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'Limit fuel injector pulses'
1999\05\18@195929 by Jon Petty

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Hi everyone

I want to use a PIC or even a stamp to manipulate fuel injector pulses,
mainly reduce the pulse width. I really don't want to utilize individual
injector drivers (for sequential injection systems) that will complicate the
project. As you are probably aware sequential systems usually use an
individual driver for each injector. One side of all the injector has a
common 12v source to all injectors and the individual drivers (sink) control
the ground.

I was wondering if it is possible to modulate the 12v power line which is
common to all injectors. For example say the PIC measures the previous
injector pulse at 5 msec and I want the injector to pulse 2.5 msec on its
next fire. Could I allow the injector to fire normally and cut the power at
2.5 msec (to shut off the injector) and turn power on again in time for the
next injector firing? I am not sure what effect the  rise and fall times of
the power supply will have on injector firing or operation.

If this is possible, I would just need one power control circuit to trim 4-8
injectors. I could easily use a PIC to measure the pulse, allow the initial
injector firing to happen on schedule and trim each injector by controlling
the power source which is common to each injector.

What do you think?

Any comments or suggestions for hardware that could accomplish this?

Thanks in advance

Jon

1999\05\18@210648 by Peter Mcalpine

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Hi Jon,
I think you are going the wrong way about the control of injectors.
A better way to trim injector duty cycle is to modify the inputs
the cars ECU gets, ie vary the signal level from the air flow
meter + or - an amount.. Trick the ECU into delivering less fuel.

Regards
Peter Mcalpine
spam_OUTpetermcaTakeThisOuTspamozemail.com.au - http://www.ozemail.com.au/~petermca
.....mcalpineKILLspamspam@spam@gme.net.au - http://www.gme.net.au
http://www.wrx.org.au


{Original Message removed}

1999\05\19@035112 by Lester Wilson

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Surely less fuel, same volume of air = weak mixture = pinking = holed
pistons?

But form my experience, if you do the opposite to a diesel, you get load
more power and it works with petrol engines but not as dramatically.


Lester Wilson
Crownhill Associates Limited
The Old Bakery
New Barns Road
Ely, Cambs.
CB7 4PW

Tel: +44 (0) 1353 666709
Fax: +44 (0) 1353 666710
-----------------------------------------
http://www.crownhill.co.uk
http://www.towitoko.co.uk
http://www.Edsim2000.com
----------------------------------------

{Original Message removed}

1999\05\19@050015 by Michael Rigby-Jones

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The only problem with this is that tweaking sensor inputs won't give you a
totally predictable change in injector duration, because the ECU calculates
the pulse width from so many variables. Changing just one parameter by a
certain amount won't always give the same change in output.

One potential problem I can see is measuring the pulse width.  Many injector
drivers apply a full 12 volts across the injector to open it quickly and
then pulse the injector drive to keep current consumption/heating to a
minimum.  This would have to be filtered if you were measuring directly from
the injector wiring, obviously not such a problem if you can get to the
injector drivers themselves.

The peak current that an injector draws is very high, you'll have to have
something pretty big to take the current without causing a voltage drop
which would delay the opening of the injectors.  Injectors are quite
inductive as well so you will need to snub the big spikes you get when you
turn them off.

Regards

Mike Rigby-Jones


PS Didn't the SuperChips ICON use a PIC to do something similar?

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> {Original Message removed}

1999\05\19@164509 by Jon Petty

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I didn't tell the whole story, I will be supplementing the missing fuel from
another fuel source. A closed loop air-fuel ratio will be maintained. The on
board vehicle computer will think it is supplying all the fuel.

Thanks

Jon


In a message dated 5/19/99 12:51:46 AM US Mountain Standard Time,
EraseMElesterspam_OUTspamTakeThisOuTcambs.net writes:

<< Surely less fuel, same volume of air = weak mixture = pinking = holed
pistons?

But form my experience, if you do the opposite to a diesel, you get load
more power and it works with petrol engines but not as dramatically.
 >>

1999\05\19@183950 by Dennis Plunkett

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At 16:38 19/05/99 EDT, you wrote:
>I didn't tell the whole story, I will be supplementing the missing fuel from
>another fuel source. A closed loop air-fuel ratio will be maintained. The on
>board vehicle computer will think it is supplying all the fuel.
>

Looks like you will also have to remove the Lambder sensor too. Your task
is not as trival as you think, while from what I have read would work on an
older injection system, the newer load sensing type are a bit tricker, so
your calculations may get stuffed up a bit. Especialy under a fuel dump
cycle (High load cold engine and cold air) Also you may have to watch the
PWM drive to the fuel pump (Perhaps not as there is a mechanical releif
valve).

So does  enthenol like the idea of being subjected to 40 PSI? Or are you
attempting to inject a short cycle of water?

All this aside there is the octane ratting difference and the firing cycle
to look into. I suppose that you are also looking at the sensors that the
engine is using so that you can calculate the extended / change in injector
firing time period.

Try and get an engine with a separte DFI that runs its own fixed / advanced
timing angle when removed / disconnected from the ECU, so that you can at
least break one part of another loop.

Have fun, this should be great.
Dennis


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