<VV> Production ECMs Re: EFI Info Re: OBD-II for Corvair

Mark Durham 62vair at gmail.com
Wed Oct 13 18:50:43 EDT 2010


LONG - Frank, the OBD I ECM's have a programmable Eprom, a chip you can pull
out, and program using software and a computer. Read Ted Brown's site,
www.corvairnut.com he talks quite a bit about that. The fuel maps and
ignition maps are programmable on all of the Eprom.

The OBD I computers have a learning circuit based on O2 levels, so using a
heated O2 allows the computer to adjust to your unique engine to a certain
extent. But you have to get it right to begin with. You have to know the
cubic inches and horsepower of the engines, and how many pounds per hour of
fuel required which can be determined off of that, and it all is fed into
the Eprom chip for the computer to use.

Craig Nicol took a Pontiac Fiero 2.8L V-6 system off and put it on his 2.7L
140HP Corvair and did NO mapping changes at all, and the car gets close to
30 mpg on the highway and runs at least as strong as it did on 4 carbs. So,
if you find a system matched right, there is little to do.

My EM has the 102hp  145 CU 2.4L engine, smaller than the 2.8 Fiero or his
Corvair 2.7, which are pretty evenly matched for horsepower, I think the
Fiero's 2.8 is 145 to Craigs 2.7 at 140; but my 145 CU engine with bored out
throttle bodies will only produce about 124. Do I need to compensate?  Lets
see.

The Fiero and Craigs motors use 6 injectors and produce 140-145 HP out of
2.7/2.8L
That is .853658 HP per cubic inch of displacement.
My 145 CU 2.4L 124 HP engine will produce .855172 HP per cubic inch.
I'm using 4 injectors for that, two per side.

So, the larger engines produce .853658 HP per CU to my engines .855172.
Almost a match.

I'm thinking that what the computer see's for my engine and what it would
see for Craigs engine would be almost identical. So, I think the fuel and
ignition mapping would logically be similar. My performance will be slightly
less because my car is of a similar weight to Craigs, but I think the
similar mapping will work.

Even so, There is a guy on the Fiero Forum that has done dozens of upgrades
to Fiero's using my type 1223370 computer in the 2.8 motors, who thinks he
already has a mapping he can use to start with.

We'll start from there, get it running, and see where it leads us.

regards  Mark Durham



On Wed, Oct 13, 2010 at 2:25 PM, <FrankCB at aol.com> wrote:

>  Mark,
>
> For you guys using ECMs from production vehicles, how do you go about
> CHANGING A/F ratios and ignition timing from the stock NON-Corvair settings
> to fit what's needed in your Corvair, especially if you've made
> modifications to the stock Corvair?  On the MegaSquirt units you can take
> advantage of the feedback from wide-band O2 sensors for the A/F and can use
> Ray Sedman's SafeGuard with optional display to help you set the timing.
> Unless, of course, you simply put the Corvair on the dyno and use the
> results to change the MegaSquirt settings you start with.  But how do
> you change factory settings of production ECM units that are designed to
> work with NARROW-band O2 sensors that try to run the engine at
> stoichiometric A/F and timing that is set for combustion chambers much
> different from Corvairs??
>
> Frank "old dog trying to learn new tricks" Burkhard
>
>
>  In a message dated 10/11/2010 2:16:14 P.M. Eastern Daylight Time,
> 62vair at gmail.com writes:
>
> Thanks Frank, its actually Charlie who is the receiver here. I've already
> am
> about half way through my EFI project. And, I've already been on the DIY
> EFI
> site quite a bit. Rather than building my own board, I bought a rebuilt
> 1223370 GM 90-92 Camaro stick ECM and chip for $50. I just finished my
> wiring harnesses for the ecm (3 of them) and have acquired most of the
> parts. I'm modifying the carbs to straight throttle bodies boring out the
> venturi and ecpanding the bore to 1.33", will make a new set of throttle
> plates for it. Have all the sensors, etc. Just waiting for bad weather to
> bring the car inside (I still want to drive it on sunny days) and the
> conversion will begin!
> Mark Durham
>
> On Mon, Oct 11, 2010 at 10:16 AM, <FrankCB at aol.com> wrote:
>
> >  Mark,
> >
> > A good idea to get started with this is to go to   www.diyautotune.com
> > and click on the "Tech Articles" button to access a number of detailed
> (with
> > pics) articles.  The first is a conversion of a carbureted Chevy V-8 to
> > throttle body EFI.  Others cover multiport EFI. Whether you use the
> > MegaSquirt or go to an EFI from a production car, these articles will
> give
> > you a lot of insight into what's needed and how to go about it,
> > step-by-step.
> >
> > Incidentally, you can build your MegaSquirt from a kit of parts OR buy
> one
> > already assembled.  If you build it yourself, I recommend getting a
> > Illuminated magnifying glass light as well as a temp. controlled
> soldering
> > iron with a VERY small tip.  If you don't have experience soldering micro
> > circuit boards, I suggest buying the already assembled unit.
> >
> > Frank Burkhard
>
>


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