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  #1  
Old 06-13-2005, 06:24 AM
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300E running rich on two cylinders - Solved!

Oh woe! The fuel system is acting up again.

I have been experiencing some kangarooing with my 300E, driving at low speeds with a steady throttle. I thought this was due to backlash in the drivetrain but have been advised in this forum that it may well be a weak mixture - thanks Duke2.6 - so I tweaked the mixture and have managed to get the problem under control, not eradicated entirely but at least its now barely noticeable.

Unfortunately, during my investigations, I've discovered that the engine is running rich on cylinders 1 and 6 but seems to be Ok on the other 4 pots. The offending plugs are a sooty black, dry not wet.

I've just put in new plugs, changed the fuel filter and bled the crap out of the fuel lines. The distrib cap and rotor were replaced about a year ago, as were the coil, plug wires, injectors and seals. I've swapped out the FPR with a known good one, all to no effect.

The engine doesn't seem to burn oil between changes at 5,000km and runs fine on open throttle, its just at a steady throttle it starts bucking. As I said, richening up the mixture helps but at starting idle, the engine runs a bit lumpy, just like its not firing cleanly on all cylinders. My mechanic set the mixture by feel, adjusting it until the engine ran smoothly at idle. Hopelessly unscientific, I know, but I don't have the luxury of a lambda system and the attendant electronic feedback. I had to stop and tweak the mixture 1/2 turn richer today after i took the car out for a run.

I'm now reasonably certain that the kangarooing is a mixture issue but not sure why it would be running rich on two cylinders and fine on the others.

So, I'm seeking pointers as to where to start looking next.

Fuel Distributor?

Valve stem seals?

Potentiometer (I have a new one)?

ECU?

Any suggestions most welcome. I've just reviewed the result of my search and a 2001 post from stevebfl (praise be!) suggests the valve stem seals may be the most likely culprit. Anyone care to back this up?

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Last edited by simmo300e; 06-26-2005 at 04:45 AM.
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  #2  
Old 06-13-2005, 11:35 AM
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As built the maximum injector valve flow dispersion should be within two percent. Over time flow rate dispersion can digress due to deposit buildup or chatter valve wear.

The first thing to try is a bottle of reputable injector cleaner in the fuel.

If this doesn't help the injectors can be removed for cleaning, flow and leak testing if a shop in your area has the equipment.

The last solution is to buy and install a new set of injectors.

For those with lambda systems that require periodic emission testing, the above is probably why many M103 engines have high HC readings which tend to get worse as miles accumulate.

Duke
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  #3  
Old 06-13-2005, 08:23 PM
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The injectors were replaced a year ago by the dealer, is it likely they would start to gum up in that time? I did try some additive last week, prupose being to remove water from the fuel, if anything the problem got worse.
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Old 06-13-2005, 08:58 PM
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No, injectors should not clog or degrade in a year, but I don't know the quality of your fuel. All US gasolines have deposit control additives.

"Fuel driers" are primarily ethanol, which is a co-solvent that allows separated water to mix with the fuel and purge as the fuel is consumed. If you suspect your system fuel system has water, the engine could operate poorly until all the water is purged.

The best additives to clean injectors are those with Chevron Techron.

One way to test the injectors is to swap them with other cylinders that don't show rich operation and clean or install new plugs. If the dirty plug condition follows the injectors, then you likely have an injector issue.

Duke
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  #5  
Old 06-15-2005, 03:39 PM
Lenny
 
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300e running Rich

It is possible that two of the fuel distributor chambers have failed. If you have the Manuals, you can check out the distributor with pressure gages.
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  #6  
Old 06-17-2005, 01:51 AM
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injectors

At first I thought it could be injectors - but however if theyre all original then they should all have the same wear ...should they not? So, from this I thought possibly the fuel distributor and more likely than injectors

That doesnt make sense does it?

lol
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Old 06-21-2005, 01:50 AM
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ok, have been away for a week and thinking about my plan of attack.

first thing i think is to swap the injectors round and see if the mixture moves with them. i hope so because the thought of having to buy a new fuel distributor is too depressing.

i'm also going to try and scrounge up something to test the fuel pressure to see how the EHA settings are.

Is there any way to check on the valve stem seals without removing them?

reports next week, hopefully
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Old 06-21-2005, 01:48 PM
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Quote:
Originally Posted by kiwi_bloke
At first I thought it could be injectors - but however if theyre all original then they should all have the same wear ...should they not? So, from this I thought possibly the fuel distributor and more likely than injectors

That doesnt make sense does it?

lol
No, injectors don't necessarily "wear" at the same rate, not do valve guides, cylinder walls, or piston rings. If you tear down an old engine you will normally find one or two cylinder walls worn noticeably more than the others. Same applies to valve guides. For various reasons identical components inside and engine don't wear at the same rate. One or two will wear a little faster and at some point the greater wear accelerates the wear rate until one or two identical components are significantly worn more than the others.

Rate of oil consumption is a good indicator of valve guide seal condition assuming the valve guides and rings/walls are not severely deteriorated.
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Old 06-21-2005, 06:46 PM
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.

well you learn something new every day I see you commented on testing the EHA settings. Wouldnt this affect the pressure at all injectors ?

Last edited by kiwi_bloke; 06-21-2005 at 09:15 PM.
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  #10  
Old 06-25-2005, 09:40 PM
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i've been away for a week and my mechanic checked the injectors while I was away. Turns out 1 and 6 weren't spraying correctly so he's changed them, which has improved the situation somewhat, the kangarooing has mostly gone although it still doesn't run smoothly at steady throttle, but now the car had developed a tendency to stall until its fully warmed up, so there's still cylinders missing at idle. also seems to be down on power at low revs.

plans today are to drop the fuel tank for a thorough cleaning - water seems to be getting in there and I want to know if there's a leak somewhere - and try to clean out the fue lines and system.

i also plan to adjust the EHA back a little bit. I think we may have overdone things while tweaking a few months ago. Cured the hot start problem but it may have contributed to the current problems.

i'd love to be able to check the fuel pressures myself but don't have access to a gauge. is this something I could buy or have made up, does anyone know?
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  #11  
Old 06-26-2005, 01:29 AM
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Try bleeding the injector lines at the fuel distributor. This really helped me with a past 190e 2.3.

It looked like the fuel distributor was bad and then a tech friend made the suggestion of bleeding at the distributor. A lot of crud came out and all of a sudden the car idled, it ran smoother than ever and the fuel economy shot up.

Haasman
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  #12  
Old 06-26-2005, 03:09 AM
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yes, have cleaned the injector lines at the distributor. this is something I do every couple of months, i would have hoped the fuel filter would clean most of it but the first squirt always seems to come out rust coloured, so there's obviously some corrosion somewhere along the line.

now in the process of cleaning the injectors, seeing as changing two of them has solved the running rich on two cylinders. have also obtained some special mercedes additive. don't know what's in it as there's no label but it must be strong, one capful is sufficient to treat 40 litres of fuel.

have also regapped the plugs to .9mm to see if that improves combustion.

mixture overall looked a bit weak, judging by the colour of the plug insulation. was grey on one side, blackish on the other. Not quite the nice biscuit colour I'd like to see but I'll run it a while and check again.
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  #13  
Old 06-26-2005, 04:51 AM
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Cleaned the injectors, now running smooth, low end power, no more driveline lash on the overrun, no more kangarooing. will add this task to the annual service plan.

however, the car always has the last word. just been to top up the petrol, added 40 litres plus a capful of the special MB go juice, now the petrol tank sender has spat the dummy and remains fixed on the less than 1/4 tank position it was before I filled up. if there's ever a day where everything works as it should, i'll stop and do a little dance in the car park.

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