$35 Additional Injector Drive Mk II


This note contains many modifications which may void your vehicle's warranty, or even be illegal in some areas. It is your responsibility to check the validity, safety and legality of anything here.
If you want an all-singing, all-dancing controller this is not for you. If you want an effective, low cost solution to getting a little extra fuel into the engine when it needs it, then read on.


Additional injectors under the control of the factory computer are one solution to dealing with increased boost, and possibly a fuel-cut defender. The problem is, how do you drive the additional injectors?

The simplest answer would be to wire an extra injector in parallel with the original. This will work if your computer has the current ability to handle it, but many don't and a blown computer is very expensive. A better way is to use the drive signal to control, but not drive the additional injector. Sounds simple huh? Actually it is...

The advantage of this method is that if we add just one injector, the ECU, via the readings from the Exhaust Oxygen Sensor (Sometimes called a Lambda, or EGO Sensor) will normally be able to keep the mixtures in check.

The original version (click here to find it) used a simple darlington switch to do the job.  This version (called Mk II) enhances that design to provide the following features:

Unfortunately, the price has gone up a little, because we now have a specialised integrated circuit which manages the injector.

The Circuit

This is a revised and expanded version of the original DIY_AID published on this site. All the enhanced features are provided by a LM1949 Integrated Circuit, which is manufactured by National Semiconductor
Label Item
Q1 2N6044
U1 LM1949N
U2 7805P
R1 0.1 Ohm, 2W
C1 0.01uF
D1 33V, 5W Zener

The schematic for the driver is available in two forms:
Download the Protel Schematic file by clicking here
Or as an Adobe PDF file here


Picking an Injector

Installation and testing

Going Further

So what if you need even more fuel? You can run multiple copies of the circuit, connected to other injectors.

Back to the FAQ