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2009 ML320 & 1984 190D
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229 Posts
Discussion Starter #1 (Edited)
Have a 1990 190E 2.6 with 91,000 miles.
Runs great, and did 26mpg on a round trip on the freeway around LA with the AC on...
Failed smog the first time and even got a nice GP stamp.



Did a full work up on it...
Fresh oil and filter, Correct Non resister plugs, New cap, Rotor, Fuel filter and OVP.
Tested plug wires and they look new and all tested good.
Compression test shows between 170/175psi across all 6 cylinders.
Reset Duty Cycle to 50% at idle and its close to within 10% at 2000rpm.
Tested fuel pump output and FD output at each injector.. all way within spec.
Tested operation of EGR at valve using Mityvac and can see it open and hear the engine note change.
Cat is not the original, but looks newer.

Engine starts first time, hot or cold, and runs sweet... but does feel a little sluggish at off idle at lower revs.

Took it back for a Smog at a different place and they said they would "Pretest" it.
Failed again....
Because they did an Idle test, I am not sure if the results are comparable.... But the O2 was up slightly and the HC was down at the higher revs...



Don't have a ton of $$$ to throw parts at it...
I am puzzled why the O2 is high.... O2 sensor, or Cat?

Opinions or insight please!
 

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Registered
1991 190e 2.6 automatic
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760 Posts
its your cat it probably died prematurely since these cars burn oil more than newer cars and that cat was a universal one probably.
 

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Registered
2009 ML320 & 1984 190D
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229 Posts
Discussion Starter #3
Its possible.
I tested the cat today with an IR Thermometer.
Looks like its lighting off fine.
 

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Registered
1991 190e 2.6 automatic
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760 Posts
Its possible.
I tested the cat today with an IR Thermometer.
Looks like its lighting off fine.
well even if it checks ok, you still dont know if its killing enough of the gases or not coming from your car.
 

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2009 ML320 & 1984 190D
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229 Posts
Discussion Starter #5
Update...

The car runs great, starts first time, and runs strong...
Upon testing the O2 sensor, I felt it was slow to respond...


Here are two video links showing the tester before and after, with the Duty cycle readings for reference at idle(I had it set at 30% because I was trying to get the best balance between rich and lean... I later put it back to 50%)


And at 2500rpm with the same duty cycle..
The cycling is faster, but I my gut said it was sluggish.



I replaced it...
Now look at the diffence at idle..
Duty clcle was reset to 50%, and look at the snappier response and wider voltage swings between rich and lean.


And at 2500rpm..
 

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Registered
2009 ML320 & 1984 190D
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229 Posts
Discussion Starter #6
Feeling confident, with the new O2 sensor in, everything was feeling good!

Took it back for a Pre-test....
It failed again on HC at the lower speed...
Oh, and just for good measure to give me a kick in the nuts, between the morning start and the smog station... the CEL bulb blew, adding a visual failure to the insult!
The reading were pretty similar... failed at lower engine speed...



I got under the car...
I had not done this before, but I banged the Cat... which is not the OEM unit...
It rattled...


So, I decided to replace it..
Here is CA, its not so simple or cheap...
But here it is... the correct magnaflow CARB approved cat..


Cut the old one off today...
The pictures will speak for themselves....



I am feeling like that could be the issue!
 

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Premium Member
W-1-2-3 Go!
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16,161 Posts
Look for items that could cause the catalytic converter to fail as a precaution.

High NOx would probably indicate a bad catalytic converter too. But check to make sure your engine is performing a complete burn of the HC's before it goes out the exhaust.

Also check the pre-cats if your car is equipped with any. They could also cause a failure.
 

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2009 ML320 & 1984 190D
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229 Posts
Discussion Starter #8
Thanks, I will be looking.
The Pre-cats are gone, the front part of the exhaust was replaced some time ago... the date stamp on the junk cat was 2006.

I was told that the valve seals have been done, but will watch the oil consumption closely. The plugs that were in it when I got it, even tho they were Resisters, looked fine.
Original plugs...



And I know how the valve seal go, even on a low milage M103...
This is a plug with about 1000 miles on it from my Son's 68k mile 300TE...


And the set...


So I have done 3 sets of valve seals in my time... so far!
 
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