failed DEQ

[scott2]

I just failed DEQ. It seems odd as the guy just before me failed as well. Failed for high hydrocarbons and NOX. THC=5.5, pass=1.2. NOX=3.75, pass=3.0. I have not drove the car in a while, but drove it long enough to heat up the cats and had to idle for a while in line. I had just recently put on some DC headers and a 4.23R&P. I have RM exhaust and have the KN cone intake.

Anyone have some ideas.

I was running straight pipes for a while. Put the cats back on about a week ago and have drivin the car for a couple days. Does the computer need more time to relearn the cat configuration???

If the cat is too hot is that a problem??

I know many people are running this configuration or close to it.

Thanks,

 

[91BLACKANDBONENSX]

I had the same problem. My EGR valve was bad and replaced then no problems thru DEQ



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[lemansnsx]

Originally posted by 91BLACKANDBONENSX:
I had the same problem. My EGR valve was bad and replaced then no problems thru DEQ

High NOX is usually a pretty good indication of an EGR problem. Just curious: is your heat working well? Temperature gauge normal? Sometimes a failed thermostat plays into this.


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Andrew Henderson
The NSX Model List Page

"We have long acknowledged that enthusiasm for things automotive is a sure
sign of emotional instability if not outright dementia" - Brock Yates

 

[scott]

Temperature is good, right at the mid-point.

I will have a look into the EGR, I see a trend with the posts.

As a non-emmissions expert I would expect a closed loop system with an oxygen sensor to burn clean with low Total Hydro-Carbon output. My theory was that mabee a partially fouled plug may be causing inefficient combustion.

The EGR must recirculate alot of exhaust to reduce the THC by ~500%!

 

[NSXTC]

I remember hearing someone talking about a little trick you can do to dramatically lower your NOX by re-arranging one or more of the little vacuum hoses above the throttle body temporarilarly to pass emissions. Don't know which lines he was talking about, but said that was how he got his car to pass.

 

[lemansnsx]

Methanol is also supposed to be good for lowering NOX. There are some octane boosters out there that will give you the correct concentration - which I can't recall right now. Also, some of the emissions cleaner products like Guaranteed to Pass may do the same thing. The guarantee is crap - you'd have to jump through hoops to claim a refund - but the product has worked for me and others I have spoken with.
As for the EGR recycling a lot of exhaust - you wouldn't believe how much gunk and soot you will find in the EGR passages if it has not been functional for a while...

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Andrew Henderson
The NSX Model List Page

"We have long acknowledged that enthusiasm for things automotive is a sure
sign of emotional instability if not outright dementia" - Brock Yates

[This message has been edited by lemansnsx (edited 05 June 2002).]

 

[scott]

I looked up the EGR in the shop manual and it is supposed to recirculate exhaust gas and reduce NOX content. It would appear that it does not reduce THC?

 

[lemansnsx]

Originally posted by scott:
I looked up the EGR in the shop manual and it is supposed to recirculate exhaust gas and reduce NOX content. It would appear that it does not reduce THC?

THC? No, little or no effect from the EGR system. And I'll assume we're not talking about the "active ingredient" of marijuana which would normally affect only the loose nut behind the wheel.


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Andrew Henderson
The NSX Model List Page

"We have long acknowledged that enthusiasm for things automotive is a sure
sign of emotional instability if not outright dementia" - Brock Yates

 

[scott]

The guys at the DEQ thought they had a great deal snuffin THC all day long! To bad its actually total hydro carbon and not mary jane! They are too wacked to notice anyway.

The high level of THC indicates unburnt fuel. The catalytic converter is used to get rid of THC and NOX and CO. The EGR is suposed to get rid of NOX. Now there is also evaporative emmisions control. This would be the charcoal canister, vapor purge control system, fuel tank vapor control system. When the pressure in the fuel tank gets high the pressure is bled into the charcoal canister. I doubt the evaporative system would have enough volume to cause a DEQ faiklure although it would put unburnt HC in the system. I am suspecting the cats.

As far as the vacume hose switching thing....I wonder if this method is to hook up the EGR to a constant vacume source so it is on all the time??? I'll have to read the service manual some more

 

[lemansnsx]

Originally posted by scott:
The high level of THC indicates unburnt fuel. The catalytic converter is used to get rid of THC and NOX and CO.

Yes, it does indicate unburned fuel possibly indicating that the mixture is off. The catalytic converter, however, is only the last link in the chain. There are other things upstream that you should look at before blaming the catalytic converter. IOW, do not change the cat until you have eliminated everything else because the cat by itself will NOT clean up the problem.


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Andrew Henderson
The NSX Model List Page

"We have long acknowledged that enthusiasm for things automotive is a sure
sign of emotional instability if not outright dementia" - Brock Yates

 

[nsxman]

Check your ECU for failure codes.

 

[scott]

I replaced EGR and made sure the cats where heated way way up and threw in a bottle of STP gas cleaner. I now pass NOX at 1.49 and 3.0 limit. However, fail total hydrocarbons. THC are reduced to 2.81, limit=1.2. So this is down quite a bit from previous test.

I do not know how much is actually from the EGR. My old EGR looked good. I sucked on the vacume port and the valve opened no problem. There was some carbon buildup inside the EGR. I wonder if I need to clean carbon from the lines that go to the EGR?

When I first start the car I do smell some un-burnt fuel in the engine compartment? It is not real strong but noticable. I will chech vacume lines etc.

There are no error codes. The car runs strong.

Would O2 sensors fail without a squawk code??

Any ideas??

I am going to check vacume lines and fittings as I just had the car serviced and the tech may have forgot somthing.

What is the best stuff to use in the gas to pass?

 

[hendu]

Originally posted by scott:

When I first start the car I do smell some un-burnt fuel in the engine compartment? It is not real strong but noticable.

Any ideas??

Possibly a leaky injector, is your car ever hard to start after you just turned it off, i.e. a warm start. Just an idea.

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1994 Red/Black NSX #418
Forums Nazi Groupie

 

[hk4site]

Run at least 25% alky that should solve the problem