[Diy_efi] New project

[Eck, Joel (Houston)]

stick with speed density, and set it up for open-loop, that way you =
don't have to mess with the O2 sensor. I don't think it would play well =
with the wet exhaust. and I don't think mercruiser uses O2 sensors on =
their efi engines, either.=20

-----Original Message-----
From: Dennis Noordsij [mailto:dennis.noordsij at wiral.com]
Sent: Thursday, November 14, 2002 2:58 PM
To: diy_efi at diy-efi.org
Subject: [Diy_efi] New project


Greetings!

I am new to this list, having browsed the archives many times but now =
doing=20
the formal introduction thing :)

Let's start! The engine is a Mercruiser 470, a 170HP 4 cylinder, 224 cid =
(3.7=20
litres), aluminium block (Merc design) with a Ford 460 head as well as =
some=20
internal parts from Ford, obviously used in in a marine setting. I have =
one=20
myself on a 17' boat, a friend has one on his 20' version.

Let's say my friend is the mechanically inclined one, and I'm more =
useful on=20
the electronics side. He's scrounged up from somewhere a TBI body, 2=20
injectors, built-in pump and regulator, built-in MAP and TPS sensor. I =
have=20
no doubt it'll take him all but an hour to have the whole thing hooked =
up=20
replacing the carb, throttle cable adjusted, fuel return line installed, =
etc.=20

The engines run perfectly fine carbed, so it's completely a for-fun =
project,=20
where a working EFI setup at carb quality would be a complete success. =
The=20
TBI is a bolt-on, so if everything goes wrong the carb can be =
reinstalled on=20
the water if necessary.

His side of the deal ends with a connector with sensor wires and =
injection=20
trigger wires, which is where my part starts.

The sensors on the TBI body are set for a speed-density setup, which =
should be=20
pretty straightforward.

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=20
part starts about say 30-40cm away from the valves) and if they like =
seawater=20
:-) Knock sensors are still not common in marine applications so I am =
sure=20
there are reasons, and probably shouldn't be tried at this point.

An advantage for a marine application is that throttle response is =
nowhere=20
near as important as in a car, as you mostly stick to a certain throttle =
at=20
cruise.=20

I am wondering if there is an advantage in going with a synchronized =
setup, or=20
just go asynchronous based on a small timing loop. Since it's a TBI =
setup it=20
is only replacing the carb so there is no real direct relation with=20
individual cylinders.=20

I have no problem with the theory of speed-density sounding fine and =
dandy,=20
but of course I don't know how it really works in practice, and about =
any=20
hidden gotchas to be aware of. Obviously the volumetric efficiency is a=20
question mark, say it is 90%, but then is it a constant (easily tuned) =
or=20
depending on TPS, RPM, MAP, phase of the moon, etc? How much benefit =
would=20
there be in adding a MAF sensor? (expensive). Marine engines (carbed)=20
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=20
perfectly stoch. mixture?

Ideally, the VE factor would be constant through TPS/RPM ranges and =
tunable=20
with a dial, say between 80 and 100%, and the ECU will persue the set =
mixture=20
(probably also a dial) basing it on ambient pressure, VE setting and =
sensor=20
inputs, with of course special compensation for a cold engine and for =
sudden=20
throttle increases.

I would like the ECU to be based on a PIC, since I have most experience =
with=20
that as well as burners, compilers, etc. Even the 4 MHz part should be =
fast=20
enough to calculate injector pulse times in real-time, A/D inputs are =
more=20
than fast enough, program and data memory should be plenty, and the =
circuit=20
simple enough (only few parts), can be flashed in-circuit. So spare ECU =
boxes=20
can be carried as well, just in case :)

What kind of results would that give?
Anything obvious I am missing so far?

Cheers,
Dennis

_______________________________________________
Diy_efi mailing list
Diy_efi at diy-efi.org
http://www.diy-efi.org/mailman/listinfo/diy_efi

_______________________________________________
Diy_efi mailing list
Diy_efi at diy-efi.org
http://www.diy-efi.org/mailman/listinfo/diy_efi