FW: Was [Diy_efi] 555 timers

[Daniel Nicoson]

Off line discussion posted.

Dan Nicoson


-----Original Message-----
From: James Seabolt [mailto:turbofiat at hotpop.com]
Sent: Wednesday, January 19, 2005 11:27 PM
To: Daniel Nicoson
Subject: Re: Was [Diy_efi] 555 timers - now off list


Thanks for your email.

At 07:57 PM 1/19/05, you wrote:
>Guys,
>
>It appears the DIY-EFI list is not responding today.  I posted the comments
>below this morning USA Eastern time.  I thought we could keep the
discussion
>going off list until DIY-EFI is back alive.  (Not sure who has that fun
>responsibility of keeping the list alive, but thank you whomever!)


My internet has been down all day!


>I've been thinking about your project of a bare-bones EFI system.  I was
one
>of the ones that suggested a 555 timer based system.

Once I got to thinking about it, it sounded like a worthwhile project.
Although I may have bit off more than I can chew since I haven't put what I
leaned in my digital circuits class to use in years. I did built an air
fuel meter gage about 6 years ago which was my last thing I built
electronic wise. As a matter of fact I got it from the DIY EFI list.


>First, I wouldn't totally rule out your original route of a blow-through
>system.  Check in on the Yahoo groups Jyturbo.  Some of those guys have
some
>blow-through experience and may be able to help you troubleshoot.  In fact
I
>think there is another turbo Yugo there.


I've posted questions concerning this issue on that list and the carburated
blowers list and got no replies. So I'm a bit upset.

Basically what happens is when the turbo starts to make boost, the engine
just cuts out like it's running out of fuel. My air fuel meter gage shows a
lean mixture. When this happens, if I let off then stomp it, I can make 2
lbs but still too lean and the engine runs real rough.

The first thing someone would suspect is I don't have a turbo fuel pressure
regulator and fuel is being forced backwards out of the bowl. But I do. I
even tested it and it does raise the fuel pressure. I even have a TBI pump
that makes 17 PSI of fuel pressure so I know the capacity is there.

The only thing I can think of is perhaps I have too much initial much fuel
pressure. I was told to set the initial fuel pressure at 3 PSI but 5 PSI is
the best I can do. Unless I run a 3/8" return line back to the tank which
was suggested from the place I got the regulator from. Right now I have a
5/16" inlet and a 1/4" outlet. As a test I connected the return line to the
5/16" vent line and was able to get the pressure down from 7 PSI to 5 PSI
but it's still too high.

7 PSI will flood the carburetor and kill the engine.

What I don't understand is how the TBI pump differs from the Bosch pump on
my Spider. On my Spider, the pump will make 60 PSI or more. Yet I only have
a 5/16" return line on that car. But 5/16 appears to be too small for the
TBI pump. Yet is only makes 17 PSI deadhead pressure.

The only thing I can think of is the TBI just has more capacity for flow.

This is probably why I am having problems adjusting my carburetor. I set it
to stoch, make a run up my driveway and when I come back it's either too
rich or too lean.

Perhaps instead of a lean mixture, too much fuel is being dumped into the
engine at boost and is snuffing out the flame. And because of that it just
looks like I have a lean mixture.

Is that possible?

It was suggested I not do this but I'm going to try it anyway. I'm going to
make a restricter to go between the pump and regulator so I can bring the
initial pressure down so I can adjust the pressure with my regulator down
to 3 PSI. Once I do that then maybe I've solved my problem.

What really started my question about this project was I thought about
using a cold start valve to kick in under boost. So the engine just runs
off this cold start valve under boost and doesn't depend on the carburetor
for fuel.

I tested a Bosch cold start valve and it will spray at 17 PSI.

This might work since I'm only running 7 lbs of boost. As long as the
mixture isn't too rich and floods the engine out too early.

>I say don't rule out the blow-through carb setup because the 555 based EFI
>system will take some real time to work out well enough to run a turbo.
Not
>that it can't be done, but it is a whole project of its own. (A VERY cool
>project!)
>
>If you want to pursue the 555 EFI here are some thoughts:

I may have jumped the gun but I purchased a throttle body from a friend of
mine who deals with used Saab parts. I got one from a 16 valve engine. The
one with the throttle positioning sensor. Not the switch like the 8 valve
and the Fiat system.

I tested it and found it has a range of 1000 to 2000 ohms. Sometimes 2500
rpms. But that may just be because it gunked up from blowby. Once it's
cleaned up it may give me more accurate readings.

The interesting thing is this sensor has three wires. If I connect a meter
to say the red and gray wires, the meter shows 1000 ohms at idle and 2500
and WOT. However if I connect the leads to the red and black wire, the
opposite happens. It starts out at 2500 ohms at idle and 1000 ohms at WOT.

If I don't get my own project to work, at least I will have a throttle body
if I go with the Megasquirt system.


>First, how much fuel do you need to deliver?  Will the injector you have
>selected even start to deliver that much fuel?  figure if your engine makes
>90 Hp stock (I know NOTHING about Yugos),

Actually the original 1100 engine made only 55 HP. I've installed a
"larger" 1500cc Fiat motor from an X 1/9. It bolts right in. So that will
give me an additional 25HP over the 1100 engine right off the bat.

I'm estimating at 7 lbs of boost I'll have around 115HP. Doesn't sound like
much but this car just weighs 1800 lbs so that should be enough to launch
it pretty quick.


>7-8 psi typically gives 40-50%
>increase, so you would make roughly 130 Hp on boost.  So if you use
>brake-specific-fuel-consumption (BSFC) of .55(lbs/hphr) then you will use
>.55*130 = 71.5 lbs per hour.  That's a pretty good rate for a single
>injector.  A typical early 1990's Ford V-8 injector was 14#/hr, Mustangs
>used 19#/hr.  These are cheap and plentiful in JY's.  Use several if
needed.

Like I said I thought about using a cold start valve since it's easier to
mount but I do have some Bosch L-jet injectors from my Fiats. I would say
an injector from my Spider would work since that car is making 150 BHP.

But for some reason the dyno said the mixture was starting to lean out at
4500 rpms (not boost related). But I've got some larger injectors from an
L-jet BMW or Mercedes that I have been meaning to install. I believe these
make 170 lbs per hour which is supposed to be right for 150 BHP.

>Pulse Widths etc.  I realize you are trying to set up a throttle body style
>injector (like a carb).  But pulse width limitations will still apply
>regardless of your final injector configuration.

Yes, instead of four direct injectors, I want to mount a single injector
below the throttle body and let the intake manifold distribute the mixture.
I know this isn't as good as direct injection but that's my plan. GM got
away with it back in the 80s.


>For each revolution of the
>crank you must achieve 1/2 of your fueling.  At 6,000 RPM a 4 cycle engine
>has 20ms (micro seconds) to inject fuel at 100% duty cycle, 4,000 RPM
brings
>that max pulse width to 30ms.  Most injectors take from .5 to 2.0 seconds
to
>fully open (this takes away from useable max pulse width).

Interesting. I figured injectors would open and close much faster than that.

So what your saying is, injectors aren't capable of pulsing as fast as I
need them to? I'm a bit confused. Is that why the L-jet system pulses all
four injectors at the same time?

I suppose I'm looking at it all wrong. I'm thinking as simple as a
carburetor is, it couldn't be that much difficult to mimic it's function
electronically. Where a carburetor uses engine vacuum to pull fuel through
the jest out of the bowl. If the fuel being sucked is progressive, looks
like the same thing could be accomplished by progressively increasing the
fuel as RPMs increase. Use the throttle positioning sensor to set the pulse
rate and the injection coil to trigger it.

Sounds too simple.

Another thing. I don't know much about diesels but those early systems as
crude as they were seemed to work OK. I know that the engine has a fuel
distributor like an ignition distributor and it injects fuel at or near
TDC. And I suspect the system has a regulator that increases fuel pressure
depending upon engine vacuum.

Unless the fact that since diesels don't have an ignition system, too much
fuel won't foul the plugs like a gasoline engine so the correct amount of
fuel isn't as critical as it is on a gasoline engine.

Another thought.

As I may have mentioned on my first post, I thought about building a
continuous semi-mechanical injection system.

Where the injector stays open all the time but the amount of fuel is
controlled by a fuel pressure regulator.

I'd really like to know how the old Corvettes and Chevys from the late 50s
to 60s got away with this system. But I haven't found any information on
how this system functioned.

There was a mechanical fuel injection system that Alfa Romeo used. It was
made by Spica. Some say it's a piece of crap. I do know that replacement
fuelpumps are very expensive like $400.
I believe the fuelpump was driven off the crankshaft with a toothed belt.
Maybe it did not use a regulator but instead the fuel was calibrated based
on engine RPM.

Most has been replaced by dual Webbers. I believe it worked like the system
on a diesel engine. But once again I know nothing about it.




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