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-   -   What does that knob do mister ? (http://www.aquamist.co.uk/forum2/vbulletin/showthread.php?t=3158)

jondee86 15-12-2018 09:50 AM

What does that knob do mister ?
I have just fitted some larger fuel injectors which means using the GAIN
control on the HFS3 to increase the W/M injection rate. I calculate that
I need a gain of around 38% and access the controller to make the
adjustment. Bearing in mind that I have to make a WOT pull to redline to
log the HSV duty, I figure it would be a good idea to get the gain setting
in the right ballpark before taking to the road.

This is when some questions arise for which searching has been no help...
1. Does the control turn ACW or CW to increase the gain ?
2. If there are five settings either side of "12 o'clock", is it correct to say
that one step in the positive direction is +40%, and one step in the other
direction is -5% ?
3. Do the trimmers actually have a fixed number of finite steps or are they
in fact fully variable between their stated limits ?

Someone has to ask the "dumb" questions :)

Cheers... jondee86

Richard L 15-12-2018 11:14 AM

Re: What does that knob do mister ?
A couple of question first for more accurate answers:

1. Which version of HFS3 do you have?
2. What is the maximum duty cycle are you running at present (larger injector)?

jondee86 15-12-2018 10:30 PM

Re: What does that knob do mister ?
I have version HFS3-3.1

With 440cc/min injectors the max DC would typically be 90% and sometimes
a little higher. I have changed to 550cc/min injectors and reset the HFS3
jumper to the 1.25 scalar position.

As a side note, I had assumed that the larger injectors being 25% larger
would result in a 20% reduction in IDC. However, looking at the logs I have
made to date, it appears that the performance characteristics of the two
injectors are not the same, and simple proportion does not apply. So my
guesstimate of requiring 40% gain is now out the window !!

Cheers... jondee86

Richard L 16-12-2018 07:30 AM

Re: What does that knob do mister ?
you are in full control due to good knowledge of the system. Most impressed.

The iDC prescaler is perfectly set. Gain is completely up to you, at 12pm is 1:1, so the FAV will not peak early. You can confirm this with the "95%"red led onboard at full load. Don't forget to watch the road.

jondee86 20-12-2018 01:02 AM

Re: What does that knob do mister ?
Yes... I was over-thinking the issue and forgot that the W/M injection
signal in my log is the flow meter rate and not an IDC or FAV pulse rate.
The change in fuel injector size is primarily to get the maximum IDC down
to under 85%, and does not mean I will be delivering any more fuel to the
engine. So all I have to do is check that I am getting the same W/M log
rate as before.

As you say, it looks like the x 1.25 jumper will do that without any need
to fiddle with gain control.

Cheers... jondee86

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