94-E420- Running Rough after one day sitting

After my MB E420-1994 sits for a day, it starts up fine and runs perfect for about 15 minutes, then start to run rough (rotten egg smell) for about 3-5 minutes then runs perfect after that, all day. It
runs great as long as I run it a couple times a day. Not sure what's happening? I replaced oxy sensor, no change. What are the symptoms of a bad catalytic converter? I had a fuel line leak (line attached to filter) that I patched, could fuel pressure drop cause temp rough run? any help would be appreciated....
Thanks, Derf
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Yes, fuel pressure leak will cause hard hot start problem. Say, you went to a store and came back to your car after 15 minuted, the car struggles to start and if you got it started, it ran very rough.
That fuel leak you have, you need to replace that copper washer to fix the problem. If it still leaks, then you need to use aviation form a gasket and coat both side of the copper washer.
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Thanks Tiger,
The fuel line leak was in the hose- I wrapped it with Teflon tape and gasket seal combo... it was spraying a fine mist and my fix stopped it. Car starts up OK after it starts to run rough or sits.
Derf
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Replace that hose... it will drain your fuel tank so do it when the tank is low... or suck the fuel out into containers.
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I really can't tell why it runs fine for the first 15 minutes and then has a "blackout" for a couple of minutes before running fine again.
After 15 minutes, the engine itself has reached normal operating temperature, and all should be settled there. The engine compartment will heat up slower, and possibly something there is sensitive to heat, possibly due to collection of moisture when engine stands still for at period (and evaporates when heated by the engine). I had once a small crack in the ignition coil, which gave unpredictable symptoms like yours.
Anyway, as Tiger says, you should under all circumstances replace the piece of fuel line. It is under high pressure and not worth the risk.
A drop in fuel preassure due to a small leakage can cause hard starting (mostly in hot weather conditions), due to evaporation of fuel in the fuel system. But once started it would not cause rough running after 15 minutes, unless the leak is so heavy, that you can't avoid noticing it.
A defective catalytic converter would normally not affect the engine running, unless comletely pulverised due to overheating (too lean mixture) causing blocking of the exhaust system (happened to me). That results in lack of power, not symptoms like yours.
The smell of rotten eggs indicates overheating of your catalytic converter. Possibly this is due to bad air mass sensor (as I had). If that is the case, you should get it fixed immediately before blowing the catalytic converters (then it becomes really expensive).
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The more I think of it, the more I believe this is your problem. Take care.
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Could it be that when the car sits one day without running, air mass sensor (AMS) cools completely, then when car is started is runs fine until air mass sensor reaches operating temp then malfunctions (it thinks car temp is still cool and runs car lean which causes rough operation and egg smell, keeping fuel delivery in cold start mode) eventually the air mass sensor adjusts to correct temperature reading (the longer car sits the longer the car runs rough and rougher)? Is there a check engine code for the air mass sensor? and where is the so- called existing code reader button located, I read somewhere? Can you clean or check AMS? Would an air filter assembly leak where AMS connects cause rough running? Sorry about all of the questions, but I truly appreciate all help... thanks...Derf
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Pretty much yes to all. Do you have a check engine light on at this time? If yes, pull the codes.
Air leak dramatically affect the driving condition.
Dirty MAF or failing MAF will cause problem too. Clean the MAF with MAF cleaner... not carb cleaner.
Make sure all connection is tight.
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In addition to to Tigers answer:
MAF does not do any "thinking" - it simply measures the airflow through it. The ECU (Electronic Control Unit) does the thinking. It gets temperature information from sensors near the water pump, and together with air flow and other information it controls the amount of fuel injected into cylinders together with the air.
Air filter sits before the air mass sensor, so a leak here will not cause rough running. But any leak in the intake manifold system (including vacuum lines) would cause rough running.
What puzzles me is the time scheme (15 minutes OK, 4 minutes bad, then OK again... all depending time since last warm). That does not point at a vacuum leak (bot does not preclude it either).
Your last information of the dependence on time since last operation strongly points at a moisture problem. The question is where. That guides me to a well known Mercedes problem: The insulation in the engine wiring harness is made of a material, which will degrade by time, particular in hot areas of the engine compartment. It is easily noticed as cracking insulation, when you expose the wires in the harness. That would definately make symptoms as you describe possible.
So, check that.
A new harness is easily replaced and cost about 700 USD.
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I was going to suggest a day or 2 back that it could be a defective temperature sensor - if such a thing can happen in a Mercedes - not telling the ecu that the engine is getting warm until several minutes after it should ????
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