High CA emission - bad cats?

[gearheademporium]

Greetings all, so I recently had my ignition dilemma remedied, which I now believed was due to condensation buildup in both distributor caps; however, in the process of troubleshooting this issue, plugs, wires, coils, caps and rotors, Cam and Crank sensors were replaced, which I thought could lead to failing smog a few months ago (High HC and just missed the mark on NOx).

Feeling confident, I took it in today for another go but this time had asked for a pre-test. The result was a disappointment. I'd like to seek some expert opinion here with the attached readings before I dive in to replace both cats and the O2 sensor.

As always, I'm thankful for the members' generous suggestion and guidance.

 

[gsxr]

High HC readings may be due to the catalytic converters. Are they factory or aftermarket cats? Do NOT replace factory cats unless you are absolutely, positively, 1000% certain they are bad. If the O2 sensor is of unknown age, I'd consider trying that first (and, resetting adaptation on the LH module afterwards). Does the LH module have an aftermarket chip in it? If you aren't sure, open it up and check. That could cause problems too. For years, some vendors were selling a chip for 400E that was actually a 5.0L fuel program.

Was your emission test at no load, or under load on dyno rollers (if your car does not have ASR)? Were the cats fully heated before the emission test? They must be HOT for the test. You can heat the catalysts prior to the test by driving at ~4000rpm for 5-10 minutes. You don't need high speed. On your 400E, 50-60mph in 2nd gear works fine. With the cats fully hot, test again.

However: Your HC numbers seem awfully high. I've seen a 500E emission test where the HC reading was <110ppm at 2500rpm with no catalyst installed (no load test / no rollers). If your car was on rollers under load that would be different. Something else may be going on with fuel delivery / mixture. On the bright side, you can rule out ignition problems.

It would be really helpful to find someone with SDS / HHT-Win so you can view the actual adaptation values on your LH module. If they are pegged at the limit, that indicates something is wrong with engine management, not the catalysts.

 

[gearheademporium]

Thanks for the reply, GSXR. The previous owner already had aftermarket cats when I acquired it in 2015, and I had to replace both cats and the O2 sensor 2 smog cycles ago. Actually, the HC reading did come down some after the distributor caps were replaced as compared to prior replacement but the NOx remains pretty much the same, and because the engine is running so smooth after all that ignition work, I thought perhaps it would make a difference so I took it down for a pretest; I've also reset the LH module using the battery disconnect method and logged some miles afterward. The pre-test was done on a Dyno at 15 mph. The current cats been on for several years and I wonder if the continued driving with the misfiring may have already damaged them. I've got a knockoff SDS C3 but the last time I've tried using it, it failed to locate the HHT app. Not sure if it was just a glitch but I'll hook it up and give it another go later this week.

 

[gsxr]

Ohhhh. If it already have aftermarket cats, they could have failed again. Aftermarket cats are far lower quality than the factory cats.

If the O2 sensor was replaced already, it should be fine.

Disconnecting the battery DOES NOT reset the LH module, at all. This will not clear codes and not reset adaptation either.

Not all SDS have HHT-Win available, but triple check to make sure. Also try navigating through DAS to select W124.034/.036, etc which should launch HHT-Win. You also need a fully populated 38-pin cable.

 

[emerydc8]

Feeling confident, I took it in today for another go but this time had asked for a pre-test. The result was a disappointment. I'd like to seek some expert opinion here with the attached readings before I dive in to replace both cats and the O2 sensor.

I have 100-cell aftermarket cats and if I don’t thoroughly heat-sink the engine/cats and run it at least 4000 RPM for a few miles prior to testing I usually fail. I also idle it in N at 3000 RPM for a minute or two just before driving it into the bay for testing. Then it passes with flying colors. It really is night-and-day between heated versus non-heated. Were things sufficiently heated up when it was tested? Do you have control of that in California or do you have to leave the car for them to test it? I usually time it so I’m there as soon as the state inspection station opens so there is minimal waiting time.

Are you using premium gas? Any additives like Marvel Mystery Oil? That could cause it to fail. Ask me how I know.

 

[TerryA]

@gearheademporium,
You mention your pretest was done on a dyno at 15 mph. Using the dyno roller may result in a smog test fail. If your car has ASR which you do mention in a previous post. The smog test in California [on 124 chassis with ASR] should NOT BE DONE ON ROLLERS!

Maybe you should try ANOTHER SMOG STATION. Make sure you drive the car on the freeway for about 10 miles at 70mph. To make sure the CATs are HOT run it in 3rd gear for a while to get the RPMs up to at least 4,000. Keep it hot until tested. You MIGHT JUST PASS.

 

[nocfn]

Or you can ship your car to Texas!

 

[gearheademporium]

Just wish to share I finally had the time this week to tinker on the 400e. Based on the dismal smog result I posted last month, I presume both cats were fried due to misfiring issues. A big shout out to all the folks on this forum who unselfishly had shared valuable info so I no longer have that misfire problem.

Anyhow, I installed 2 new aftermarket cats using pipe clamps, tightened down on the clamps best I could but still noted just a very tiny leak out of the joints. I thought that wouldn't matter much so I took my car to get a smog today. To my surprise, it failed due to high Nox reading between 550 to 850ppm. The technician told me he could hear a tiny bit of exhaust leak and I told him about where the tiny leaks were at. Right of the bat, he said the leak in front of the cats would definitely spike the Nox readings.

Long story short, I took it to a muffler shop nearby and had the joints welded, went back for another test and, lo and behold, Nox came down drastically and it passed! I'm thankful the tech really knew his stuff and of course, I did drive around a bit to ensure the cats were ready for the test.

 

[gsxr]

Thanks for the follow-up, and congrats on the successful smog test! I had no idea a small leak upstream of the cats would spike NOx reading.

Do you know how many miles were on the bad aftermarket cats, and what type / brand they were? I'm curious how long they lasted before causing a test failure.

 

[gearheademporium]

What I was told, since the leak was right behind the O2 sensor, it inadvertently had caused the sensor to think the mixture was too lean and so it compensated by enriching the fuel mixture, and subsequently spiked the NOx readings. I have been using the same type of cats made by Walker for years, and these were my second pair for at least 3 years and I think the misfiring did a number on them or else they may be okay. These cats are rated for 25k miles but since this is not my DD, the very first pair of cats I replaced lasted over 5 years.

 

[R129 UK]

What I was told, since the leak was right behind the O2 sensor, it inadvertently had caused the sensor to think the mixture was too lean and so it compensated by enriching the fuel mixture, and subsequently spiked the NOx readings.

This doesn't make sense to me assuming by behind you mean downstream unless you have post Cat O2 sensors fitted which I don't believe is the case...

 

[gearheademporium]

This doesn't make sense to me assuming by behind you mean downstream unless you have post Cat O2 sensors fitted which I don't believe is the case...

Like you, I was skeptical about what the tech said until I saw the end results with my own eyes after getting all the leaks weld repaired. It has only one O2 sensor and it sits upstream before the pipes split to go to both cats. I didn't mention how I had rigged up the 2 cats using muffler clamps; the cats came with 2.25" Inlet and Outlet so I utilized a reducer and an adapter (Bought at local O'Reilly auto parts nearby) and slipped them over the cats to mate to the OEM pipes, so perhaps there were actually more leaks aside from the most notable leak in front of cats that contributed to the high NOx, What matter most in this scenario was the car passed smog test legitimately.