97 E420 feels strangled over 4500 rpm - no codes - PeachParts Mercedes-Benz Forum

apb · #1 05-28-2011, 11:36 AM

Any thoughts? I replaced the sparkplugs and it made no difference. Car has 180kmi and mass air sensor/ O2 sensors were replaced 10kmi ago. I do not drive the car much any more and this seems to have crept up, but I could be wrong.

daddi · #2 05-28-2011, 02:56 PM

This might be a transmission problem. Check the transmission control unit for transmission fluid or the transmission overload circuit.

rjk · #3 05-29-2011, 11:23 AM

Just for giggles, tap the cat converters to see if there is a rattling noise in either. I started getting high speed deformance (is that a word?) which devolved rapidly into the car being barely functional. It was a plugged CAT. They seem to start failing when they go north of 100k mi.

apb · #4 05-29-2011, 07:33 PM

I will need to check that. Would I not have gotten a code if the convertor had failed?

rjk · #5 05-29-2011, 09:21 PM

I didn't when mine failed. It was this forum that pointed me in the right direction.

apb · #6 05-29-2011, 10:14 PM

forgot to mention I had oil in the ignition coils as well on the right side (just replaced the valve cover and plugs to fix that). seems to point to some issue on the right side of the engine. I assume it might have to do with some pressure backup issue. It looks like you have the same problem.

What brand convertor did you end up going with?

I also researched how to test failed convertors and saw some interesting information about testing with an IR temperature sensor (which I already have). I will test tomorrow.

rjk · #7 05-30-2011, 07:48 AM

Exhaust back pressure won't cause an oil leak. The two are unrelated. You really only need to rap the converters with a mallet, if a CAT is deteriorating, it will rattle. Although I guess out of whack temp rises & drops could point to a failing CAT, listening for a rattle is quicker.

apb · #8 05-30-2011, 11:47 AM

Ok, I am sold... was it your front cat or rear cat that failed? Front cat failure should trigger codes, rear would not.

alabbasi · #9 05-30-2011, 12:15 PM

Catalytic converters are known to block on these cars.
There's also a big vacuum hose going to the air mass sensor that turns into mush. When I replaced mine, it felt like the car gained 100hp.

rjk · #10 05-30-2011, 03:13 PM

First CAT.
No code for me.

I'm not saying definitively that it is your CAT, just something to check based on the similarity of a problem I had last year.
My car bogged down on the highway at speed.
Then it got to the point (over a few days) where it would not run at speed.
After a short layover of about an hour, it restarted & ran fine for about a week.
Then it coughed & died & would not run over 20 mph.
I initially assumed ignition since there was oil present on most of the coils & it was due for a tune-up which I performed (removed & cleaned coils, R&R plugs, etc). No joy.
This forum pointed me to the CAT stating classic symptoms, they were right.
Knocked on CAT, it rattled, removed it & the car was back to normal.

Your bog at speed is the only similarity so far but is worth knocking on the CATs to see if either one rattles. They are not cheap and there are two (rt & lft). It is the forward CATs that seem to fail & block things up. The dealership will probably recommend replacing both. That can run north of $2k so you don't want to go and purchase something without confirmation (rattle).
I found some Bosals for about $600 on the web, it isn't a hard R&R. I did it on my back in the driveway w/the car up on jackstands. I did not replace both but am expecting the other to fail. At least this time I will know the preliminary symptoms & can catch it early (I hope).

whunter · #11 06-19-2011, 02:56 AM

Quote:

Originally Posted by apb

Any thoughts? I replaced the sparkplugs and it made no difference. Car has 180kmi and mass air sensor/ O2 sensors were replaced 10kmi ago. I do not drive the car much any more and this seems to have crept up, but I could be wrong.

What was the problem?

Has it been fixed?

How much did it cost?

apb · #12 06-19-2011, 03:09 PM

it was the right cats section which was plugged. got oem mercedes cats assembly from ebay for $550 - great deal. had it installed at Midas for $160 - another great deal. got the car back yesterday, it runs perfect again.