86 Maxima, 139K failing Mass emission, Nox. Here are the numbersHC gpm 1.35 (limit 2.0) PASSCO gpm 8.72 (limit 30) PASSNox gpm 3.85 (limit 3) --- FAILCo2 gpm 332.97 (limit N/A) NAAfter browsing through recommendations from this and other groups hereis whatI=E2=80=99ve done so far:1=2E Did a Lambda Calculation Lambda 0.9889; Air / Fuel Ratio 14.54This appears to be within acceptable range, and says that the mixtureis not to lean2=2E Basic EGR valve check:manually squized the diagraphragm which caused engine to chocke untilreleaseChecked the presence of vacuum on the hose going to the EGR valve(finger check)Checked the operation of EGR by revving the engine =E2=80=93 the diaphragmmoved up with higher RPM and back down when throttle was releases3=2E Checked O2 sensor by checking the self diagnostic codes on the ECU.Hanes manual says the lights should blink at least 5 times within 10sec at 2000 RPM in normal ECU mode. They do. I have not been able todetect any error codes in self diagnostic mode either, although I amnot 100% here I did it right. Also, I read somewhere that good air/fuelindicates that O2 is probably OK4=2E Visually checked Cat converter. It is present ;) and has no rust onit. It is a universal type, seems like an inexpensive type, not clearwhen it was replaced =E2=80=93 could be as long as 10 years ago, but the ca=rewas gently used.5=2E The thermostat: I did not replace it, seems like a lot of work onthis car. BUT the car does seem to run a bit hot(er), at leastperceptually and here is why: it has a shorted fan controls so the fansare always on, yet the temperature needle shows slightly above 50%scale most of the time even in 40 degree weather. There is also a bitof burning smell after the car has been on ran on a highway, but thatcould be due to some oil sipping on the manifold. The car DOES NOToverheat though. I also read on this forum that if you have a lambdaindicator, the engine temperature is adequate. Can=E2=80=99t say I understa=ndthis, but...

[snip]Can't guarantee this will fix it, but I had the same problem on aToyota 4Runner right before I sold it. New cat solved the problem (Ithad an el-cheapo cat on it as well) and it passed with flying colorsat 215k miles.

86 Maxima, failing NOx. Hereâ€™s what was done. What next?

Mar 15, 2006 26 Replies

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steve 20 years ago

To be sure you might retard the spark 5 degrees or so.

If nothing else fill up AGAIN before the test so you aren't blowing techron concentrate into the test machine! :-)

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steve 20 years ago

Pull vac on the EGR, if you get a strong responce at idle, it's working well enough to not be the problem.

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FNUJGSDLWDNP 20 years ago

Speak a little slower :) What do you mean? Pull the vac hose off the egr do what? I think I know what you mean, but want to be sure :)

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FNUJGSDLWDNP 20 years ago

Thanks Neil. I get it now. Based on Haynes manual, the diagram shows one large passage from EGR to

the intake. I have not figured out how to remove the EGR valave assmbly yet though to doulbe check -- the manual simply says "remove", so I must be missing something. I may swing by the dealership (I need to pick up some minor parts) and look at the print out diagram and then do the disassembly. Thanks for the tip!

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steve 20 years ago

Put manifold vac on the EGR valve at idle. If it makes a marked change (probably will stall), the valve and it's passages are OK.

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FNUJGSDLWDNP 20 years ago

I am curious, why are you against the Octane Booster. What are the other problems? Especially the one with MMT -- it is claimed to reduce NOx emission See the article

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I was thinking of using Prestone 0-60 with MMT booster. Like this one:

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If anything, can it hurt?

Max N

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steve 20 years ago

I'd be worried it might somehow show up as HC? Might work fine I've just never found the need for it.

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