Cleaning Bosch K-Jetronic (CIS) Injectors
I bought a Mercedes Benz 450SLC 5.0 some time ago and I have been slowly in the process of restoring it. The engine has always run lumpy and had a lot of hesitation.
When I bought it, it did not run and required a new fuel pump.
At first, I took it to a Mechanic friend who help me set the CO mixture with a CO meter. This did help the richness problem but it still ran like crap.
The other week, I just pulled the injectors in order to inspect them.
These are not you're typical style injectors (with electronic triggers) but instead, brass nozzles, that spray continuous fuel into the system which is regulated by a fuel distributor.
I managed to get to 7 of the 8 injectors. The one on the back left was impossible to get to without removing the linkage and I did not want to mess with that.
Removal take a bit of time but is quite simple as it's just a matter of unscrewing the hard lines from the fuel distributor, then unscrewing the bold that holds the plate down over the injector.
Be gentle when moving the hard lines so that you do not bend them too much and cause damage.
Upon inspection, I found that every injector was covered in crud and some even had a little rust on them.
Using a wire brush and some brake clean, I cleaned the outside of the injector until it was shiny. This took about 5-10 minutes per injector. Then I used the brake clean with the straw attachment to clean the inside of the injector until I got a decent spray pattern.
Before taking on this job be sure to order the rubber seals that slide onto the injectors as the old ones will probably be as hard as rock.
Putting everything back was simple and exactly the opposite process of removing it.
Once everything was put back together, I left the air cleaner off and started the car so that that I can check for fuel leaks.
The hesitation has gone and the idle has considerably been improved. The car is also a lot more responsive at every speed. It feels like the car has twice the horse power as before.
Here are some pictures:
A dirty and clean injector side by side.
All seven (I couldn't remove the one on the back left because it was impossible to get to) clean injectors.
Injectors with new boots installed.
The cost of these injectors is not expensive (about $30 / injector) however I see no reason why they should be replaced as they are made out of solid brass and will more then likely be dirty.
New rubber seals cost about $1 each and I used about 3 large cans of brake clean for the whole job.
All in all, the whole process took about 3 hours and I would rate the job as very simple.
It will probably take a lot less time on 6 or 4 cylinder cars.
For anyone who has Bosch K-Jetronic injected car (Audi, Mercedes, VW, Ford and Volvo).
I thought I would share this with you as I have found that this exercise is well worth the effort and will greatly improve how you're car runs at very little cost .