cis 3 pot to map sensor conversion questions

[Alan Pritchard]

Looks like I did well then. Randomly bought a 1 bar map of a corvette
lt1???? (excuse my ignorance, we don't get many big American sports cars
here in the uk), figuring it would be normally aspirated. If it were not the
right range, one of our elec tecs would be able to knock up a
reducing/multiplying circuit for me easily enough.
Well the ms kit is just about ordered, first goal is fuel only , then go for
squirtnspark. In the meantime its just a case of getting everything done
that I can, and collecting parts!!!
 -----Original Message-----
From: 	Jim Green [mailto:jeg1976 at yahoo.com] 
Sent:	25 November 2003 15:04
To:	Alan Pritchard; Quattro List (E-mail)
Subject:	Re: cis 3 pot to map sensor conversion questions


--- Alan Pritchard <apritchard at seaeye.com> wrote:
> This has been talked about on the Megasquirt list,
> and Javad has also put
> some info in his 034efi documentation. I would like
> to stop using the pot on
> my 90q (mainly so its easier to go efi) and plan on
> using a map sensor (GM
> recommended). Firstly, what is the output of these?
> According to a website,
> put 5v into a 2 bar sensor, get 2.5 at atmospheric
> 0v at vacuum and 5v at 2
> bar (If I recall correctly or the other way round). 
> 034efi recommends a 1bar sensor, which, for my app
> seems to make sense
> (currently NA) so I guess the ecu would see 5v at
> idle (or there abouts)
> Next question, the cis pot gives out 0-5v  across
> its swing. Is that 0v with
> the plate at rest, and 5v fully open?? If so is that

Correct

> not inverse to what the
> map reads??

Nope MAP sensors read 0v near 0 bar atm.  and 5v at
whatever the top range is, 2.5 bar atm. in the MS I
think.

> So in theory it would be possible to advance my
> timing across the range by
> raising/reducing the voltage that the ecu sees from
> that device??? So I
> could rig up a sort of "sport mode" button inside
> the car to use more
> advance (where fuel allows)
> Thanks for listening to my ramblings!!!!


Alan, the goal is to fake the CIS3 computer into
thinking nothing on the engine is out of wack.  I wish
it were as simple as just feeding it a load signal and
having it pull timing, but it knows when the load
doesn't match engine RPM's and what ever else it might
be monitoring.  Then it goes into a limp mode, not
full retard, but retarded enough to really piss you
off.  The 1 bar seemed to work best for me, but idealy
I think that a 1.5 bar sensor would work perfect.  Not
sure where you can find one.  The 2.5 bar sensor
woun't give the ECU full voltage often enough to keep
it happy.  

The CIS3 will work, but you will not be happy with it.
 Afer you get the fuel running, I'd quickly look into
the MS'n Spark, or megaspark or whatever's out now. 
Just a simple mappable ignition will be way better
than the CIS3, as long as it has air temp timing maps.
 That's a biggie in the turbo world.


HTH,


=====
Jim Green
'89 80q slow
'89 90tq fast, really fast
http://www.mswanson.com/~jgreen/car_home.html

__________________________________
Do you Yahoo!?
Free Pop-Up Blocker - Get it now
http://companion.yahoo.com/