Smog Idiot: 1994 E420 Won't Pass With a 1992 400E ECU

[NCCoder]

So, it wasn't even until after I left the place that it occurred to me that I'd tried to smog my 1994 E420 with the 1992 ECU installed... Ugh... So, in addition to the EGR change over valve not receiving vacuum, and the "Check Engine Light" not illuminating, the CO was quite high, 9.45 at idle, and 10.18 at 2500. Idiot move, I totally understand.

One question is, will the CEL and EGR "issues" be taken care of with the installation of the correct ECU, or do I need to do some troubleshooting on the vac. hose?

Second question, does the O2 sensor have enough authority over the fuel to cause such a high CO reading by itself?

The car did pass smog in November, (long story about why it needs one now) so I'm surprised to find the gasses out of whack. Thank you all for your experience, and I do deserve any ridicule for the ECU stupidity...

 

[Jlaa]

My uneducated guess here —- I dont think the 1992 ECU caused your car to fail smog. Smog tests are never run on full throttle —- only part throttle —- and at part throttle the car is still relying on the o2 sensor to run as close to stoichiometric as possible. The richened-up fuel map only comes into play at wide open throttle.

Also just FYI - my 1993 500E passes NorCal smog tests just fine with a 1992 ECU.

 

[2phast]

Never had any issues with my 93 running the 92 ECU either.

 

[gerryvz]

I have used a 1992 LH computer for many years in my 1994 car. Had no problem passing smog tests in both Oregon and Texas.

You need to make sure that you drive the car at least 10-15 miles before you go in to get it tested, to ensure the catalytic converters are very hot and working as they should.

I once took a 1995 E320 wagon into a testing facility about 4-5 miles from my house, when I lived in Oregon. It failed the test. I drove it 10 miles the next weekend before bringing it back to the same facility, and it passed with flying colors. It's really important to make sure that the cats are working at peak efficiency before bringing the car to be tested.

Cheers,
Gerry

 

[gsxr]

Soooo... the 4.2L engines are a little different than the 5.0L.

In 1992, the 4.2L had a 10.0:1 compression ratio, while 1993-up had 11:1 compression ratio. I've also had some odd emission test results with a '92 400E LH module in a 93-95 400E/E420. Mostly the HC was higher than normal at both idle and 2500rpm. If the limits are tight/strict where you live, swap in the stock module, and drive the car for 5-10 minutes at 3000-4000rpm prior to arriving for the test to FULLY heat the cats (keep it in 1st or 2nd gear if necessary due to low speed limits). You don't need load, just high RPM. Really makes a huge difference.

The CEL is completely unrelated. If the bulb doesn't turn on when you turn the key on, replace the bulb. If there's a vacuum issue, you'll have to trace the plastic pipes between the engine and the 2 valves behind the passenger headlight, hidden behind the washer reservoir.

EGR not working *might* affect the emissions readings at 2500rpm, but I don't know for sure.

 

[northNH]

While you’re already thinking about this kind of 400/420 stuff...

What would you expect from swapping in a ‘92 EZL into a ‘94 that was already running well with a ‘92 ECU?
Anything worthwhile?

TIA

 

[gsxr]

Also - can you post the test results from both tests (November 2018, and August 2019), along with the limits of both HC and CO?

Forgot to mention, our 94-95 E420's always passed with a '92 module, but the readings were noticeably higher. Fortunately the limits are fairly high where we live so it hasn't been an issue. Something is different in the LH programming but I don't know what it is.

 

[gsxr]

While you’re already thinking about this kind of 400/420 stuff... What would you expect from swapping in a ‘92 EZL into a ‘94 that was already running well with a ‘92 ECU? Anything worthwhile?

@400Eric did this years ago, and found that a 1992 EZL (013- part number) installed in a 1993 400E (replacing an 014- part number) provided a pretty substantial improvement in performance, as measured at the dragstrip.

HOWEVER, the 4.2L EZL's are not all interchangeable like they are on the 5.0L engines, there is an engine number break, possibly related to the change between closed deck and open deck (not sure). Based on my experiments, I found certain combinations of EZL and LH part numbers don't work in a 4.2L with 11:1 compression ratio. That said, I think if both a 92 400E LH and EZL are used together, they MIGHT play nice together in a 94-95 E420... but I haven't driven a car with this setup yet.

 

[northNH]

As usual your response raises at least as many questions as it answers...

As my planned swapped-in 013-EZL is from the same ‘92 400 as the ‘94s current ECU, will there be an adaptation period while the ECU and EZL re-acquaint themselves before I know by the seat of my pants if the swap was beneficial?

Interesting, the EZL from the ‘92 still has its clear film nicely intact on the paste, which still looks reusable as is.
Film definitely there to minimize messiness.

 

[NCCoder]

I don't have the results for the November test, and I'm pretty sure this is the last time I'll be able to do the two speed idle test. From here on out, it'll be the roller.

As far as the ecu, I was hoping there was a difference in how the check engine light worked from 92 to 94, but it appears I'm wrong. What killed me was CO, 9.46 at idle and 10.18 at 2500. I'll have to figure out how to keep the cats at temp while waiting my turn at the station. Looks like I have some troubleshooting shared of me.

 

[gsxr]

WOW. Your HC is crazy high at 550-700. Something is definitely wrong here, a clean engine with *zero* catalysts shouldn't that high! This may be more than a simple ECU swap, but I can't tell yet from the limited info. The CO numbers are off the charts. You may need to Google and figure out what typically causes this. Perhaps your EGR valve is stuck partly open or something?

Heating the cats likely won't cure whatever you have going on here. I'd start by checking for other codes, but you may need live data to view the MAF airflow in kg/hr, and view the O2 sensor data, to get a better idea of what's happening. More questions - how old is your O2 sensor, and does the '92 LH module have a stock chip inside?

Also, you don't need to "keep the cats hot" for the test. Under normal circumstances, if you drive with the engine at ~3500rpm for 5-10 mins prior to arriving, even if you have to shut the engine off it shouldn't matter if they test within 15-20 mins (assuming it's not a cold winter day).

 

[NCCoder]

Oh, I'm fairly positive the o2 sensor is bad. My thought about the ecu causing problems was specifically the cel (as in 1992 did not have a cel but 1994 does which is why it doesn't light up at all) and operation of the egr (as in 1992 didn't even have egr and the 1994 does). The running rich is a definite problem separate from the ecu. Funny note about the egr is that he says the valve works but it's not getting vacuum from the ecu side, so it looks like your post about the lines behind the headlight is where I start. Thank you for your responses!

 

[gsxr]

I can explain about the CEL. The CEL is controlled by a separate box, the DM (Diagnostic Module). The DM monitors data from the engine computers and is kind of a watchdog, looking for anything that may affect emissions, and if it sees anything it doesn't like... it barks. Er, I mean it triggers the CEL.

You can remove the DM entirely and the car will run & drive without it; the DM/CEL was only used in North America. Although some (most?) 1992 USA model year 400E/500E's don't have the DM/CEL, the LH modules are totally separate and unaffected if the DM/CEL is present or not.

 

[gsxr]

As my planned swapped-in 013-EZL is from the same ‘92 400 as the ‘94s current ECU, will there be an adaptation period while the ECU and EZL re-acquaint themselves before I know by the seat of my pants if the swap was beneficial?

I think it will be a good test to swap in a 1992 400E LH+EZL into the 1994 E420, and see what happens. You'll know pretty quickly if anything is wrong, if you get weird codes stored, or an oscillating idle, or other weird behavior... that's not good. But if it remains code-free and drives ok, that's great. There should not be any significant adaptation required, just the usual bit where the '92 module adjusts to the 93-95 engine. The EZL has no adaptation capability.

Any benefits, if detectable via butt dyno, should be apparent right away. Eric's testing was showing, IIRC, a noticeable change through most of the powerband due to increased/advanced ignition timing. But I don't think he every dynod the two combos back to back (late EZL vs early EZL, in his 93 400E). Chronicles of his saga are on the forums from probably 8-10 years ago, possibly on PeachParts and/or BenzWorld, along with some postings on 500Eboard.

 

[northNH]

-Car is already happy with the adapted WOT ECU, the enrichment definitely works.
-EZL in the ‘94 is 015-; it was replaced years ago;
-will let you know what my butt says.

 

[gerryvz]

Also, you don't need to "keep the cats hot" for the test. Under normal circumstances, if you drive with the engine at ~3500rpm for 5-10 mins prior to arriving, even if you have to shut the engine off it shouldn't matter if they test within 15-20 mins (assuming it's not a cold winter day).

No matter if there are other elements causing the high readings (and I agree that O2 sensor is a primary issue, particularly if it's the original/stock one), getting your cats heated up is going to help optimize your test results whether everything else is perfect or not. Not saying it will (by itself) make your car pass, given you have other issues, but heating those cats will give you the very best results.

And yes, drive for 5 miles (freeway/higher speed) or 10 miles (mixed driving) to heat the cats properly. I agree that shutting the engine down for 15 minutes won't affect things as far as the cats' performance is concerned, as long as they are properly heated prior to shutdown.

 

[NCCoder]

I had driven it about 20 minutes @ around 75 mph beforehand, but it did sit for closer to 30 minutes before the test. I should have kept it idling... So, I guess I need to find out why the CEL doesn't light up, it appears most likely the bulb is actually burned out. I also need to verify the vacuum lines to the EGR valve. Thank you all! I'll try to keep this updated as I go. I hate it when we don't get to hear how it actually got fixed.

 

[gerryvz]

I bet you'll find that the bulb has been removed.

The CEL bulb is supposed to light up when you turn the key to position 1 (the "accessory" position) and before the position that starts the car. Or if you start the car it should turn on, and then off again after a few seconds.

If you don't see the CEL bulb light up at all, in any situation when turning the key, it's likely that it has been removed from the cluster, and at minimum is burned out (which is much less likely than it being removed).

 

[NCCoder]

I was really hoping not to pull the cluster.... ah well, it'll give me a chance to look at why my trip-o won't reset...

 

[gsxr]

I had driven it about 20 minutes @ around 75 mph beforehand...

To clarify - just driving the car doesn't help. It MUST have the RPM's higher than normal. 75mph is only 2300rpm. Next time, drive it in 3rd gear at 75mph which will be 3400rpm. Speed doesn't matter, if you can drive in 1st gear at 35mph that will be ~4000rpm and work just as well.

... but it did sit for closer to 30 minutes before the test. I should have kept it idling...

If it will sit for 30 mins, you don't necessarily need to keep it idling the whole time, but on a cool day you could re-start after 5-10 mins and let it idle a bit to keep engine temps & catalyst temps up.

The catalyst heating process isn't just to increase temperature, it also cleans the internal honeycomb by burning off contaminants. I've had to wait 15-20 mins (engine off) after arriving and still had very low readings.

Again, your HC numbers are so high, it isn't the catalysts... you must fix the main problem with the mixture.

BTW - how old are the spark plugs, and are they the correct non-resistor type? Have you pulled them for a reading?

 

[Jlaa]

I was really hoping not to pull the cluster.... ah well, it'll give me a chance to look at why my trip-o won't reset...

Don't worry, if you use the cluster extraction tools (which are cheap), it is very easy to pull the cluster. Trust me on this, if even *I* can pull the cluster, ANYONE can.

 

[NCCoder]

oh crap... cluster extraction tools? I've been a VW dealer tech, BMW tech at Dinan, a few other places, but I've never heard of extraction tools. I've got a lot of learning on this thing...
Haven't looked at the plugs, but at the moment, the car's running like a top except for slightly "stinky." Like I said, I'm pretty much going to install a new O2, and go from there. Have yet to read the codes to see what's there. Hopefully the cat's aren't too bad and they'll clean up.

 

[gerryvz]

oh crap... cluster extraction tools? I've been a VW dealer tech, BMW tech at Dinan, a few other places, but I've never heard of extraction tools. I've got a lot of learning on this thing...
Haven't looked at the plugs, but at the moment, the car's running like a top except for slightly "stinky." Like I said, I'm pretty much going to install a new O2, and go from there. Have yet to read the codes to see what's there. Hopefully the cat's aren't too bad and they'll clean up.

Two different examples:

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[NCCoder]

Sooo... Just tried to read codes, both key on and in accessory, held down for about 4 seconds, and no blinky. What am I doing wrong?

 

[gerryvz]

Sooo... Just tried to read codes, both key on and in accessory, held down for about 4 seconds, and no blinky. What am I doing wrong?

HOW-TO: Checking DTC's (Diagnostic Trouble Codes) on the 500E/E500 | "HOW-TO" Tutorial Articles

UPDATE: To buy a pre-built code reader, click here for an affordable one from eBay. If you do not have a "breakout box", make sure you select the type of reader with the small 1mm pins, i.e. for 400E, not the type with the large 4mm pins. A breakout box is highly recommended... this has numbered...

www.500eboard.co

 

[NCCoder]

So, now I get to diagnose the diagnostic module...

 

[gsxr]

Sometimes the DM will show zero blinks if there are no codes.

IIRC the factory spec is to hold the button for 2-4 seconds, I aim for 3. I don't know how it reacts if you hold it down for 5-6 seconds.

If the CEL bulb is good, but doesn't turn on when you turn on the ignition, the DM would be my next check (first to see if it's present and connected).

 

[NCCoder]

Yeah, looks like I'm going way back to basics here... on the DM, the light did come on when I pressed the button, but nothing after that. With what I know of the issues so far, I'd at least expect to see something about the o2 stored, probably the EGR and if my reading has been somewhat accurate, maybe a code for the secondary air system (vacuum lines swapped at the change over valves.)
Plan looks like getting the cluster out, see what that bulb is like then go from there. I found the plans for a blinker, so I'll make one of my own and go from there.

 

[northNH]

Result of EZL swap mentioned above:
Swapped a ‘92 400E EZL into a ‘94 E420 already running the LH module from the ‘92...

No incompatibility, car ran perfectly;
My butt could appreciate no performance benefit after 1 week of driving.
Maybe benefit with more octane than available 93?
‘94 EZL back in there.

 

[NCCoder]

Quick update: the bulb was there and good. Switching in the original ecu made no difference. Looks like the DM isn't connected somehow.

 

[NCCoder]

Thank you, Matt at Leistung for looking at my car. After running it out of fuel (broken fuel sender), I had it towed there to look at the other issues. Egr: smog tech was trying to scam me, dm: not 100% sure, seems like plugging in a test unit then plugging mine back in got it to work. Running insanely rich: looks like an air mass meter, not the O2.
Matt was very sympathetic and he got the car done, same day on a Friday. As a previous mechanic, I know what that means, and I am so appreciative.
So it looks like I'm in the market for a known good used\impossible to find reman unit.

 

[TerryA]

NCCoder,

Sorry for your troubles. You went to the right guy “Mat” for the fix.

Something you said back in post #10 caught my eye “From here on out, it will be the roller”

Due to the E500Es having traction control. In CA our cars have been exempt from the roller on the Smog Test.

Has there been a change in the CA Smog test? Have we lost the exemption from the roller?
That will present real problems passing smog in CA.

Have I missed something here?

 

[NCCoder]

I don't know if it makes a difference, but mine is actually an .034 I believe they're called here, an e420.
The smog guy did say there was something "special" with the transmission that prevented using the rollers, but then proceeded to run the car on the rollers "in order to test the egr system." Later failing me for faulty egr function.
This is my first experience with this car at a smog shop, and my previous experience was with another car from the same area (SF South Bay) that initially was idle only then after moving down here had to use the rollers. I will report back as I get more information.

 

[Jlaa]

If your car has factory installed traction control (ASR) then it is non-defeatable, and California exempts cars w/ non-defetable traction control from using the rollers.

https://www.bar.ca.gov/pdf/2017_Smog_Check_Manual.pdf

See page 10 -


Tailpipe Emissions Inspection

1.2.1 Acceleration Simulation Mode (ASM) Emission Inspection

Vehicle model-years 1976 - 1999 that are registered in the Enhanced Program area require an ASM inspection; excluding motorhomes and heavy-duty vehicles meeting certain conditions. See examples below.

The ASM emission inspection includes two loaded mode sequences known as the 50/15 test and the 25/25 test.
Inspectors must ensure that all the applicable before-test-conditions specified in section 1.2.0 are met before beginning the ASM inspection. Once the applicable before-test-conditions are met, follow the EIS prompts to conduct the ASM inspection.

CAUTION! Be aware that some vehicle designs are incompatible with a two wheel drive (2WD) dynamometer. Any attempt to operate such vehicles on a 2WD dynamometer could cause injury and/or may damage the vehicle. If the vehicle is not compatible with the ASM inspection then a TSI inspection shall be performed.

The following are examples of vehicle designs that are not compatible with the ASM test and therefore must receive the two-speed-idle test:

• Full-time all wheel or four wheel drive;
• Traction control that cannot be disabled;
• Body or chassis modifications made for business purposes that make the vehicle
incompatible with loaded mode testing;
• Unable to safely fit on the dynamometer;
• Motorhomes as classified by the Department of Motor Vehicles over 8,500 GVWR;
• Heavy duty vehicles with GVWR between 8,501 and 9,999 and with an unloaded drive
axle weight over 5,000 pounds.
• Heavy duty vehicles with GVWR over 9,999.

Notes:
For the purposes of a Smog Check inspection, the term “unloaded” shall mean that the vehicle is not currently transporting loads for delivery or is not carrying items of a temporary nature (bricks, sand, lumber, etc.). The GVWR includes items that have been welded, bolted or otherwise permanently affixed to the vehicle, and tools, supplies, parts, hardware, equipment or devices of a similar nature that are routinely carried in or on the vehicle in the performance of the work for which the vehicle is primarily used.
To ensure the appropriate test and emission standards are applied, always follow the EIS prompts.

 

[nocfn]

Local shop to me put a rwd bimmer on the dyno from that vintage, tore out his rear end, ended up paying damages and negligence to boot, plus a new machine for the shop owner. Wont Fup that agian - employee was canned and the shop almost went out of business.

 

[NCCoder]

I guess I have to make sure mine is not ASR equipped; pretty sure it's not.

 

[TerryA]

If the car is ASR equipped there will be a triangle in the middle of the speedometer.

You live in the OC take your car to the Penzoil Jiffy Lub at 4428 East Chapman Ave / Smog Test see Don Kile. He knows these Mercedes. If it’s possible to pass your car he can do it. OR Ask Matt Stockwell to recommend a SMOG Station he uses.

 

[NCCoder]

Definitely will, thank you for the tip! This guy that tried to "scam" me with the egr thing was on Lincoln just east of Orange-Olive. Expecting I'll not be going there again.

 

[NCCoder]

Just a quick update, very special thank you to @gsxr and Matt at Leistung. Gsxr set me up with a known good air mass meter and Matt calmly walked me through resetting the check engine light.
I'm realizing the air mass meter must have been bad since I've had the car as I felt it was "soggy" in low speed situations (leaving stop lights\stop and go traffic). As it must have been running at something like 10:1 AFR, that makes sense. It now feels much more like I expected my first V8 car would. Thank you all for the help and advice!

 

[NCCoder]

@TerryA , perfect call on taking it to Don. Patient and understanding, obviously very knowledgeable. Car is now 100% legit thanks to the help of all of you.

To recap: the ECU had nothing to do with it failing: smog tech error with checking the EGR caused the first "fail," a bad connection at the DM caused the second fail, and a bad air mass meter caused the actual emissions failure.

Matt at Leistung got the DM operating, GSXR provided the MAF, and Don actually knew what he was doing to verify the EGR operation. It truly takes a village! Now onward to find 17" wheels to fit the silver arrow front brakes!

 

[TerryA]

Happy to hear Don worked out for you. He has been doing my smog test for 20 or so years. Before my 500E he did my Euro 84 500SL. When it wouldn’t pass he would adjust the fuel distributor and get it to pass.

On to your next project.

Take Care

Merry Christmas!!

 

[slomofo]

Resurrecting this thread.

My 93 .034 has no visible check engine light on startup and the DM has no flash codes. I have also used a 38pin diagnostic connector with an AutoLogic diagnostic tool with no codes present. I pulled the cluster and replaced the bulb for good measure although it appears good.
Does anyone have any idea why this could be happening. I read that all .036's are CA Emissions compliant (when new) but I haven't seen info regarding that on the 400/420. The vehicle seems to run well but not as quick as my .036 but I chalk that up to the 50 ponies missing and the different gearing. I did a new upper harness not too long ago so I was wondering if something is not connected there.
TIA

 

[gsxr]

slomo, what are your exact symptoms / problems?

And yes, all USA-spec .034's are CA-compliant, same as the 036. The .034 feels much more "relaxed" due to the super-tall gears and less torque. You can swap the rear end to perk up the 034, it's a straightforward upgrade.

 

[slomofo]

gsxr -
no symptoms or problems. car runs spectacular. I just find it odd that the CEL doesn't illuminate on startup or with the key in the on position and the bulb is good.
If I keep this car long term, a 92 LH module and possibly some shorter gears (non-asr model) will be in order. Here's a pic for fun. She has depo headlamps now.

 

[gsxr]

OH - now I understand.

If the bulb is good, but the CEL doesn't illuminate with the key on / engine off, the DM itself may be faulty. You could swap DM's between your 034 and 036 to see if that makes any difference. It's located below the passenger footwell carpet and shield (single screw at the bottom).

Swapping in a 1992 LH module and 2.82 or 3.06 gears would transform the car. If it's non-ASR, there should be a number of 3.06 donors available. With ASR you're limited to 2.65 or 2.82 as the 3.06 with ASR is, as Gerry would say, rare as rocking horse poop.

 

[slomofo]

I'll inspect the DM under the footwell. That's a quick and easy peasy deal.
Yeah, if this one stays with me, rear diff and LH module will be a must. It's only got 106k on the clock so it's barely been driven and ready for the challenge.

 

[slomofo]

Thank you for the help

 

[gerryvz]

I have yet to find ANYONE who has experienced any real-world performance benefit/increase from putting a "WOT" LH unit into their car. This, in nearly 17 years of owning an E500.

 

[Jlaa]

gsxr -
no symptoms or problems. car runs spectacular. I just find it odd that the CEL doesn't illuminate on startup or with the key in the on position and the bulb is good.
If I keep this car long term, a 92 LH module and possibly some shorter gears (non-asr model) will be in order. Here's a pic for fun. She has depo headlamps now.

View attachment 93430

Lovely car. IMHO, whatever you do, please resist the temptation to put any more red on the car, like painting the bumper strips red. The black bumper strips are critical, visually speaking, to keeping aesthetic balance on the car. Painting bumper strips red makes it too red.

ALSO - to echo @gerryvz's observation - I put a 1992 LH ECU in my car and I didn't notice any difference. My butt is not very finely calibrated. I don't got WOT that often ... usually only once per drive.

 

[slomofo]

Lovely car. IMHO, whatever you do, please resist the temptation to put any more red on the car, like painting the bumper strips red. The black bumper strips are critical, visually speaking, to keeping aesthetic balance on the car. Painting bumper strips red makes it too red.

ALSO - to echo @gerryvz's observation - I put a 1992 LH ECU in my car and I didn't notice any difference. My butt is not very finely calibrated. I don't got WOT that often ... usually only once per drive.

From what I understand, the LH module from 92 is more of a benefit on the 4.2L cars.
I've since sold the car to another enthusiast to make room for a 95 E320 Cabrio.