Controlling Cold Start Injectors With A Pressure Switch

Description

This page describes how to control your cold start injector with a pressure switch.  Cold start injectors can most easily be found at salvage yards on European vehicles that have mechanical fuel injection with the Bosch fuel control system.  These include Saab, Volvo, and Volks Wagon.  There are two sizes that are out there, but there seems to be no easy way to identify them.  They are usually located in the center of the intake manifold; and on mechanically injected vehicles, they are the only injectors with wires coming out of them.  When removing them, cut the fuel line about 2 inches or more from the injector because you will need it.  Also cut off the wire harness with the connector on it, so that you can use it to make the electrical connection.  Remove a couple different ones to try out.

According to Gus, the easiest way to identify them is to apply 12V across the pins and blow through them.  Assuming you found at least one of a different type, you'll find that some are easier to blow through than others.  According to Gus, the injectors that flow better are good for 4psi of additional boost (or 30 HP), while the more restrictive ones are good for about 2psi of additonal boost (or 15 HP).
 

Parts

These are most of the parts you will need to install a pressure switch-controlled cold start fuel injector.  It will vary, depending on how you do your installation.

Installation

Using a pressure switch for this is quite simple.  The easiest place to install the injector is in the air duct near the throttle body.  If you have an intercooler, it has to be installed between the intercooler and the throttle body because the intercooler would cause the fuel to condensate.  About 2 - 6 inches from the throttle body is a good place.  The reason for this is that the turbulence generated by the throttle body ensures that the atomized fuel mixes evenly with the air.  The actual position around the duct that you need to mount the injector will depend on where you have room.  You will have to install it at an angle that will clear the valve cover, hood, etc.

The fuel supply needs to be tapped off of the line to the fuel rail.  This is a 5/16" I.D. hose for our engines.  The vacuum line to the pressure switch needs to come from the manifold somewhere.  Do not use a line that is bled, such as the wastgate or canister purge lines.  Your configuration will then be something like this:

To calibrate this setup, you need to set the pressure switch so that it turns on at the point where your mixture tends to lean out.  If you are using a zener diode or pop-off valve on the MAp sensor, you should set it just above the point where the MAP sensor stops responding.

For further details on this installation, see Gus Mahon's web page, which includes a pictures of the installed injector:

Adding Fuel, by Gus Mahon (skip to the 5th section)
 

Installing Two Or More Injectors

To install more than one injector using a pressure switch, the procedure is the same.  You need all the parts you needed for the first one and should follow the same procdure.  The exception would be the T-fittings because you can tap right into the lines that you made for the first injector and pressure switch.  A two injector setup would be configured like this:

Rather than use multiple pressure switches, you could use an Electronic Engine Performance Controller (EEPC) control up to four injectors.  For more information about install the EEPC, see the Controlling Cold Start Fuel Injectors With The EEPC page.
 
 
 
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This page is maintained by Russell W. Knize and was last updated 04/22/99. Comments? Questions? Email minimopar@myrealbox.com.

Copyright © 1996-2003 Russ W. Knize