Car Smog Fail Help: High NO

[RS250 Chester]

1990 Nissan 240sx just failed smog due to high NO. Car has 150K miles.

Smog report:
15mph Test: HC 18 (max 85); CO 0.11 (max .54) NO 984 (max 565)
25mph test: HC 13 (Max 67); CO 0.08 (max .45); NO 943 (max 522)

From what I've read, it seems that my CAT is ok, but my EGR maybe at fault, running to lean or an air leak.

Plugs and wires are fairly new, air filter ok, fresh oil and timing is spot on. But I am experiencing some knocking. Running too lean maybe?

Any ideas.

 

[tommygunracer]

vacuum hoses are cheap replace them so is the EGR . Take carb cleaner and spray around intake manifold gasket to make sure it doesn't leak , the engine will change rpm if it does.

 

[Diezel]

vacuum hoses are cheap replace them so is the EGR . Take carb cleaner and spray around intake manifold gasket to make sure it doesn't leak , the engine will change rpm if it does.

High NOx alone doesn't indicate a vacuum leak, usually. However the imports of that year were well known to have EGR problems.

I DO agree with replacing the vacuum lines, and cleaning the EGR.

OP can you give us all the numbers please? I'd like to see CO2 and O2 plz.


Now are we talking Knocking, or a Spark Knock (sounds like bb's in the engine)...

 

[RS250 Chester]

High NOx alone doesn't indicate a vacuum leak, usually. However the imports of that year were well known to have EGR problems.

I DO agree with replacing the vacuum lines, and cleaning the EGR.

OP can you give us all the numbers please? I'd like to see CO2 and O2 plz.

Now are we talking Knocking, or a Spark Knock (sounds like bb's in the engine)...

Complete Reading as follows:
15mph Test: %CO2: 14.9; %O2: 0.2; HC 18 (max 85); CO 0.11 (max .54) NO 984 (max 565)

25mph Test: %CO2: 14.9; %O2: 0.1; HC 13 (Max 67); CO 0.08 (max .45); NO 943 (max 522)

As for the knock/ping, its only on acceleration, like the octane isn't high enough or its too lean. It's not the timing chain guides or valve noise that are typically for the this car.

I did check the ECU, no codes, comes up clear. The EGR is the original and is a pain to get to. It does seem like the car is running hot, but the temperature gauges are reading normal.

 

[YOUNGTHRILL]

Sounds like your cat isnt doing whats its designed to do.....high indicator of nox points to the cat......also check your all the valves with vacum lines...you can do this with a simple vacum guage...if it doesnt hold presure there faulty....good look.....run good gas and make sure its at operating temp when u to take it back......if all is well and your only failing buy lets say 100ppm on nox fill a full tank of gas and add 1 gl only of deseal...sounds funny but its been provin and tested..........

 

[essvee]

This tip might work for you, it has worked for me on two vehicles that had similar issues.

Find a shop that's not super busy (so you won't have to wait long). Get your cat(s) HOT. Drive several miles on the freeway in a lower gear than normal. The object is to run the motor at a steady, moderately high RPM. Please don't blow your motor and watch the temps. Again, do this for a few miles.

Pull in to your smog test location and LEAVE THE MOTOR RUNNING. The object is to bring those cat's in as hot as practical.

Works like a charm for me but YMMV.

OP didn't indicate what part of the bay. There is an HONEST test only station in Los Gatos that has helped me pass (strictly legally!) that did my retests for free after telling me the above method. Right off Hwy 17. PM if you want the station.

 

[R1PLAYA]

check the EGR this is notorious for getting clogged up if your cat was at fault your numbers for CO would be high as well.

even tho its a pain to get to take the time to take it off get a can of carb cleaner and spray into valve and port (hole in engine/ manifold) get you one of those battery cleaner wire brushes if you cant find the one on a cable with a handle ( this is best) and after you have soaked the crap out of the valve and the port let them sit for at least 5 mins and then GET THE SCRUBBIN i mean go to work on that thing especially the port if you are not gonna replace the EGR.

check your vacum lines with the carb cleaner as well listen to the idle it will rise slightly if theres a leak and you can usually hear it . but if not get you a super secret vacuum leak finding tool dont worry snap on or mac dont carry it so its fairly cheap . go to kragen and by at least 2 ft of water hose like a mini radiator hose . hook one side to your trusty ear and scan the engine vac hoses with the other if you hear a hissing sound there is your leak

also if you havent changed the thermostat and flushed the coolant now would be a good time as NOX emmisions rise with temp.

 

[mototireguy]

+1 for running the test with the engine as hot as possible. Catalytic converters do their best when hot.

If that doesn't work and other possibilities have been excluded then it's possible the catalytic converter has given up. Cats do wear out and perform poorly after enough miles/time have passed.

 

[Motech]

Pinging + high NOx = non-op EGR, plus maybe advanced ignition timing.

Those cars are known for EGR hose coming dislodged from charcoal canister, left front of engine compartment near air cleaner housing, #s 7 & 8 in diagram. Both EGR and canister get signal from same source, when off the canister, signal lost at valve too.

Also check silicone hose connects from exhaust port on EGR valve to bottom of EGR backperssure transducer, #21 in diagram.

 

[RS250 Chester]

Pinging + high NOx = non-op EGR, plus maybe advanced ignition timing.

Those cars are known for EGR hose coming dislodged from charcoal canister, left front of engine compartment near air cleaner housing, #s 7 & 8 in diagram. Both EGR and canister get signal from same source, when off the canister, signal lost at valve too.

Also check silicone hose connects from exhaust port on EGR valve to bottom of EGR backperssure transducer, #21 in diagram.

That's awesome info.

I just moved back to the Bay after 6 years in San Luis Obispo County, the laws there weren't as strict and didn't require a dyno test. The last time I smogged in the Bay was 2005, it failed that time due to advanced timing. They moved it back to 15 and I swear it ran like crap once they did that. My mpg went down, pinging started happening, but the car then went to my daughter and she just kind of lived with it I guess, didn't know any better. My EGR might have been clogged then. Since we had moved to Pismo, smog tests were never an issue.

I'll see what I can do to get to that EGR, its below the intake, next to the firewall. It's going to be a PITA.

 

[KC@ BRG Racing]

from your numbers looks like the car is running pretty good. Hi nox is an indication of hi combustion chamber temps. U may have a thick layer of carbon on the piston and the head chamber. give you a higher then normal compression. Your nox numbers very hi. i think u may be over loaded the cat.
how does the car run? whats a compression test say.

 

[busapassion]

Pull the egr off and clean it out of all the soot and everything.

 

[Motech]

Those numbers are incomplete. Without CO2 and O2 readings, no way to tell how precise fuel control is.

Compression test a waste of time. If there was a compression issue, HC would be through the roof.

A competent emissions tech could nail this problem in less than an hour, maybe fix it too. I'm guessing this diagnosis and repair would fall between $100.00 & $200.00.

If you'd like it nailed way cheaper and don't mind a drive to Santa Cruz, send me a PM.

 

[Thateguhate]

Run that guaranteed to pass. Its like $15 or $20 for a bottle but it works. Temporary fix for you're problem though unfortunately. It will just get you to pass..

 

[Diezel]

Sounds like your cat isnt doing whats its designed to do.....high indicator of nox points to the cat......

Uhm. NO, plain out NO. When you have a single gas failure, that is usually NOT the cat as the root cause. Unless the cat has a seperate bed for NOx reduction that has basically disintegrated and disappeared.

check the EGR this is notorious for getting clogged up if your cat was at fault your numbers for CO would be high as well.

+1

Pinging + high NOx = non-op EGR, plus maybe advanced ignition timing.

+1

from your numbers looks like the car is running pretty good. Hi nox is an indication of hi combustion chamber temps. U may have a thick layer of carbon on the piston and the head chamber. give you a higher then normal compression. Your nox numbers very hi. i think u may be over loaded the cat.
how does the car run? whats a compression test say.

Very Possible. But knowing the years and those imports well. I would say if the car doesnt burn oil through the cylinders, It is less likely to be carbon buildup. Then it would be a plugged up EGR system.

Those numbers are incomplete. Without CO2 and O2 readings, no way to tell how precise fuel control is.
If you'd like it nailed way cheaper and don't mind a drive to Santa Cruz, send me a PM.

Hence why I asked about them too. The CO2 and O2 readings give a good indication of how well the fuel control system works.

Run that guaranteed to pass. Its like $15 or $20 for a bottle but it works. Temporary fix for you're problem though unfortunately. It will just get you to pass..

Right.....

 

[KC@ BRG Racing]

Complete Reading as follows:
15mph Test: %CO2: 14.9; %O2: 0.2; HC 18 (max 85); CO 0.11 (max .54) NO 984 (max 565)

25mph Test: %CO2: 14.9; %O2: 0.1; HC 13 (Max 67); CO 0.08 (max .45); NO 943 (max 522)

As for the knock/ping, its only on acceleration, like the octane isn't high enough or its too lean. It's not the timing chain guides or valve noise that are typically for the this car.

I did check the ECU, no codes, comes up clear. The EGR is the original and is a pain to get to. It does seem like the car is running hot, but the temperature gauges are reading normal.

I'm sorry i thought CO2 O2 HC and CO where the 4 gases we are working with here. or did i miss something here.... and from what i see you cars runs pretty good. Have you checked the timing. if it is where it should be, then i'd still say your compression is higher then it came when the combustion. chamber was new and clean. If it is carbon build up There are many way to cleaning it out.

Those numbers are incomplete. Without CO2 and O2 readings, no way to tell how precise fuel control is.

Compression test a waste of time. If there was a compression issue, HC would be through the roof.

If you'd like it nailed way cheaper and don't mind a drive to Santa Cruz, send me a PM.

Why would a compression test be a wast of time. if nothing else it would either confirm. My dio or at least take it off the table.

Why would the HC numbers be through the roof.

Are those the numbers your looking for? when you say compression issue do u mean to high or to low.

Also do you know why car engines have a EGR valves.

 

[Motech]

Why would a compression test be a wast of time. if nothing else it would either confirm. My dio or at least take it off the table.

Why would the HC numbers be through the roof.

Are those the numbers your looking for? when you say compression issue do u mean to high or to low.

I mean low, which would create misfiring, which would elevate hydrocarbon levels above what his were measured. I do not believe carbon build-up could raise compression so much that that alone would cause his sky-high NOx levels, especially if EGR flow and catalyst were present and ignition timing within specs.

Also do you know why car engines have a EGR valves.

Yes, I have a fair idea: To reduce NOx emissions, nothing more. It is accomplished by introducing inert exhaust gases into the combustion chamber under moderate loads that serve to reduce combustion temps. It is very effective when EGR flow is present. Remove EGR flow, temps go up, pinging can occur and NOx emissions rise dramatically.

 

[Motech]

I'm sorry i thought CO2 O2 HC and CO where the 4 gases we are working with here. or did i miss something here.... and from what i see you cars runs pretty good. Have you checked the timing. if it is where it should be, then i'd still say your compression is higher then it came when the combustion. chamber was new and clean. If it is carbon build up There are many way to cleaning it out.

My bad, I did not see that post, just the first one where he did not include CO2 and O2 measurements. Yeah, by those numbers, his fuel control is flawless. EGR is the likely culprit, maybe catalyst if EGR doesn't fix it.

 

[Motech]

BTW, compression testing is a waste of time 90% of the time, and with OPs emissions numbers, a 100% waste of time. There's no way he has compression loss with those stellar numbers.

Leakdown testing is also a gross waste of time until compression losses are around 50%.

 

[RS250 Chester]

So I started snooping around to see what is involved in removing the EGR, pain in the ass, I'll give it a shot and if its too much of a pain, I'll send it to someone.

I did find a loose bolt on the exhaust manifold that was causing a leak. This explains the little drops of oil I was coming off the clutch assembly. Did that contribute to the high NOx too?

Motech, I'll send you a PM in a bit.

Thanks everyone for their help, very informative.