MISSFIRE On My E420 RUNS LIKE CRAPOLA!!!

[Smokiesman]

My 95 E420 with about 133k on the meter gets a bug up its tailpipe and will start to run very rough almost like it is down to a 4 banger! At first it was just once in awhile but now it is happening more often. When I pull up to a stop it really smells of strong exhaust smell ? But not a rotten egg smell of a converter. Will miss at the low rpm but if I am in 1st gear and get the R's up if feels like the other plugs start to fire up! If I shut it down for say a hr. or so fire it up and runs like a clock? There was a post I think on this forum where a fella had simular problem and a member replied to it ! but do you think I can find that post?? I am taking car into the shop for new swaybars and shocks on Wed. and I wanted to to talk to tech about this prob and the members idea! Would like to find a solution to this as the car runs great otherwise! So if ya all got any ID whats going on hear I am all ears!

Smokie

[deanyel]

HAve you checked the fault codes? There's a number of things it could be - wiring harness for example. It sounds electrical/ignition related. My next step would be to see what the fault codes are saying.

[Smokiesman]

Thats the weird thing! no codes !! Makes finding prob all the harder!

Smokie

[bwheitman]

It sounds to me like it is going into limp mode due to a detected misfire. Check your plug leads, or replace them, did you recently get your engine wet? When I wash my engine it does this, restarting corrects it, but then if it misfires again it goes into limp. Of course as a 95 model you may have a harness issue as well, so check that out. You may need a new one.
Good luck!
Brian

[anziani]

I had the same problem on my '87 300E. We tried everything electrical and fuel related. My son in law casually mentioned that he had a similar problem on his Passat. It was the COIL! I couldn't believe a coil would misfire at LOW speeds. Changed the coil, solved the problem.
Anziani

[JimF]

Originally Posted by Smokiesman

My 95 E420 with about 133k on the meter gets a bug up its tailpipe and will start to run very rough almost like it is down to a 4 banger! At first it was just once in awhile but now it is happening more often. When I pull up to a stop it really smells of strong exhaust smell ? But not a rotten egg smell of a converter. Will miss at the low rpm but if I am in 1st gear and get the R's up if feels like the other plugs start to fire up! If I shut it down for say a hr. or so fire it up and runs like a clock? There was a post I think on this forum where a fella had simular problem and a member replied to it ! but do you think I can find that post?? I am taking car into the shop for new swaybars and shocks on Wed. and I wanted to to talk to tech about this prob and the members idea! Would like to find a solution to this as the car runs great otherwise! So if ya all got any ID whats going on hear I am all ears!
Smokie

Don't forget to check your cats? Also how about the dreaded "wiring harness"?

[alabbasi]

I had a similar problem on my 97 E420. It was only giving random misfire codes and trim codes. The car ran like crap and had zero power. When I tried to accelerate, the check engine light would flash. Long story short, it turned out to be a blocked cat. The code reader wont tell you if there is a problem with the cat but there are some diagnostic tools that allow you to read the live data from the O2 sensors before and after the cat which will give you an indication of what is going on. Hope this helps, it was very frustrating and expensive for me when I had this problem.

[Smokiesman]

Friend of mine thinks cats to! But I have hard time with that! This happens it seems like when I get in it and give her a hard blast down the the hwy! But I can shut it down for a short time it fires right up like nutin ever happened? Wish I could find that post ! Guy here had sameo prob. I think it is ign related because of the way it when it comes in it is like you hit a switch! Bang it goes! Then you drop the rpm and it runs like crapola again! I am not going to rule out cats just yet ! After reading ala's post , because the very first time it did happen the CE lite did come on ! but only the one time!

Smokie

[deanyel]

When you say no codes - how sophisticated was your code reading - the LED light, the homemade code reader, a scanner? It seems like it must be putting off some kind of code somewhere.

[Smokiesman]

I used the led one up by the firewall! nada zero zip!!

Smokie

[deanyel]

That's only the emission related codes - you need to check the 38 pin connector - I'll bet you find something that will offer a clue.

[suginami]

Have you replaced both of your distributor caps and rotors.

I've seen the exact same symptoms on a '93 500SL (same engine) that limped into my Mercedes tech's shop.

[Smokiesman]

ozzy's Avatar
ozzy ozzy is offline
benz tech

Join Date: Dec 2004
Posts: 170
The engine control module in your car constantly monitors engine performance, so if any cylinder has a misfire due to bad sparkplugs, defective coil or any other reason, the engine control module will shut that cylinder down via injector cut, turn eng off and back on will reset eng control module.

The main reason for this is to protect the cat from raw fuel entering and causing a melt down.

First thing I would suggest is doing a basic tune up, replace spark plugs, inspect coil ends and plug boots for any sign of moisture or arcing, air filter and fuel filter if you are confident in doing so.

Failing that I would suggest having it scanned for fault codes, this will lead you in the direction of your problem.

Then you could post results and we could try to advise with more specific information.

ozzy.




This is the post I was looking for ! Kind of leanin in this direction.
another guy suggested the OVP relay! have not ruled out cats yet!


Smokie

[suginami]

Originally Posted by Smokiesman

another guy suggested the OVP relay! have not ruled out cats yet!


Smokie

E420's do not have OVP's.

Did you read my above post about your distributor cap and rotor?

M119's are very hard on these items, and they rarely go over 100,000 miles without failing.

[Smokiesman]

Been givin the idea plug cap and rotor replace in the VERY near future! after going through records last nite the only thing I saw as far as tuneup was plug replace! Most likley due for replace would not surprise me if orig! and with 133k would say its time! Thanks for the heads up on the OVP!!

Smokie