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Fuel Injection

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Fuel Injection

I have never really been a fan of carbs, my Type3 came from the factory with the Bosch D-Jet system and has been very reliable over the last 12 years requiring minimum maintence and only a couple of fixes which is not bad going for a 30 year old car.

I like the fact that FI can be set and left wheras carbs will require retuning over time. A properly setup FI engine will run smoother and have less emission than a comparable carbed engine.

Possible systems that I could use for my project are:

Factory OEM systems:

Bosch D-Jet
Bosch L-Jet
Bosch LH-Jet
Bosch K-Jet
Bosch KE-Jet
Bosch Motronic

Aftermarket/DIY Kits:

Miller FI
CB Performance
MegaSquirt
DTA
SDSEFI

http://www.sdsefi.com/

Each system has it's pros and cons and the characteristics of different systems lend themselves to differnet applications which I'll aim to cover on this page.

The first stage in choosing a system is to decide whether to go with an aftermarket system or adapt a factory system to work. Initially it would seem logical to just go with an aftermarket system as that is what they are designed for. However there are a couple of draw backs that generally affect all the aftermarket systems. Some of the more comprehensive system that are easy to set and tune have had a lot money spent on resarch and development and this is reflected in the sale price. Even if the price is reasonable when coupled to a price of an engine build as in my case it can make it a prohibitive choice. At the other end of the scale is the ultra cheap DIY systems like the MegaSquirt for example. You buy a kit and solder the main unit together and source OEM parts to plumb it all in. A good choice for many but for I am already building an engine and Turbo system from scratch, if I had to make the FI system too I doubt my project would ever see the light of day.

Bosch Systems

Different Bosch systems have been developed over the years. Each system has a different way of measuring the amount of air going into the engine and adjusts the fuel accordingly. Knowing how the systems measure (or meter) the air also helps to identify the different types. Also of note is that all of the Bosch systems can be seperated into two main groups: EFI (Electronic Fuel Injection) and (CIS Contiuous Injection System). Each type of system has different variations.

The left branch in the image above shows the various EFI systems, this type of system, as the name suggests, is controlled electronicaly. The injectors open and close at pulsed intervals, the length of these pulses are governed by an eletronic brain which makes desicions based on information it receives from various sensors. The branch on the right shows the different variations of the CIS systems, this type of system holds the injectors open over a certain pressure and continuosly spray fuel into the manifold.

D-Jet - Druck (Pressure) Manifold Pressure

L-Jet - Luft (Air) - Airflow Sensor

LH-Jet - Luft (Air) Heiss (Hot) - Air Mass

K-Jet - Kontinuerlich (Continuous) - Air Flow

K-Jet description

The amount of fuel that gets sprayed out is dictated by a plunger that has slits in it. As the plunger moves...

...currently updating this page...!

K-Jet System Overview