BoatBanter.com - View Single Post - I still don't want the stuff in my boat tanks

JustWait

On 1/3/2012 3:29 PM, wrote:
On Tue, 03 Jan 2012 10:29:26 -0500, JustWait
wrote:

On 1/2/2012 11:44 PM, wrote:
On Mon, 02 Jan 2012 21:46:40 -0500, JustWait
wrote:

There is a moment in time when you first go to start your engine called
"key on, engine off" when the computer gets it's charge and looks at all
the sensors for their 0 (zero or null) reading. The IAC (idle air
control) for example is a small piston in the side of the intake which
bypasses the throttle body and makes micro adjustments to the air flow
to the intake while the gas pedal is off, and the throttle body is
closed. This is necessary with injected cars to allow for changes in
load from other equipment on the car, etc... The IAC has a capacity for
movement and that distance (the throw of the piston) is segmented into
256 units. When the vehicle enters that KOEO moment, the IAC closes all
the way and the computer notes where it bottomed out in along it's range
of motion of that 256. Let's say the piston bottoms out at positition 7,
the computer uses that setting as "zero" in it's calculations for the
remainder of the engine run... If there is **** and carbon in the IAC
for instance and it can't really zero out, the car will idle ****ty...

The idle control solenoid on a Mercury EFI 60 is just on or off. It
crosses to a Cummins diesel part if you look hard enough. It just
pulses the solenoid at idle.

Are you sure there it's just open and closed, and no adjustment in
between?? That doesn't make sense, is there only two loads given to the
engine at idle? Is the ambient air pressure always the same? Air and
internal water temps, etc... Just doesn't make sense. Why have a piston
and seat if that's the case???

Yes, I am sure there is only two states, open and closed and the shot
that picks it is 12vdc (looked at on a scope)

So, you are saying you saw a 0-12 volt square wave on/off on the scope,
coming off the computer?

They just use pulse width modulation to control the air flow
The first time I had a bad one I spent quite a while in the driveway
proving to myself that I would actually fix something when I replaced
it. I could actually get a decent idle pinching the (disconnected)
hose down with miniature vice grips adjusting the gap with the bolt in
the handle. It just did not have the "dash pot" function.

Again that just doesn't suggest an off/on, it more suggests that the
opening is variable beyond on and off... I know the computers back in
the 80's went from ten dumps a second to hundreds, if that solenoid was
slamming open and shut hundreds of times a second, I can see where there
would be lot's of problems...
I took the valve apart and when I couldn't really find anything wrong
I decided it must just be binding and I put some light machine oil on
the piston and it worked a little better.so I ran it a week or so like
that, waiting for the part.

Like I said, the next time it started getting cranky, I just ordered
the solenoid and threw it in.