Building an Electronic Fuel
I work as an
automotive technician at
my "day job". Nearly all of the cars I work on have fuel
injection systems. They all have several things in common: a control
unit, a fuel pump, sensors and fuel injectors. Fuel injectors are
made up of a coil of wire which opens a valve when energized. It's a
basically an electronic solenoid valve.
As time goes by these
"valves" can wear out and become sluggish, leaky or just
quit working. They're pretty easy to test by simply applying 12 volts
to the leads and listening for a click sound. But, that doesn't tell
the whole story. A better way to test them is to send a series of
electrical pulses to them and see how much fuel they deliver. First a
fuel pressure gauge is connected in line on the fuel rail, then the
fuel pump is turned on momentarily to build pressure then turned off.
The fuel injector gets a pulsed signal for a given duration and the
pressure drop is noted. The process is repeated with the remaining
injectors for comparison. Sometimes a few may have a different
delivery rate which can be a great aid in troubleshooting a poor
These devices are available for $140 - $400
depending on their capabilities.
I decided that I could build one
myself for very little money using the classic 555 timer chip and a
few external components.
Below you'll find a list of parts and some links to a few web pages
that will help you understand the workings of the 555.
also a build video which will show you how I put this together.
This circuit will output a series of square wave pulses that
are 8 mS on and 7 mS off for a duration of one second.
A word of
caution about the N-channel MOSFET.
Be very careful of the pin outs! These tend to vary depending on the
manufacturer. Make sure you know the exact location of the gate, drain
and source! Connecting one wrong will fry the 555 chip AND the
Be sure to add a protection diode between the source and drain even
though most MOSFETs have them internally.
Notes on the
been revising the schematic as I receive suggestions from people. Here
and there I've added a few resistors and diodes that were not on the
original design. Feel free to send any suggestions my way and I'll
include them. If you can't find LEDs that are rated at 12 volts, be
sure to add the proper resistor in series with your LED.
I've had a few emails asking if this will drive a Diesel injector. The answer is, NO.
The MOSFET in this circuit is rated at 4 amps and Diesel injectors need
15 - 25 amps. Attempting to drive this kind of load will damage the MOSFET and possibly other components.
However, you CAN replace part # IRF510 MOSFET with a part # MTP75N03HDL Motorla MOSFET. The Motorola has a 75 amp rating.
Here is the datasheet: http://www.datasheetcatalog.org/datasheet/motorola/MTP75N03HDL.pdf
Here is where to buy one: http://www.allelectronics.com/index.php?page=search&search_query=MTP75N03HDL&x=0&y=0
UPDATE ON NEW
I've designed another schematic below with two
more switches and a 4.7 mF capacitor added.
SW1 is used to choose between a timed or continuous ouput.
SW2 is used to choose between a 1 second or 5 second ouput.
The only extra parts needed to build the circuit this way are:
1 - 4.7 mF capacitor and 2 - spdt switches.
I've updated the parts list to include these extra parts.
I encourage you to try building other circuits with the 555. It's a
very versatile chip with many applications.
Have fun and keep on making stuff!
Questions? Email me at: email@example.com
Dean Segovis - All Rights