2 part question

vairox wrote in news: snipped-for-privacy@4ax.com:

maybe a bad O2 sensor? any codes set on the ECU?

That's about the size of it - the NOx stage of the cat is bad... assuming it is a 3-stage cat. The absence of EGR makes me think that is so.

Make sure the timing is correct. Advanced timing will raise the NOx level, but AFAIK a 3-stage catalytic converter hides that as long as it is working.

Mike

thanks guys... the O2 sensor was replaced by a shop the last time it failed (in july 04) and it failed with harder NOX and a higher amount of HC, though it was still in the legal limit....

no ECU codes...

might install a magnaflow direct fit replacement, if i can get them to confirm it is california smog/noise legal...

sort of stumped cause i have another inspection coming up in june or july.... i am now using the proper OEM NGK plugs, did some intake cleaner throught the booster, idles much better, drives smoother... cleaned a lot of carbon off the pistons.

you guys know what effect a PCV catch can would have on emissions? i know it wouldnt do squat on NOX, thats temp related....but any others?

You're correct: A 93 Civic LX does not have an EGR system, according to my Chilton's.

This seems like a helpful site:

. See especially "Causes of Excess Emissions."

It puts a lot of emphasis on an improperly functioning EGR system causing high NOx , but it lists a few other causes, too. None are the PCV valve.

states similar.

An improperly functioning PCV valve may cause high CO, which you don't have.

What is a PCV valve "catch can"? Did you remove the PCV valve?

"vairox" wrote

thanks for checking the chiltons, i only have a haynes and it's not very specific about that... PCV catch can is just a can more or less, you take the hose that comes off the PCV valve and it connects to a can, then another hose goes from the other side of the can and goes back to where the PCV hose originally went, it just sits in-line of the PCV hose to catch all the oil blowby so it doesnt gum up the intake/valves etc... still allows the gasses to go by and get burned up...

what are the other causes of high nox? high combustion chamber temps due to carbon buildup is one but im not sure of any others

I can only guess: defective rings defective muffler defective cat. coverter valves not adjusted correctly timing set incorrectly defective plugs or plugs not gapped correctly

If you hook the engine up to a computerized engine tester--it should discover the source of the problem. I show a recent post where someone replaced all of the parts of his engine that might have caused his engine to stall on a regular basis. It makes more sense to use testing equipment to discover the exact cause of a problem instead of replacing a bunch of parts that are working great. Jason

Technically, the causes are high temperatures and rapid cooling, which causes the NOx to "freeze" instead of decaying as the gases cooled.

Since the expansion time is pretty much determined by engine speed, that leaves combustion temperature as the factor we can control. Carbon really isn't an issue directly, but it can cause preignition which has the same effect as advanced ignition timing. The two big culprits are ignition timing and mixture. Advanced timing increases combustion temperatures, and a leaner mixture at high throttle settings (when it should be rich anyway to forestall detonation) does the same. EGR reduces the temperature by diluting the mixture without affecting the air/fuel ratio.

Mike

good post. yes, check timing and mixture. mixture can be assisted by running a couple of tanks with injector cleaner through the vehicle. timing should be set with the maintenance jumper connected. and it should be dead-on, not just close. regarding egr, it's often addressed these days by increasing the overlap between exhaust and inlet valve timing, so make sure the valve clearances are correct.

to the op, no, an oil catch can is illegal in california.

why is a catch can illegal?

good advice guys, someone from another newsgroup claims that the car DOES use an EGR and said to go to

then put in part # EGV551

i can see a mount near the valve cover where one WOULD go, but i think the only cars of this era that had one are the ex and vx ?

may have to adjust the valves, it's pretty tough to get the timing dead on considering the rpm's go up when the fan kicks on to cool the engine, and finding 650rpm's EXACTLY on the tach is just a guess.

btw, rockauto.com is also coming up with the same product for the D15B7, and that mount area is on the backside of where the valve cover is, looks like where it would bolt on, only theres no opening into the engine there, or is there supposed to be?

because vapor still vents to atmosphere. you have to operate a closed crank case in ca.

that's a honda egr valve ok. but if you don't have one, you don't have one! they're only on the automatics.

two things:

1. unless the spec is changed for the 92-95, the d15 idles at 750 +/- 25 rpm. look up the procedure for adjusting idle correctly, then leave the engine management computer to do its job. /it/ controls idle speed - /you/ don't!

1. the timing set-up procedure requires the use of an electrical jumper which tells the ecu to keep ignition timing locked back. when you examine the timing under strobe with the jumper installed, the timing marks are very steady.* if the jumper is removed for normal operation, the marks jump about because the ecu is always electronically adjusting timing.

*. if the timing marks are /not/ steady with the jumper connected, re-tension the timing belt - it's not been set correctly.

theres a screw on the throttle body to adjust the idle, i've never messed with it so i should try again and get it as close to spec as possible then try again, 750 rpms is canada, 670 is usa

yeah i did the jumper, then started the car (was hot already)

they seem to be steady until the cooling fan kicks on then the rpm's get higher and the mark moves toward the back of the car

but i am usa. and that screw is not to adjust the idle. try it. it'll not make any difference once the iacv valve compensates. the screw is there to allow correct idle setup, and that's it. after that, it's the iacv all the way.

then something's wrong. the timing stays steady if the jumper is connected properly.