DJP

Hello people,

I have a 92 civic si hatch with the following mods: short ram intake, stainless steel headers.

Since I've had the car, I've had to replace the following parts:

distributor, radiator ,oil pan, thermostat, fuel filter, spark plugs, spark plug wires, distributor cap and rotar.

I had recently went for my emissions test, and it failed giving rediculously high NOx reading (3300). One thing to keep in mind, is that this was after a cold start, but all other readings were well below the passing grade.

The first thing I did was purchase a new cat. assuming that since I was still using the orignal one that came with the car, it was about time that it had to be changed.

Prior to going in for a second attempt, I took the car for a highway blast and hit 7k rpm through each gear. The funny thing was, that the reading came back with even HIGHER NOx (3500), but all other readings were still WELL below the passing grade.

From what I have read, and based off the information I got from a couple of mechanics I know, high NOx is caused when the combustion chamber temperature is too high.

My question is, what would I have to do/change in order to drop the combustion chamber temperature?

fastrc2

EGR is how combustion temperature is controlled, and i believe your engine doesnt have EGR i am surprised theyy checked the NOX becuase i used to have a 91 crx si and i used to live in illinois and when i went through the pipe sniffer on the dyno the nox reading was tere, but the spec. for me to beat was dashes.

DJP

Is there an EGR quivalent on my car that would be responsible for that temperature control? I've also heard that this may be caused by the PCV valve, but that is a HEFTY replacement to fix...even if i were to purchase it aftermarket.

HondaPartsHero

you may want to change your O2 sensor if you haven't already and also check your ignition timing

thesmogman

What I think is happening is that your O2 sensor is taking a dump. I always suggest changing the O2 sensor when changing the cat.

If the O2 sensor is not oscillating correctly the cat will not get enough O2 to do what it is suppose to do. This is what I think is happening if everything else is in good condition.

Yes it could be alot of other things like your EGR is not working(If you have one)
fuel injector('s) mucked up, vacuum leak, carbon build-up, even an exhaust leak.

At 3500 something is really wrong to get that number with a new cat. Also I guess you didn't need a new cat!

EDIT: PCV valve expensive??? 15 bucks from honda. But usually a bad PCV either sticks open or closed. Open would let more air in thus leaning the a/f out. (Maybe your problem)Closed would raise HC and richen it up because the ECU believes it is opening and add's more fuel to compensate.

DJP

Yea..that was the most disappointing point...all that money down the drain...but as for the O2 sensor, wouldn't the CEL have at least come on..the only time i ever saw a CEL since i've owned the car was once during fall the yea after I had purchased it...the funny thing about that was..it only came on temporarily, and after i restarted the car it was gone.

The car has been running smooth ever since..so i'm not too sure....as for timing, I forgot to mention that I had changed the timing belt and water pump as well. After talking to my friend who actually did it for me, he showed me that it was SPOT on..one thing he was considering was retarting the timing a bit..but after lookin at the numbers, he also said that retarding it wouldn't help it enough in order for me to pass....

As for carbon build up, I've heard seafoam is pretty good, but I'm not sure what key areas to put it into to the engine so that it can work at it's best. Any recommendations?

thesmogman

O2 sensors can be stuck at a certain voltage and not throw a code. By your description of when the CEL did come on sounds like it was the O2 sensor. My 88 crx si did the same thing. Mostly during a long run up hill.

Your friend is correct retarding the timing is good for maybe 200-300ppm that is all. But if you were advanced say three degrees from spec and then set it to just below spec you might see 400ppm. or so.

DJP

Another thing I was wondering is whether or not this may be caused by the short ram intake? After speaking to both my friend (who is in an apprenticeship program), and my uncle who is also a mechanic, my uncle INSISTS that it has to go....i'm not sure why he is so sure about it...but with the all other readings being normal besides the NOx..i don't see why the intake would cause that....any thoughts?

DJP

bump

thesmogman

Short Ram is OK with a CARB number.

The reason he thinks that it would is because it is pulling in hot air from under the hood. It does make a difference, however a small one.

DJP

OOOOOOHHHHHHHHh...ok, that makes sense...but I had another question...with the short ram intake on, instead of a cold air, would I be actually robbing my car of gas milage...since the air used in the a/f mixture is actually warmer.. since a hot a/f mixture won't expand as much a colder a/f mixture?

IanB

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by DJP &raquo;</TD></TR><TR><TD CLASS="quote">OOOOOOHHHHHHHHh...ok, that makes sense...but I had another question...with the short ram intake on, instead of a cold air, would I be actually robbing my car of gas milage...since the air used in the a/f mixture is actually warmer.. since a hot a/f mixture won't expand as much a colder a/f mixture?</TD></TR></TABLE>

CAI uses more fuel than a SRI as the cold air is denser, and needs more fuel added to maintain the air fuel ratio that the O2 sensor is testing for.

thesmogman

That is what the IAC or the intake air temp sensor is for, to adjust the A/F ratio's for colder and hotter air. Also the stock air box draws air from both inside the hood and outside.

As for wasting fuel I didn't notice any change of mileage from the before and after on mine.