300ce engine rough m103

[owensmith]

Hi having probs with engine when idling its very rough but when driving and accelerating everythings fine? Changed leads, plugs, rotar arm, dizzy cap? anything else it could be, also changed the ovp relay. it is a M103 engine 3.0

thanks in advance


Owen

 

[Druk]

Check for an air leak. Vacuum pipe off the manifold somewhere.

 

[owensmith]

Checked that there was one loose coming from the rocker cover and connecting under the fuel distributer are there anymore?

 

[Druk]

You may have to remove the aircleaner to see . There are little pipes everywhere, usually grey coloured, that go to headlight adjust and econometer et al. Not sure if this model has vacuum advance but that's another place to look. The leak (if there is one) could be remote from the manifold so you may have to follow the pipes.

 

[Vlad]

Could also well be the fuel distributor itself, which at this age is prone to getting clogged with years of accumulated gunk.

This tends to show itself up as the car will over fuel at idle, which results in a very lumpy tick over that clears once you rev it, or it might stutter and then clear.

To check for over fuelling, idle the car then switch off and pull a spark plug....if its wet on the end its been overfuelling on that cylinder. Repeat, ie idle, then pull spark plug 2 etc etc etc.

I've had to replace two fuel distributors on my last couple of 300CE's.....using injector cleaner makes the problem worse as it scours the crud off the inside of your fuel lines and it collects in the fuel distributor!!!!

The lumpy idle could also be worn injectors

 

[owensmith]

Thanks for the advice will have a look 2moro and tell you the results can i fit bigger injectors on the car if so where can i get them from or are they universal?

 

[GRAV888]

Thanks for the advice will have a look 2moro and tell you the results can i fit bigger injectors on the car if so where can i get them from or are they universal?

The injectors are specific for your engine type.

 

[Will]

I'm pretty sure with the (old) K-Jet system the 'injectors' are just brass nozzles - the amount of fuel that is 'injected' is goverened by the output from the fuel distributor itself.

Vlad's comments sound quite plausable and wise.

FWIW, it's good to know that Bosch have very recently started to produce many individual spare parts for these older systems that had been unavailable for a pretty long time. I'll see if I can find the link

Will

 

[Will]

Here's the link:

Bosch Automotive Tradition - Parts - Current reproduced products

I would imagine that a local Bosch centre/agent should soon start to be providing access to these parts - great news for us older MB owners who have been at the mercy of secondhand parts or full-priced complete units from MB main dealers for some time.

I'll add this to the favourites section whilst I remember.

Will

 

[owensmith]

Thanx for that very useful

 

[owensmith]

Today checked all nozzels they all seemed fine, also cleaned the butterfly under the the fuel distributer, checked all vacuum hoses all fine none where blocked, still rough idle! atleast its narrowing down!

 

[kth286]

owen

Did the vacuum leak you taped up have any affect on running ?

 

[neilrr]

Did you check the fuse in the OVP?

 

[Vlad]

Re the fuel distributor......how did you measure the flow from the distributor itself.....the reason I ask is that they clog internally which could be the cause of the rough idle.

 

[neilrr]

If bolide were still a member he probably could have told us.

 

[owensmith]

The leak did not have any effect i did not clean the fuel distributer!

 

[Vlad]

Using injection cleaner just accelerates the problem......the fuel distributor will slowly clog up with debris from the fuel lines over its lifetime, leading to erratic fuel distribution, especially at idle which is why this item could well be the suspect.

When you pull away from idle on a light throttle, do you initially get a stutter which then clears the harder you put your foot down?

 

[owensmith]

no there is no hesertation when pulling away or driving its just when its idling!

 

[Dieselman]

I'd go with an air leak into the lower half of the fuel distributor unit. I doubt injector cleaner causes the distributor to clog, more likely it clears gum out of the joints so allows them to leak more air in.

Try spraying carb cleaner round the distributor unit and check all possible air inputs such as the EGR valve.
A vaccum gauge is a good tool for checking manifold vacuum.