"Old Pearl" failed emissions - David Poole, HELP - PeachParts Mercedes-Benz Forum

S-Class Guru · #1 07-31-2007, 06:22 PM

Well, the old '91 300SE finally failed the Dallas emissions test, HC and NOx at low speed. It passed at the high speed test.
Below are the gory details.
If bored, please skip to the last sentance, that is my big question, I guess.

25MPH 15MPH

HC 108 97 112 173 (fail)
CO% 0.60 0.16 0.62 0.31
CO2% 14.8 14.4
O2% 0.2 0.5
Nox 751 453 829 1171 (fail)
Dilution >6 15.0 >6 14.7

Last year she passed with readings approx 1/2 the limit, and not a lot has changed in the way she runs.
So, I think I'll try the following?

1. Clean the EGR line. (been awhile).
2. Double-check for vacuum leaks. But I just replaced the IAC hoses awhile back, all hose connections are tight, and the injector seals are pretty new - vacuum at idle is 16".
3. Top-end cleaner (Seafoam).
4. Fill up with Super Chevron (been running midgrade Chevron lately).
5. Change the oil (but it's pretty new).
6. Change air filter. Plugs were brand new when I failed today.
7. Recheck the Lamda duty cycle, but it was at 48-52% and fluctuating well just last week.
8. O2 sensor is original, but seems to be working ok, per the duty cycle monitoring. David monitored the sensor on his cool equipment last month, seemed ok then. At 17 years maybe I just ought to change it?
9. Drive the crap out of it before taking it in.
10. ??? anything else?

Would the Lamda setting affect these emissions? Mine is dead-center at 48-52% and moving well, per my Sears duty-cycle meter. Seems to me, if the Lamda were lowered or raised a bit, the sensors would take over and move the mix to Stoi anyway. But would changing the duty cycle actually change the closed-loop mixture, and the various emissions levels? if so, should I decrease or increase Lamda percent to improve the HC and NOx readings?

Thanks,
DG

S-Class Guru · #2 07-31-2007, 06:27 PM

Darn, my nice chart got all crammed together.
I was trying to set it up as:
25mph limit, 25mph read. 15mph limit, 15mph read.

Anyway, failed 15mph HC and NOx, not excessively, but decisively.
Any ideas?

DG

just-n-time · #3 07-31-2007, 08:53 PM

David's#214 956 7007

mbdoc · #4 08-01-2007, 08:45 AM

If you pull vacuum on the EGR valve with the engine running, do you see the engine start to run rough? IF not then the EGR system might be the problem

bpaz_ph · #5 08-01-2007, 11:04 AM

One or two of your cylinders have poor combustion. I'd start with the plugs to see if any are unusually dark or wet.

david s poole · #6 08-01-2007, 11:06 AM

dg,give me a call and save wear and tear on my typing finger.

bpaz_ph · #7 08-01-2007, 11:07 AM

Oops, I see you changed the plugs. Were any of the old ones unusually dark? Also, how are your ign wires?

S-Class Guru · #8 08-01-2007, 01:00 PM

Thanks, guys.
If I could rework that tranny, surely I can get this engine to pass One More Time.
- I checked out the EGR. the pipe is clear, and if I bypass the solenoid and hook vacuum directly to the valve, the valve opens fully and the engine really stutters. Can't tell a lot about the solenoid by just revving in neutral, I guess it's controlled by the computer. But I can get it to energize for a few moments by playing with the throttle, so it seems okay.
- Yeah, all my plugs get pretty dirty after 15k miles, particularly #1.
But nothing real serious, just the usual carbon on the ground area.
#1 is down on compression about 10-15 pounds below the others, but it's been that way a long time.
- She's always been pretty dirty; I remember a couple of yeasrs ago I passed a 112 limit with a 111 reading.

David, I'll give you call.
tks,
DG

EricSilver · #9 08-14-2007, 01:00 PM

Quote:

Originally Posted by S-Class Guru

1. Clean the EGR line. (been awhile).

I would be very interested in this. I passed my Virginia test yesterday, but with higher numbers than two years prior.

HC was 65 of an allowable 125(?) and NO was 0.17 of an allowable 1.00. Two years ago, HC was 7 and NO was 0.00.

The CEL has been illuminated for two years, with a 5-code at the DM. Would a clogged EGR tube cause this type of variance in emmissions results?

Also, the car was running quite hot before the test (after a long commute and extended idling at the inspection station) -- to the point where you start to smell that pungent, acrid aroma from the exhaust.

Could whatever was burning in the fuel have contributed to the elevated HC? The guy at the inspection station revved the engine for a few minutes (while reading the sports section of the paper) until the acrid smell was largely gone, before doing the test because, according to him, 90% of the E320s/W124s he tests Fail the first time. I am assuming this is because of the engine running hot and burning some otherwise stable fuel addititives, which causes the acrid fumes, and skews the tests.

Or is it a (temporarily) backed-up catalytic converter effect?