Considering building my own add-on feedback system

[evranch]

So as I've mentioned before my truck runs forever rich due to its large displacement. I started wondering if I can't get the right gas valve, maybe I could adjust the mixture some other way. I looked at the converter port that's supposed to compensate for turbo boost and noticed it changes the mixture rapidly. A tiny puff on it makes it rich and a sip makes it lean out. So what if I could apply a little vacuum to it sometimes? I do automation and controls for a living so why not?

I'm thinking:

- install oxygen sensor, normal or wideband
- install solenoid valve from converter diaphragm port to either manifold or air valve vacuum, probably air valve as not much vacuum is required
- put a measured bleed orifice on the other side of the port (if needed, maybe enough would leak in around the primer button) to return it to atmospheric pressure when not active
- set up a PID loop on a small microcontroller that pulses the solenoid to draw vacuum when the AFR is rich, leaning the mixture out
- some form of throttle position sensing, even just a microswitch to ensure it only comes in at cruise throttle. Maybe just a toggle switch for highway cruise for a start.

In theory that's all that should be needed to lean the mixture in accordance to the oxygen sensor. Wideband could probably be set up to balance exactly or target a true lean mixture, normal would swing rich/lean like a modern car does and stoich is probably the best it could do without getting overcomplicated with more sensors and mapping.

I did some research and found out I basically invented the Impco Commander system, heh. However the Commander appears to basically be defunct/obsolete at this point, and requires a rich gas valve/positive pressure regulator or similar. If I only want to lean out the mixture and not enrich it, anyone see a reason this wouldn't work?

[C3H8]

Yep. You're just reinventing the wheel. You can buy the device you described from Proquip Sales Inc. in Calgary. It's called an EET TEE digital feedback system. It was originally used made for forklifts and then expanded out to the industrial engine market. Many people, including me, used it on pre computer vehicles. I used it on a 1970 Chevy C10. The purpose was the same reason you want it for. It controlled the mixtures from spiking rich too soon. The device is equipped with LED's showing the amount of control. In my case I let the air valve control all the lighter loads, then let the feedback controller control any time the mixtures spike rich too early. The size of the orifice was changed to allow a little richer mixture required at higher loads. I can get the exact part number if you want but they will know what you mean.

[Lpg466]

You can change the spring tension in the converter so that it takes more vacuum to open the fuel and leans the mixture, I did mine today by stretching the spring and bending the lever a bit. I changed my opening vacuum from .5" of water column to 2.75" of water and it leaned the fuel side noticeably. I don't have an 02 installed yet to monitor but will shortly.

[evranch]

Not sure I want to mess with the spring tension in the converter, I like to be able to reliably set them back to their factory setting. Just adjusted the one on my tractor last week as it was running rich, turned out the arm had somehow got up too high. Back to stock and back to running great.

Will take a look at the EET TEE system you describe, though if the concept is valid I might try this experiment just for fun as I do think I have enough parts laying around to give it a try. For some reason I find this sort of thing to be fun