Help: Failed NOx test in MA 1990 300SE

Good Old MA dyno testing gets me

Grams Per Mile
Reading Limit
HC 1.06 2.00
CO 5.86 30.00
NOx 4.17 3.00
CO2 359.26 N/A

Car Details:
1990 300SE 228,000 Miles
Car was running hot little over 100C
Only had mid grad gas in it 89 octane
Car sat idling for 5-10 mins before being tested

Cap, rotor, plugs, wire, filter, EGR valve replace less than 30,000 miles ago
Cat. was replaced back in 96 or so at 70,000 miles

Does the car need a new cat. system?

Or should I retest using premium gas and when it is running cooler and not allowed to idle so long before the test?

I have one more shot before I have to pay another 29 bucks.

Thanks
Dan

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1969 RS/SS Camaro Conv. L-89 Alum. Head 396 375HP 4-spd

1987 GNX #419, 2002 RX300

FS: 1934 Ford Street Rod, Blown 383 $48,500 Firm

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HC and CO indicate that the catalyst is probably okay. If there was any detonation during the test, this could increase NOx, so I recommend premium for the retest, but make sure the engine is hot as was the case with this test. The engine and cat need to be hot to keep HC below the ragged edge.

Since NOx is the only real issue you should thoroughly check the EGR valve control system to be sure it's functioning properly.

Duke

Also go out and get yourself some of that "Liquid Inspection". Its some sort of octane boosting concoction. If you tell the guy at the parts store that you need some of that stuff that you pour in your tank that's supposed to aid in passing the inspection test ...they should know what you mean. If one doesn't go to another. Get an experienced guy, not some kid. I can get it here in TX at Autozone and O'Reily's Auto parts chains

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Regards,

Albert
aldedmon@yahoo.com

Just me...

But I've always put an airfilter, added techron and then changed the oil prior to testing.

My 86' is running extremely high on NOX- but I believe an 86 doesn't have an egr valve. Any suggestionsz?


For your answer- I think I'd try running preimum which is what the factory suggests.


Michael

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Michael McGuire
83 300d
01 vw A4 TDI
66 Chevy Corsa
68 GMC V6 w/oD
86 300E

The cat was repalced in 96 with 70k and you now have 228k looks like the replacement did its job.

How much oil do you use? An old cat burning oil will need to be run at better than idle speed to keep the cat lit off. if the replacement cat wasn't a MB cat I doubt it is doing anything now.

We have never had testing in our area so I don't know test procedures but the car should be warmed on the dyno for a brief period before the test is run. If you are in the car while it is waiting I would hold the idle to 1500-2000 for a minute just prior to testing.

There was some testing done in Florida but it was just idle testing. There was a dyno at every station though. its use was to precondition the cat by driving under load for a brief time.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

An O2 sensor that's lazy will raise both the HC and NOx.

The mixture going to the catalyst has to be just right.

$29.00? Man, you're lucky -- Here in California, I paid $80.00 (failed) then another $60.00 for a re-test (passed). Was told to add Techron, drive on the freeway for 40 - 60 miles and bring it right back. Passed on that second go-'round. Good luck!

Brian

That's how the screwballs from C.A.R.B can afford $ 150.00 lunches.

Ask me how I know.

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2007 C 230 Sport.

manny:

You must have been a CARB official in your former life, and now are under the witness protection program there in Canada

Brian

Ha, ha. No. I used to attend workshops with these radical screwballs.

I could never lower my ethical standards enough, to work for an outfit like C.A.R.B.

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2007 C 230 Sport.