E420 random cylinder misfire
06-05-2009, 08:48 PM
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E420
E420 random cylinder misfire
I have a 1997 Mercedes E420 with 140K miles that is acting up. Recently it started to idle rough and has a very distinctive loss of power. I pulled the engine codes and I am getting P0305, P0306, P0307, P0308 and P0300. I take that as I am getting random misfires on cylinders 5-8 only. I have changed the spark plugs (all 8) changed the spark plug boots on cylinders 5-8 and also changed the coil packs on cylinders 5-8. Still the problem exists. I pulled the spark plug on cylinder 5 and started the engine and there is indeed a spark. I pulled the injectors and they "look" okay. If I pull the connection to any of the injectors, a noticeable engine change is noted.
I searched these forums and I have already tried most of the suggestions with no luck. Further thoughts if it were bad gas, why would only cylinders 5-8 be affected? there is a ticking coming from the engine which could be the oil feed tubes but would that case a misfire on all cylinders on the drivers side? A clogged Catalytic converter could also cause problems but would that only affect cylinders 5-8?
Any ideas of what to try next. The trial and error approach is getting a bit expensive so I am looking for any advice. Is there some sort of module that controls the ignition coils on each side of the engine that could be malfunctioning?
Thanks in advance for any advice/suggestions.
I searched these forums and I have already tried most of the suggestions with no luck. Further thoughts if it were bad gas, why would only cylinders 5-8 be affected? there is a ticking coming from the engine which could be the oil feed tubes but would that case a misfire on all cylinders on the drivers side? A clogged Catalytic converter could also cause problems but would that only affect cylinders 5-8?
Any ideas of what to try next. The trial and error approach is getting a bit expensive so I am looking for any advice. Is there some sort of module that controls the ignition coils on each side of the engine that could be malfunctioning?
Thanks in advance for any advice/suggestions.
06-06-2009, 08:15 AM
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03 E500 and Corvette
If after checking for plugged cat. (I have never had a plugged cat cause only 2 cyls missfire. It really cuts power and performance but not exclusive to specific cylinders.)
I would do a compression check/balance by doing the wet / dry compression checks.
This sounds like there might be low compression since you have changed all the ignition parts associated with 5 and 8. These cylinders don't share a common cylinder wall. I suspect valve issues.
You mentioned clicking noise. I suspect a valve is being held open, burned or lifter leakdown. Before spending any more $$ I would get the information on condition of the engine.
I would do a compression check/balance by doing the wet / dry compression checks.
This sounds like there might be low compression since you have changed all the ignition parts associated with 5 and 8. These cylinders don't share a common cylinder wall. I suspect valve issues.
You mentioned clicking noise. I suspect a valve is being held open, burned or lifter leakdown. Before spending any more $$ I would get the information on condition of the engine.
