GerritD

Hi there,
has any one had experience with spark plugs and combustion.
All my spark plugs are very clean except the one from cilinder 6. It is covered in black powder...as if combustion for that cilinder is too rich.

Any idea where to look for ?
- leaking injector ?
- bad compression ?
- bad fuel distributor ?

When accelerating the engine stumbles at the beginning but then accelerates smoothly once 2500 rpm

polecat702

Bad plug wire, check there first, and report back.

GregBBRD

What year is your 928?

GerritD

It is a Euro 928S of 1980. Kjet CIS system

Mrmerlin

Based on your post you have a bad injector
first do the easy stuff check the wire replace the plug then road test if no change then remove the injector and test it for spray and or nleaking

GerritD

thanks MrMerlin, that is what I suspected. I overhauled my engine 2 years ago and recently (6 months ago) checked my compression which were all
good (10 bar). Strangely enough when overhauling my engine I also checked my injectors by a self built injector tester. none of them leaked and spray
pattern was good.
But 2 weeks ago, I decide to clean my injection system by putting An additive into my fuel. Could this have caused one injector to become bad ?

I will first check the injector at cilinder 6 via my injector tester or perhaps just swap it with one of the good injectors and see what happens.

Normally bad compression will not cause blackish spark plugs, it would just make them Brown due to oil loss and even with bad compression
one would have a combustion.

GregBBRD

Common for CIS. Bad injector or fuel distributor.

Swap the injector to a different cylinder and see if the "black" spark plug follows the injector.

This simple test will tell you if the problem is injector or fuel disrubutor.

GerritD

OK Greg, thanks. I will check this. This will indeed provide me a direct indication of my problem.
I'll keep you informed with the result.

GerritD

Here here is a pic of all 8 spark plugs.
Easy to pick out the wrong one 😀



It was indeed a leaking, but very heavily leaking, injector.

allan29

Hello Gerrit .

I see 7 Bosch spark plug and 1 NGK ...
And the NGK goes wrong !

GerritD

Hi Allan, I just used another spark plug instead of Bosch to check whether is was related to the spark plug.

Now that I have your attention , I unscrewed one of the outlet ports on the fuel distributor towards the injector lines, and I noticed a little filter inside the port.
The other ports did not have this filter. Is this normal ? Do I really need the filters ?
Here is an example of such little filters :

GerritD

See the video I made of the leaking injector....it is really bad.

allan29

With this kind of leak , your injector is probably just dirty .
Try to clean it with a bomb of carburator cleaning and air ...
Or of you can , ultra sonic bath ...
This problem came just after you put additive ?
Never use , with CIS injection , additive for cleaning .
All small dirty parts go to the fuel distributor , WUR , injectors who they are mamy many filters and you clogge them with the fine particules .
I don't use the little filters you show because I prefert clean an injector rather than a fuel distributor . More easy !

GerritD

Thanks Allan, actually I wanted to clean
my in and out valves with the additive since
too rich mixture caused carbon on the valves.
any thoughts in cleaning my valves?

I will try to clean the injector the way you
mentioned. Nevertheless will I buy a good
uszd injector of a friend of mine . Just in case
cleaning wont work.

allan29

If you need , I can clean your injectors .
I have ultra sonic and test bench , same like you can see in the manual workshop .