Missing at low RPM.. - Page 2 - Mercedes-Benz Forum
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post #11 of 14 (permalink) Old 11-15-2016, 07:36 PM
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Symptoms

Quote:
Originally Posted by Rotorguy View Post
I did pull and check all the the plugs. They are the correct F8DC4. All looked OK...one had a carbon black tinge to it. But one also had a raw fuel odor to it.

To-day, all day, it has been perfect. No hesitation..purrred at stop lights around 600RPM and responded instantly to the accelerator.
But, tomorrow...well, that's tomorrow. You never know.
This is simple to evaluate.
Carbon black on a plug = fuel fouled. MISFIRING badly.
Raw fuel odor on a plug = flooding. MISFIRING badly, injector leaking.

You can spend HOURS troubleshooting items, but dollars to donuts it is as simple as wires. Focus on those two cylinders, check the ohms on those wires compared to a good cylinder or two.
I'd say the caps are getting moisture in them as a possibility, but you say you changed those. Did you change the o-rings on the caps? What did the old caps look like? White crusty powder on the posts? Black soot?

Today runs perfect, the next not so well. WHAT WAS THE WEATHER BOTH THOSE DAYS?? Temp, humidity? How long does it sit between drives?

I still don't know where you live or the mileage of the vehicle. When was the last time you replaced the wires?

Could there be other causes? Certainly! But those two plugs are telling.

If you suspect the injector seals are an issue, carefully spray some starting fluid or WD-40 around the injectors to see if the engine revs indicating a leak.

GSXR is an expert, I'd do as he suggests. Tutte is no slouch, either. I'm just a hammer mechanic, but I've owned hundreds of cars, and seen these symptoms quite often.

If money is an issue, try junkyard parts if you have access, at least to help diagnose the simple stuff like wires. MB just quoted me $439 for new wires, YIKES!
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post #12 of 14 (permalink) Old 11-16-2016, 03:18 AM
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Not a good idea to use starter fluid on injector seals . Its known to disintegrate the rubber seals WD40 is much more forgiving ..
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post #13 of 14 (permalink) Old 11-23-2016, 02:18 PM
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Have Eco-Junk wires been ruled out?

Dates on harness and ETZ will tell all on these.

My 400e never ran right until I got post '97 wires and ETA
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post #14 of 14 (permalink) Old 11-23-2016, 02:25 PM
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Oh yeah....they've been changed.
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