Troubleshooting K-Jetronic and KE-Jetronic Fuel Injection Systems

Hi, I understand you are having issues with your 1976-1993 C.I.S.-fuel-injected Mercedes engine? You are not alone.

We receive emails almost weekly asking for advice on “what could be wrong” or “what should I do next.” We can give some guidance, but we can’t answer all the questions. Worn-out and faulty systems are almost impossible to troubleshoot via email, and trying to do it is just too time-consuming.

Most problems with the K-Jetronic and KE-jetronic fuel injection systems today are due to the age of their components. From my experience, the lack of regular use and ethanol-based fuels can wreak havoc with the fuel distributor, warm-up regulator (K-jetronic), EHA valve (KE-Jetronic), and the fuel injectors.

One key to narrowing the problem down is performing a fuel flow and fuel pressure test. That is the main reason I developed an accurate, reliable, and leak-free tester. But just doing the test will not fix the problem. It will only show you where it might originate. Even then, fixing the performance issue you are having may be related to factors beyond the fuel injection system.

Here is my advice:

DO THIS FIRST: If you are having engine-related performance issues, don’t assume they are all going to be fuel injection related. If you have weak compression, a stretched timing chain, or excessive engine vacuum. Leaks, you will never get the engine to run right. Do a compression test. Remove the valve cover(s) and check for chain stretch. Test the running engine for vacuum leaks (Google how to do that if you are not familiar with the process. Once you know that none of these are the issue, you can move on to the fuel system.

DO THIS NEXT: If you have not done so already, replace the pumps, filter, and especially the fuel accumulator. A leaking fuel accumulator can cause all kinds of starting and idling problems. Remove the fuel inlet fitting from the fuel distributor and clean the tiny finger screen filter. If this is restricted, it can cause excessive fuel pressure to leak to the ruptured fuel filter and leaking fuel lines. 

FUEL SYSTEM PRESSURE TEST: If you have done this and your readings are “off,” then you will need to do additional troubleshooting and testing. This is where I can not help. I even explain this in my instructions that come with the tester (deluxe kit). I am 80 years old and just do not have the time to answer these types of complex questions.  But I can give you some recommendations.

RECOMMENDATIONS FOR EXTRA HELP.  First, find the original Mercedes technical manual on your engine's fuel injection system and purchase the printed copy. ( usually on eBay) or search online. There are a number of websites that offer this information for download (sometimes at a small fee). Often, the factory manual explains what to do or what to test next if the pressures are not correct.  Secondly, I am going to send you to the website of the person who I feel is the world’s expert on K-Jetronic and KE-Jetronic systems.

He has some troubleshooting articles and instructions available for free. If you should find you have a problem with your fuel distributor or your warm-up regulator (the most common problem on 1976 to 1985 K-jetronic systems), I recommend you contact him and consider having him rebuild your parts or get rebuilt ones from him. I know he is in Australia, but I guarantee it is worth the extra effort to have him help you. https://k-jet.biz

There are also a number of U.S. websites that can provide invaluable troubleshooting information. Do some “deep dive” searching.  Here is an example. https://cisflowtech.com/k-jet-information/

I hope this information helps, and I appreciate your understanding of why it is just not possible for me to answer all the questions I receive. Persevere, and you will eventually solve the performance problems you are dealing with.

All the best, Kent Bergsma