FI Question

[Dave Bell]

I am curious. I have seen/heard idle hunting on other's cars, and know from rote memory that it is often caused by lean conditions... but what is actually the sequence of events in the FI control and enginge system that would cause the idle to move around and hunt.... Basically I am asking if anyone can fill in the details of the events that transpire.

Dr DDDDDDD... anyone?

Just trying to understand things more

- Dave

[Dave at Pelican Parts]

That's a darned good question. Chux Davis and I discussed that for a little while at one point, and did not really come to any conclusions.

I may be able to ask one or two of the engineers at work. A couple of them are "car guys" and may know the mechanism behind that...

--DD

[Jim Smolka]

The reason for the hunting is a controls problem. Engineers explain things with math, If we could ever find out the "foward transfer function" it is amazing what we could to do the system. Especially, if we could add a feedback loop.


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Smoke Daddy

[Dave Bell]

Jim -

Interesting you should mention the feedback. I have seen that on some systems they actually have a small stepper motor attached to the throttle bypass screw, (or something like that... the details are a little fuzzy). The idea is to read the idle speed and possibly the O2 sensor at Idle and spin the bypass screw a small amount to get the idle set to the right RPM. Helps when you have a heavy electrical load, e.g. high beams, heater blower and tunes going all at once, that is bogging down the engine.

I have toyed with this idea for the 914 but I hardly every have enough juice flowing in my electrical circuits to bog things down... only on cold rainy nights when I have on high beams, wipers and heater blower... guess I need to install some tunes.

- Dave