problems with EFI car idle and pressure sensors

[Bruce]

Don't you mean add a MAP to it?.
Ditching the TPS, would leave you with RPM n MAP.
TPS AE is kind of a must have
Bruce

From: Tony Bryant
Subject: Re: problems with EFI car idle and pressure sensors
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 ~=~ 101.3 KPa).
TPS/RPM is not for beginners. Or anyone who cares about idle.

From: David Sackett
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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