[Diy_efi] New project

[steve ravet]

Dennis Noordsij wrote:
> 
> Greetings!
> 
> I am new to this list, having browsed the archives many times but now doing
> the formal introduction thing :)
> 
> Let's start! The engine is a Mercruiser 470, a 170HP 4 cylinder, 224 cid (3.7
> litres), aluminium block (Merc design) with a Ford 460 head as well as some
> internal parts from Ford, obviously used in in a marine setting. I have one
> myself on a 17' boat, a friend has one on his 20' version.

Hi Dennis, I've got that same motor in a 17' runabout.  I bought an ECM
(GM 1227748) a long time ago and collected some info about it with the
intention of putting it on the boat, but never got around to doing
anything.  I was going to use a 4.3L V6 throttle body with it.  When I
pick up that project again, I'll probably use megasquirt instead. 
Megasquirt is fuel only, but by the time I get around to doing anything
Bruce may have upgraded it to fuel and spark.

If you're set on rolling your own around a PIC, browse around the gmecm
page and archives and you can get an idea of what algorithms GM uses,
and think about which parts are applicable to you.

> Because of the wet exhaust I am not sure if we can use any kind of lamda
> sensor, don't really know how far they should be from the exhaust valves (wet
> part starts about say 30-40cm away from the valves) and if they like seawater
> :-) Knock sensors are still not common in marine applications so I am sure
> there are reasons, and probably shouldn't be tried at this point.

IMO knock sensors are uncommon for the same reason that point triggered
ignitions are common.

> I have no problem with the theory of speed-density sounding fine and dandy,
> but of course I don't know how it really works in practice, and about any
> hidden gotchas to be aware of. Obviously the volumetric efficiency is a
> question mark, say it is 90%, but then is it a constant (easily tuned) or
> depending on TPS, RPM, MAP, phase of the moon, etc? How much benefit would
> there be in adding a MAF sensor? (expensive). Marine engines (carbed)
> traditionally like to run a bit rich, typically 12:1, and because of the
> constant load and lack of cat. convertor is it necessary to persue a
> perfectly stoch. mixture?

The most fundamental table in a GM SD setup is the VE table, indexed by
RPM and MAP.  Then there are adders for sudden changes in TPS, for
coolant temp, for throttle near WOT, etc.

Keep us posted, I'd like to hear how it turns out.

--steve


-- 
Steve Ravet
steve.ravet at arm.com
ARM,Inc.
www.arm.com

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