself, and it would run then. I have no idea why it would act up, but it would start, and then die, which I assume is what you are experiencing here.

Sam

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It's a 225 sl6 in a 67 dart. I built a holley alum. fuel rail with stock GM regulator, MSD fuel pump and ecu and all hardware from a 91 bonneville. The car would start up and run about 5 seconds and die. Like it was getting an initial squirt of fuel and thats all. ( I used a MSD 6a for square wave timing input to the ecu) I purchased a holley projection unit and thought about using it ( it has a O2 sensor) But was thinking about just getting a mid year GM ecu and trying that. I used the setup in this forum for a guide. Thanks, Greg

You need to duplicate the body computer's input to the ECM. You can find little boxes on eBay that put out the correct square wave to fool the ECM. Then it will run for more than 5-6 seconds.

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Joshua

I use the rpm off the MSD 6a for that.

Not the same thing at all. The body module checks the key for the proper resistance value and sends a square wave to the ECM if it's correct. If the signal is absent the engine will run for about 6 seconds and die. Subsequent restarts will run for even less time. It's VATS, vehicle anti-theft system.

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Joshua

If you were to go to an older ECM, other things would change as well. Most of them were batch fired, the 3.8s in, I believe, 85 up were sequential. I am talking about the older version v6, before it became the 3800. The injector size really needs to match the prom in the ecu for things to work at all correctly. The mass airflow sensor is not really a fix all as some believe, but the system is pretty forgiving.

You might have some eprom options available off the shelf for the older ecms that you would not find for the newer ecm.

Bob Dibiasi runs his slant off an 84 or 85 batch fire 3.8 liter Buick ECM. Have you looked this up in the articles section on the Forum here. He gives you years and models to look for.

Sam

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Thanks, that's the forum I tried to follow, only my donor car was the 91 bonneville. What I was wondering, if I could use the same hardware,sensors ect.. and just reconfig. my plug or harness to the older (pre 85 ) ecu? the injectors, maf sensor, throttle position sensor.. all that stuff should work, right? Greg

It will work, but won;t be tuned ideally by any stretch. Eventually you will want to go a tunable ECU.

Sam

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