M104 Smog Failure Troubleshooting - PeachParts Mercedes-Benz Forum

NosserW124 · #1 11-19-2014, 08:20 PM

Hey everyone, long time lurker, first time poster.

Hoping someone might be able to point me in the right direction on figuring out how to get my '94 E320 back in the good graces of the state of California. 138k on the chassis, with an 80kish engine that replaced the original unit that suffered a catastrophic HG failure (before it was under my care.) Went to smog today and got the bad news - gross polluter. Here are the numbers:

15mph - %CO2 8.5, %O2 0.0, HC Measured 342 (max allowable 57), CO% Measured 9.84 (max allowable.47), NO measured 52 (max allowable 478)

25mph - %CO2 13.8, %O2 0.0, HC Measured 180 (max allowable 32), CO% Measured 1.51 (max allowable.44), NO measured 62 (max allowable 484)

Both were conducted at approx 1600 rpm.

So I'm sky high on HC and CO% at both speeds, but better at more load, and very low on NO in both scenarios.

I'm a pretty accomplished wrench, but beyond clueless at interpreting this data to suggest a repair path. Any ideas would be greatly appreciated.

oldtrucker · #2 11-20-2014, 12:01 PM

So, the CEL is lit, I take it.
First of all, I was told that the dyno test is not correct for this model, don't ask why.
According to the book of wisdom, the test can be performed either on the dyno or at no load e.g. at idle and 2500 RPM. In any case your numbers are out the roof, so it doesn't matter.

I had similar smog results with my 95 E320 and it turned out, to make a long one short, to be the O2 sensor. The O2 sensor had about 1/32 of carbon deposits on it and therefore was lame and low in numbers that was send to the ECU.
You simply could remove the O2 sensor and start checking there, visually that is! Use a 22mm wrench or Oxygen wrench. Fairly easy to get to it.
If it looks carboned up, replace it and do a smog pre-test only. Some smog stations offer it and do NOT send any results to the state, if it fails. The O2 Sensor is running anywhere between http://www.amazon.com/Bosch-13314-Oxygen-Sensor-Fitment/dp/B000BZI1J6/ref=sr_1_35?ie=UTF8&qid=1416503846&sr=8-35&keywords=Mercedes+O2+Sensor $80-$250 depending on where you shop.
It is probably better to purchase the direct replacement with the correct connectors on it, even though the universals are much cheaper.
There is a chance that your CAT is fouled up too, depending on the previous engine failure. Then it gets into the hundreds, there are aftermarket replacements, but the rumor is that they don't last as long as OE. Aftermarket goes for around $300.00 and has to be CARB approved for California.

Otherwise, the engine appears to be running fine?

Also, the CEL may need to be cleared after the replacement and a few trips should be done before testing again.
If it still fails, then come back and post, we'll figure something out.
If it passes, please post the outcome too.
Good luck!

NosserW124 · #3 11-20-2014, 02:18 PM

Thanks, trucker! Given that it's more than likely due anyway I just ordered an O2, it's on its way.

I did pull codes last night with the magic button (it's a CA emissions car) and its throwing the following:

10 - Voltage at hot wire mass air flow sensor too high/low
20 - Speed signal not present

So I'm thinking at the very least I need to clean the MAF to try to remedy the first, no clue on the second.

NJ300sdl · #4 11-20-2014, 08:19 PM

My 1991, CIS, M104 passed NJ emissions test by running on 45% alchol. Then found the reason for the failure, the cats were empty because of age. Replaced them.

oldtrucker · #5 11-21-2014, 01:47 AM

Hi NosserW124,

Quote:

I did pull codes last night with the magic button (it's a CA emissions car) and its throwing the following:

10 - Voltage at hot wire mass air flow sensor too high/low
20 - Speed signal not present

Cleaning the MAF/MAS could do the trick, however, they have electronics built in e.g. at least an OPAMP. Technically this is not going to fail as long as it doesn't get abused.

Depending on brand or country of origin, the Hot Film may not be there and is replaced with a resistor and a wire. They work the same, are a lot cheaper than the OE part, but may have larger tolerances, some people don't even want to touch them.
I found, that the low cost MAF's are already putting out some voltage without airflow. Also, they can be electrically noisy, which is probably due to the low quality of OPAMP's in the circuit. (Sheep, sheep, sheep)

Is your speedometer needle jumping large distances?
If it does, the speedometer cable may not be seated properly at the gearbox end or it simply got kinked.

My second guess would be the speed sensor (Hall Sensor) mounted on the backside of the instrument cluster.

On the other hand, these codes don't cover the high CO and HC values, they would trigger for sure an open loop code, adaptation impossible.

Did these codes possibly come from pin 3 e.g. built in LED

Quote:

magic button

Or do you have a LED Count Reader and got them from Pin 8 (Pin 14 got only 15 codes for this model)?

HFM (Pin 8):
<20> Self-adaptation at idle speed or upper/lower partial load at rich or lean limit.
<10> O2 Sensor (after TWC)voltage too high, circuit open or voltage implausible
would make sense.

I always get confused with this mix and match stuff and if it is that then this or that etc. plus digital or analog.

I think cleaning the MAS and replacing the O2 Sensor will get you somewhat ahead, if not fixing it.

oldtrucker · #6 11-21-2014, 02:31 AM

NJ300SDL,
yep, the constant heat can burn them out, I heard that a piece of catalytic converter, started a wild fire in San Diego county, this year.
I believe, because of the different climate, they have to be CARB approved and possibly more resistant at higher temperatures? Dunno that for sure.
But there are people that swear on the OE for our W124.032 and my cat has now over 220,000 miles on it. The CO content was measured at 0.02% last year. Also, many people overlook that fact that a cat, takes out only 1-2% CO. My guess, many times they are replaced un-neccesary, but can be destroyed within a few seconds, if the engine blows the wrong stuff through it. So it is very important to keep an eye on emissions!
Not in your case, if it was empty...

NosserW124 · #7 11-21-2014, 02:47 AM

Yes, the codes were read from the LED. I'm not able to pull codes from pin 8 as I don't I don't have a code reader.

Regarding the speed signal fault, that one was a real puzzle to me - speedometer works flawlessly, and does not jump in the slightest.

I'm going to try disconnecting the MAF in the morning and see if it changes how the car runs. If not, that would seem to be a likely culprit.

Hirnbeiss · #8 11-21-2014, 07:37 AM

With high Hc and CO, it's a mixture issue, so should be improved by the O2 sensor and MAF. The MAF inmy 124 gave up the ghost at about 130k miles.

oldtrucker · #9 11-21-2014, 12:13 PM

Quote:

I'm going to try disconnecting the MAF in the morning and see if it changes how the car runs. If not, that would seem to be a likely culprit.

If the car is running, it will die, after you disconnect...unless it is so far out of loop and doesn't give a hoot anymore.
If it is not running, it will probably not start or idle.
Be careful about the disconnect,there could be electrical spikes while disconnecting, reconnecting and in rare cases takes out the MAS, e.g. as Dom DeLouis would say "DED" dead...

Your Throttle Body wiring is OK? and I don't mean the outside sheath!
I might be getting to far ahead, so don't pay much attention to this question.

Codes from PIN 3 DTC is a different story.
They are perm codes, stored in a non volatile memory. There is a certain number of failures that have to occur before they get stored. Perhaps they are sitting in there for a while, but should have cleared, if they were fixed somewhere down the time line.
However, if I didn't grab the wrong table, then your codes match the description.
Makes no sense to me, though...
On the other hand, DTC doesn't give you all the codes, there maybe more within the HFM (pin 8) or cruise control / idle speed control (CC/ISC pin 14).

Have a look here http://www.peachparts.com/shopforum/3407971-post40.html post #40, pretty much the last one.
It is a very useful tool to troubleshoot OBD problems. Different control units have different codes and may give you more information.
So, it would not be a waste of time to built or buy one of them code reader.

As to the speed sensor, it could be a code from the ABS system. I haven't dug into that area very deep. Each wheel has a speed sensor that sends signals about the speed of a wheel to the ABS unit. I can imagine that, if one or more aren't working, it could cause a code via CAN bus to the DTC unit. In this case, your ABS would be in-effective or at least not working properly.
I have seen large amounts of metal shavings from the rotors, depositing on my front wheel sensors and cleaned them off, although I didn't have codes from there. These are magnetic (Hall Sensors) and if the deposit is thick enough might miss a few counts here and there.

NosserW124 · #10 11-22-2014, 11:45 AM

I probably should have mentioned that the ETA is already eliminated as a culprit - I had just replaced it with a date coded late production unit before taking the car in for the test. I too may have been getting ahead of myself, but at least I know that's not the issue now.

Parts arrive on monday. I decided to hold off on discoing the MAF in fears that it could hurt something else. Once I get everything installed I'll update the thread.

Thanks for all your help!

NosserW124 · #11 11-24-2014, 11:39 AM

Progress!

Parts arrived early on Saturday, so I dove in. Plugs and MAF are now in, and the difference in how the car runs is night and day - apparently this problem has been in play since I got the car, so without a point of comparison I thought it was running fine - it wasn't until now. Idle is now glass smooth, and throttle response is markedly improved. O2 will be going in tonight - then the BIG trick will be seeing whether or not the rich condition has killed the cat. I've only driven the car about 100 miles like this, (mostly picking it up from seller) so I'm keeping my fingers very tightly crossed that it won't need a new cat as well.

Any tips on "cleaning" or restoring a cat that has been hit with too much fuel?

oldsinner111 · #12 11-24-2014, 11:43 AM

I have also heard of running e85 to pass testing.Makes alot of sense,then fix your problem after that.

oldtrucker · #13 11-25-2014, 11:39 AM

Quote:

Plugs and MAF are now in, and the difference in how the car runs is night and day

Glad you are making progress.
It is tough to get a feel of how a 20 year old car should run without having an reference.

Once the CAT is gone e.g. there is nothing left of the precious metal inside, there is nothing that can be done other than replace it with either a new one (OE) or CARB approved after market for California.
But it may still be in good condition, if you don't hear any rattling coming from the exhaust.

Can't tell for sure until the pre-test with new O2 sensor has been done.

Quote:

I have also heard of running e85 to pass testing.Makes alot of sense,then fix your problem after that.

I tried, this so called "Sure Pass" without any results other than my wallet was lighter.
It might work, if the CO HC etc. is only a few numbers above pass threshold, but I had 4% CO and don't remember exactly the HC. Once I applied this and other stuff, it came out with 1% less than the test before.
Conclusion, I don't believe in it!
Alcohol might get you through but needs to be drained right away and after all the engine is still running out of wack...
In California, they may give you a one month extension to fix it or junk it. However, the registration fee is due no matter what, even if you decide to junk it.
It is also illegal to operate a Motor Vehicle without valid registration, therefore if your extension expires, you are not allowed to operate this vehicle on public roads, period. You may not get another extension.
This makes it even more complicated to complete your smog test, since you are not even allowed to drive to the smog station.

NosserW124 · #14 01-08-2015, 06:18 PM

UPDATE:

So finally got back over to the smog station after the holidays, and it passed! I squeeked under on HC at 25 mph (32 allowable, 32 measured) but as they say, a W is a W. I'll take it!

Thanks to everyone for your help - without it I'm pretty sure I would not have gotten to this point. Can't wait to finally get her back on the road.

liquiddog · #15 01-08-2015, 06:23 PM

D is for diploma! Congrats! Several "smog passed" threads going on lately. Means more survivor cars!