problems with EFI car idle and pressure sensors
Tony Bryant
brd at paradise.net.nz
Thu Sep 20 00:51:44 GMT 2001
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TPS & RPM systems are TOUCHY. The trouble is that at low RPM, the =
slightest hint of a throttle
opening needs to cause a big change in injector pulse length.
Ditch the TPS, and run a MAP sensor instead. Grab a MAP sensor from a =
80's 4AGE toyota corolla,
three wires: 5V, Gnd, and output (0-5V - 4V ~=3D~ 101.3 KPa).
TPS/RPM is not for beginners. Or anyone who cares about idle.
----- Original Message -----=20
From: David Sackett=20
To: diy-efi=20
Sent: Thursday, September 20, 2001 11:30 AM
Subject: problems with EFI car idle and pressure sensors
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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<META content=3D"text/html; charset=3Diso-8859-1" =
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<BODY bgColor=3D#ffffff>
<DIV><FONT face=3DArial size=3D2>TPS & RPM systems are TOUCHY. The =
trouble is=20
that at low RPM, the slightest hint of a throttle</FONT></DIV>
<DIV><FONT face=3DArial size=3D2>opening needs to cause a big change in =
injector=20
pulse length.</FONT></DIV>
<DIV> </DIV>
<DIV><FONT face=3DArial size=3D2>Ditch the TPS, and run a MAP sensor =
instead. Grab a=20
MAP sensor from a 80</FONT><FONT face=3DArial size=3D2>'s 4AGE =
toyota=20
corolla,</FONT></DIV>
<DIV><FONT face=3DArial size=3D2>three wires: 5V, Gnd, and output (0-5V =
- 4V=20
~=3D~ 101.3 KPa).</FONT></DIV>
<DIV> </DIV>
<DIV><FONT face=3DArial size=3D2>TPS/RPM is not for beginners. Or anyone =
who cares=20
about idle.</FONT></DIV>
<BLOCKQUOTE=20
style=3D"BORDER-LEFT: #000000 2px solid; MARGIN-LEFT: 5px; MARGIN-RIGHT: =
0px; PADDING-LEFT: 5px; PADDING-RIGHT: 0px">
<DIV style=3D"FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV=20
style=3D"BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: =
black"><B>From:</B>=20
<A href=3D"mailto:david.sackett at optusnet.com.au"=20
title=3Ddavid.sackett at optusnet.com.au>David Sackett</A> </DIV>
<DIV style=3D"FONT: 10pt arial"><B>To:</B> <A =
href=3D"mailto:diy_efi at diy-efi.org"=20
title=3Ddiy_efi at diy-efi.org>diy-efi</A> </DIV>
<DIV style=3D"FONT: 10pt arial"><B>Sent:</B> Thursday, September 20, =
2001 11:30=20
AM</DIV>
<DIV style=3D"FONT: 10pt arial"><B>Subject:</B> problems with EFI car =
idle and=20
pressure sensors</DIV>
<DIV><BR></DIV>
<DIV><FONT face=3DArial size=3D2>hi, i'm developing a simple =
EFI computer=20
based on a Atmel AVR microcontroller running at 8Mhz for a Uni =
project. I have=20
installed it on my old 1977 Saab 99 and merged it with a Bosch =
D-Jetronics=20
fuel injection system. the car originally had carbies and i have only =
used the=20
inlet manifold, injectors and fuel system from the bosch =
system.</FONT></DIV>
<DIV> </DIV>
<DIV><FONT face=3DArial size=3D2>just to get started I decided to only =
use=20
throttle position and rpm as inputs to the computer. a lookup table is =
used to=20
determine the correct injector open time from these two inputs. we =
have=20
successfully performed test runs in the car and it accellerates fairly =
well.</FONT></DIV>
<DIV> </DIV>
<DIV><FONT face=3DArial size=3D2>the problem we are having is that we =
cannot get=20
the car to idle smoothly. the car refuses to run on all cylinders =
until it is=20
above about 2000rpm. the car runs VERY rich and the plugs have to be =
cleaned=20
every 1/2 hour or so of running. if we reduce the mixture at idle it =
just=20
stalls. also the system fires all injectors at once every revolution =
of the=20
crankshaft. i have replaced much of the ignition system and am fairly =
sure it=20
is working correctly.</FONT></DIV>
<DIV> </DIV>
<DIV><FONT face=3DArial size=3D2>does anyone have any ideas as to how =
to fix the=20
idle?</FONT></DIV>
<DIV> </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=20
to add a similar circuit board mounted sensor. I live in Melbourne =
Australia=20
and cannot find any distributors who will sell me less than 20 with a =
lead=20
time of 12 weeks. does anyone know where i may be able to get just one =
sensor=20
or if there are any other suitable alternatives?</FONT></DIV>
<DIV> </DIV>
<DIV><FONT face=3DArial size=3D2>thanks</FONT></DIV>
<DIV> </DIV>
<DIV><FONT face=3DArial =
size=3D2>David</FONT></DIV></BLOCKQUOTE></BODY></HTML>
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