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....
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.
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.
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
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).
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
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.
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.
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 ????
Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here.
All logos and trade names are the property of their respective owners.