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Discussion Starter #1 (Edited)
Greetings W210 forum members,

I purchased a 97 E420 Sport a few months ago, had no problems and engine ran nice and smooth overall until now, current mileage is around 150K.
All of the sudden just overnight, engine won't rev past around 3,000 RPM accompanied a blinking CEL if trying to rev past 3K.

I've read many of the relevant threads here through searching, none of the descriptions seem to fit quite the same.
Idle is smooth and accelerating up to 2,000-2,500+ RPM seems smooth and normal with no vibration or shaking in any gear.

I've checked the spark plugs and wires recently, they looked normal upon visual inspection.
The following 5 diagnostic codes pulled are posted below in the order retrieved.

P0305 Cylinder #5 Misfire Detected
P0306 Cylinder #6 Misfire Detected
P0308 Cylinder #8 Misfire Detected
P0307 Cylinder #7 Misfire Detected
P0300 Random/Multiple Cylinder Misfire Detected

Before we start throwing parts at it, any ideas what may all of the sudden cause misfires on all four cylinders one the same side?
Any helpful feedback from fellow members is highly appreciated.

Best Regards, Ken
 

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O2 sensors or blocked cat maybe the problem on the driver side ... worth to look into. It is recommended chenging O2 sensor around 100k miles .... however, I think is the Cat ...
 

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Discussion Starter #4
O2 sensors or blocked cat maybe the problem on the driver side ... worth to look into. It is recommended chenging O2 sensor around 100k miles .... however, I think is the Cat ...
Interesting, thanks for suggesting the cat as I've read it's somewhat common for the 97 E420.

This is unheard of for my 95 SL500 as we have only one catalytic convertor.
 

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Thanks for the reply, were the detected multiple misfire cylinders all on one side?
I can't remember what cylinders exactly were affected but it also showed up on my climate control that my alternator was only charging 11.0, short of the regular 13 volts.

Also accompanying it was flashing CEL and flashing traction light (the exclamation point in center of the speedometer)
 

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Disconnect the driver's front cat - like whaaa is that ?

To test the cat they put up on a lift, and do a rubber mallet test tapping and listening for rattles caused by break down of the internal cat element AND they take a IR thermeter and measure if rear exit temp is significantly higher than entrance temp on the cat indicating correct efficient operation.

If a cat is "bad" then break down of internal cat element starts exhaust blockage/restriction that chokes off that side.

If cat needs replacement other than California you can use generic equivalent cat for front replacement, also if front cat goes bad, best to have rear cat shaken out and cleaned overnite too - where the broken pieces of the front cat end up.

Keep the beat !
 

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Discussion Starter #11
Probably take the E420 to a local muffler shop and have them disconnect the driver's side front cat for further testing.

Will keep you folks posted with my findings, thanks for the good luck wishes.
UPDATE:

I had the muffler shop disconnect the driver's side catalytic converter piping at the front and loosened the rear bolts.
Drove her down the road and the low RPM cutoff issue was gone, evidently back pressure from a clogged cat was the culprit.

Both driver's side cats will be replaced with a Catco direct-fit aftermarket unit.
I was quoted $663 for all parts and labor/installation with tax, will post back with further details.
 

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UPDATE:

I had the muffler shop disconnect the driver's side catalytic converter piping at the front and loosened the rear bolts.
Drove her down the road and the low RPM cutoff issue was gone, evidently back pressure from a clogged cat was the culprit.

Both driver's side cats will be replaced with a Catco direct-fit aftermarket unit.
I was quoted $663 for all parts and labor/installation with tax, will post back with further details.
There are aftermarket ones that will work for about 1/4-1/3 that price but they would have to be welded in. The various other aftermarket (DEC and Eastern in addition to the one you mention) are fine as well. Germanstar stocks some of these too.

(Sorry I just got your PM this morning and finally had a chance to look at the thread.)
 

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Discussion Starter #13
There are aftermarket ones that will work for about 1/4-1/3 that price but they would have to be welded in. The various other aftermarket (DEC and Eastern in addition to the one you mention) are fine as well. Germanstar stocks some of these too.

(Sorry I just got your PM this morning and finally had a chance to look at the thread.)
Hi Greg, thanks for chiming in on the topic, I sincerely appreciate your advice as always.

They have already started on the repair order, I'm told the E420 will be ready for pickup tomorrow morning.
 

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Have them pull the rear cats - those rears are basically cans with internal screens - and shake out any debris caught back there at the screens - there is usually debris caught back there from the degraded front cats.

As long as the screens are intact they are recoverable.

Some shops who do top work pull them them the night before - shale and blow them out - then soak overnite in a bucket with water/dishwasher soap mix - then blow them dry in the morning for the zip up.

Very good time to check your engine mounts - I would say a bit more than 40% of the cat failure I have seen in W210 has been acclerated/caused by at least one failed mount. If mount needs replacement Sachs/Boge is OE mount over the cheapie-China mounts that don't last long at all.

Keep the beat !
 

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Discussion Starter #15
Have them pull the rear cats - those rears are basically cans with internal screens - and shake out any debris caught back there at the screens - there is usually debris caught back there from the degraded front cats.

As long as the screens are intact they are recoverable.

Some shops who do top work pull them them the night before - shale and blow them out - then soak overnite in a bucket with water/dishwasher soap mix - then blow them dry in the morning for the zip up.

Very good time to check your engine mounts - I would say a bit more than 40% of the cat failure I have seen in W210 has been acclerated/caused by at least one failed mount. If mount needs replacement Sachs/Boge is OE mount over the cheapie-China mounts that don't last long at all.

Keep the beat !
Thank you for the recommendations, however the rear cat alone cannot be pulled unless cut out.

It is all one piece welded together inline with the front cat.
 

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Ken,

I am glad that your problem is resolved and thank you for the updates since it would help our members with similar issues. The key to the quick trouble shooting was your post which had all the relevant information that one may need to make a recommendation.

Take care.
 

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Yeh, the rears get cut out and welded back... they can do a mallet test on the rears to listen for big chunks.. or you can see down the road after the fronts have been replaced .. maybe 25% of the time rears stay a probklem... all depends on the amount and size of the checks that got thrown back..

Keep the beat !
 

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Ken,

I am glad that your problem is resolved and thank you for the updates since it would help our members with similar issues. The key to the quick trouble shooting was your post which had all the relevant information that one may need to make a recommendation.

Take care.
Plus one. He gave detailed information, you pointed him in the right direction and then the thread unfortunately got sidetracked.

Whatever curious and odd exception might have been an issue for one person, the old rule still applies: If it walks like a duck and sounds like a duck and looks like a duck, it's probably not a marmot. ;)

Neoken, I'm glad you got it fixed (in the way that made the most sense to you overall), but mostly that you got it diagnosed and fixed correctly the first time around. Now you can get back to enjoying the ride!
 

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Discussion Starter #19
Neoken, I'm glad you got it fixed (in the way that made the most sense to you overall), but mostly that you got it diagnosed and fixed correctly the first time around. Now you can get back to enjoying the ride!
Greg, since it's our primary family car, believe me I'm very grateful that we were able to diagnose the issues at first attempt.

Like most of us probably know, worst things can happen with a Mercedes 15 years of age.

Anyways, I got the car back earlier today, cleared the existing diagnostic codes and been driving around this afternoon with no CEL. (Approximately 50 miles)
As a bonus, a clearly noticeable increase in overall torque (especially low to mid-range) and throttle response present in addition to restoring above driveability issues.

Hopefully this topic helps the next individual diagnose similar symptoms of one or more clogged catalytic converters.
 

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Discussion Starter #20
Ken,

I am glad that your problem is resolved and thank you for the updates since it would help our members with similar issues. The key to the quick trouble shooting was your post which had all the relevant information that one may need to make a recommendation.

Take care.
Many thanks Eagleone, your original suggestion was accurate and very much appreciated. :thumbsup:
 
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