Why a computer?

[GreyGoose006]

Hey I was just wondering what a computer can possibly do in a carbureted car. i have a '84 3.8L w/ a computer that is telling me that the car is running rich, but the car is pinging. i may be missing something, but this shouldnt be possible, should it?

[PeteA216]

The engine running rich is probably the cause of your pinging. Thats how it was in my '84 Caprice (5.0) when I first got it. All the computer really does is try to keep the car running as efficiently, and environment freindly as possible. If its running rich, you can try to adjust the mixture, but I wouldn't recommend it if you're not all that experienced with carburetors.

[96capricemgr]

People like to think only lean can cause pinging but overly rich certainly can as well. The computer basically makes small changes to the carbs operation at cruise to monitor and ensure proper AFR.

[PeteA216]

Now that I think about it, the only major thing that the computer does contol is the advance and retarding of the distributor. Its replaced the vacuum advance on the HEI distributor.

[Blue Bowtie]

Originally Posted by PeteA216

Now that I think about it, the only major thing that the computer does contol is the advance and retarding of the distributor. Its replaced the vacuum advance on the HEI distributor.

If you think about it a little more, you'll remember that the ECM also controls the mixture control solenoid on the carburetor, the PWM of the EGR solenoid, the TCC lockup points, knock retard and recovery, as well as the timing.

If the EGR is not funtioning, you'll get lots of "ping" and detonation.

[PeteA216]

Ahh true, looks like the computer is a little more important that I had realized. If the car were to be converted to a non computer setup, I know you'd have to change the carb and the distributor, but how would you contol the TCC?

[Blue Bowtie]

It can be done using a pressure switch in place of the transmission 4th gear switch, a throttle switch, and the brake pdeal switch. It's a very crude system, and retaining the ECM is just easier.