problems with EFI car idle and pressure sensors

Wed Sep 19 23:30:15 GMT 2001

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hi, i'm developing a simple EFI computer based on a Atmel AVR =
microcontroller running at 8Mhz for a Uni project. I have installed it =
on my old 1977 Saab 99 and merged it with a Bosch D-Jetronics fuel =
injection system. the car originally had carbies and i have only used =
the inlet manifold, injectors and fuel system from the bosch system.

just to get started I decided to only use throttle position and rpm as =
inputs to the computer. a lookup table is used to determine the correct =
injector open time from these two inputs. we have successfully performed =
test runs in the car and it accellerates fairly well.

the problem we are having is that we cannot get the car to idle =
smoothly. the car refuses to run on all cylinders until it is above =
about 2000rpm. the car runs VERY rich and the plugs have to be cleaned =
every 1/2 hour or so of running. if we reduce the mixture at idle it =
just stalls. also the system fires all injectors at once every =
revolution of the crankshaft. i have replaced much of the ignition =
system and am fairly sure it is working correctly.

does anyone have any ideas as to how to fix the idle?

also i've read about the Megasquirt system that uses an MPX4100 MAP =
sensor, and as a general improvement to my system i wish to add a =
similar circuit board mounted sensor. I live in Melbourne Australia and =
cannot find any distributors who will sell me less than 20 with a lead =
time of 12 weeks. does anyone know where i may be able to get just one =
sensor or if there are any other suitable alternatives?

thanks

David

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<DIV><FONT face=3DArial size=3D2>hi, i'm developing a simple =
EFI&nbsp;computer based=20
on a Atmel AVR microcontroller running at 8Mhz for a Uni project. I have =

installed it on my old 1977 Saab 99 and merged it with a Bosch =
D-Jetronics fuel=20
injection system. the car originally had carbies and i have only used =
the inlet=20
manifold, injectors and fuel system from the bosch system.</FONT></DIV>
<DIV>&nbsp;</DIV>
<DIV><FONT face=3DArial size=3D2>just to get started I decided to only =
use throttle=20
position and rpm as inputs to the computer. a lookup table is used to =
determine=20
the correct injector open time from these two inputs. we have =
successfully=20
performed test runs in the car and it accellerates fairly =
well.</FONT></DIV>
<DIV>&nbsp;</DIV>
<DIV><FONT face=3DArial size=3D2>the problem we are having is that we =
cannot get the=20
car to idle smoothly. the car refuses to run on all cylinders until it =
is above=20
about 2000rpm. the car runs VERY rich and the plugs have to be cleaned =
every 1/2=20
hour or so of running. if we reduce the mixture at idle it just stalls. =
also the=20
system fires all injectors at once every revolution of the crankshaft. i =
have=20
replaced much of the ignition system and am fairly sure it is working=20
correctly.</FONT></DIV>
<DIV>&nbsp;</DIV>
<DIV><FONT face=3DArial size=3D2>does anyone have any ideas as to how to =
fix the=20
idle?</FONT></DIV>
<DIV>&nbsp;</DIV>
<DIV><FONT face=3DArial size=3D2>also i've read about the Megasquirt =
system that=20
uses an MPX4100 MAP sensor, and as a general improvement to my system i =
wish to=20
add a similar circuit board mounted sensor. I live in Melbourne =
Australia and=20
cannot find any distributors who will sell me less than 20 with a lead =
time of=20
12 weeks. does anyone know where i may be able to get just one sensor or =
if=20
there are any other suitable alternatives?</FONT></DIV>
<DIV>&nbsp;</DIV>
<DIV><FONT face=3DArial size=3D2>thanks</FONT></DIV>
<DIV>&nbsp;</DIV>
<DIV><FONT face=3DArial size=3D2>David</FONT></DIV></BODY></HTML>

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