K-Jet Frequently Asked Questions

1 What is K-Jet anyway? What does it mean?
2 Why do so many people say, “I hate K-Jet!”
3 Why do you bother to even write this page? Everyone knows X is better.
4 Are there different versions of K-Jet?
5 How do I know what kind of K-Jet system I have?
6 What is CIS (Constant Idle Speed)? Is it the same as CI?
7 My K-Jet car is not running right – where do I start looking?
8 My K-Jet car is still not running right – now what do I do?
9 Can you describe the K-Jet system in detail?
10 How about a video demonstration?

1 – What is K-Jet anyway? What does it mean?

K-Jet or K-Jetronic is a mechanical fuel injection management system developed by Bosch. The K-Jet system can be found on a lot of Volvo automobiles as well as on other makes. It is called K-Jetronic because it was developed by the German company Bosch, and they called it “Kontinous” to describe it’s Continuous Injection (CI) nature. That is to say, the injectors are always squirting fuel, they are not pulsed like many electronic fuel injection systems. For more info please read the introduction to this site on the “About page.

2 – Why do so many people say, “I hate K-Jet!”

People often say this because they can’t figure out how to solve a problem with their K-Jet car and are angry. K-Jet really isn’t any worse than any other fuel injection system if it’s working properly, it’s just that K-Jet’s successor, LH-Jet (an EFI system) was less troublesome to fix and is found on more Volvo’s, making parts more available. K-Jet is also harder to performance tune than LH-Jet.

3 – Why do you bother to even write this page? Everyone knows X is better.

Yes, there are aftermarket engine management options (MegaSquirt and Spark, Haltech and others) and there’s always the option of converting to LH-Jet. However, aftermarket engine management is really only necessary if you’re running a high horsepower turbo car. Converting a K-Jet car to LH-Jet is not very easy and requires a “donor” motor or car that you can get the LH-Jet system from.

So yeah, you can spend $500 to $1000 on aftermarket engine management (plus a ton of labor) or maybe $500 in parts to convert to LH-Jet (plus a ton of labor). Yes, it can be done and has been done, but it really isn’t the most feasible option for most people, considering that any Volvo old enough to have K-Jet probably isn’t worth more than $500 to $1000 anyway. Really though, K-Jet isn’t that bad. It is ridiculously reliable compared to many alternatives of that era, and it couldn’t have been that bad – Volvo used the K-Jet system in the Group-A 240 race cars.

4 – Are there different versions of K-Jet?

Well, yes and no. LH-Jet, for example, has many specific versions, such as 1.0, 2.0, 2.2, 2.4, 3.1 etc. K-Jet basically has two versions, Turbo and Normally Aspirated (N/A). The main difference between these two are the location of the different parts, not the workings of the system or the types of parts.

However, as K-Jet evolved, changes were made and other systems were tacked on. The PCV (positive crankcase ventilation) system was altered, the control pressure regulators were changed, the Constant Idle Speed (CIS) system was added, the Lambda-Sond emissions-control system was added (if required by law) and other small things changed. K-Jet systems varied (sometimes extensively) in their layouts, but not really in their components between different countries and between different motors. Again, this website focuses primarily on USA models.

5 – How do I know what kind of K-Jet system I have?

As far as I have been able to figure out, it goes like this:

Year (240 Series, USA only) System CIS Lambda-Sond Engine
1981-1985 TURBO K-Jet Turbo Yes Yes B21FT
1982.5 N/A LH-Jet 1.0 (not K-jet) Yes Yes B21F
1982.0 N/A K-Jet Yes Yes B21F
1981 California Car K-Jet Yes Yes B21F
1981 Federal Car K-Jet No Yes B21F
1977-1980 K-Jet No Yes B21F
1976 K-Jet No No B21F
1975 K-Jet No No B20F

6 – What is CIS (Constant Idle Speed)? Is it the same as CI?

CIS is an electronic system to keep your idle speed constant using an onboard computer and an Idle Air Motor. The idle air motor allows air into your engine like a valve. The openness of the idle air motor is controlled by the CIS computer. The differences between a CIS and non-CIS car are detailed on this page.

CI stands for Continuous Injection. All K-Jet cars had CI by definition of the K-Jet system (Kontinuierlich Jetronic) system. CIS was an addition to the CI system. Many people think there is some confusion between these two terms. CI-System is sometimes abbreviated as CIS (Continuous Injection System) and is thus confused with the Constant Idle Speed system. However, as far as I can tell, this mistake is not made in the Volvo Greenbooks, only in other manuals and websites. The Volvo shop manuals refer to the two systems as the CI-System and the CIS-System.

7 – My K-Jet car is not running right – where do I start looking?

What you do depends on what sort of symptoms your car is having. If your car is a 1980 to 1987 car, don’t even bother with anything until you’ve replaced your engine wiring harness. A lot of problems are caused by shorts in the engine wiring caused by a premature degradation of the wire coating.

You can buy one $200 to $400 USD or you can build your own for about $30 to $50 in materials plus about 2 days of your time. For more info on building your own wiring harness, check out this page.

8 – My K-Jet car is still not running right – now what do I do?

Check out this article on Debugging K-Jet systems for some help. Otherwise, go to some of the online forums in the Links section of this site and search for your problem. Read, read, read before you post a new question, it’s almost certain that your problem has occured before and has been solved. Remember, “It’s great to learn, cause knowledge is power!”

Of course, K-Jet is not always to blame for problems with your car. It could be caused by some other problem (bad distributor or spark plug wires, etc etc.) that has nothing to do with the fuel injection system.

9 – Can you describe the K-Jet system in detail?

Of course. You can read all about the wonders of the glorious, ever-victorious K-Jetronic fuel injection system on this page. It is a constant work in progress as I learn more and more, so don’t expect a doctoral thesis or anything, although it is getting quite long.

10 – How about a video demonstration?

Some cool people in Europe somewhere made this amazing video of K-Jet in action, outside of the car. I found it floating around on the internet, and decided to host it here.

Download! (mpeg format, 2.82MB)