earthquake

90 Accord EX (F22A4). Failing emissions for NOx (NOx:2.61, 2.5 liimit). CO and HC are within range (CO:15.16, HC:0.78), however NOx is only slightly higher than allowed.

Would timing (advance/retard) change NOx, without impacting CO/HC?

Would a lower thermostat (170) lower NOx, again, without impacting CO/HC?

I have already replaced EGR Valve, O2 Sensor, Plugs, Filters, Oil, PCV. I have also used SeaFoam to remove carbon.

phootbag

If you open the EGR at idle does the car die?

earthquake

Yes, but to be certain that I didn't mis-read the diagnostics, I replaced the EGR anyway. I also cleaned out some carbon on that port and vacumed the port clean.

phootbag

NOx is created when Nitrogen burns in the combustion chamber. This happens around 2500 degrees F. EGR is the primary system used to reduce chamber temps and keeps NOx low.

Have you confirmed the EGR is opening on it's own?

earthquake

Again, yes. But to be certain, I replaced the EGR with a brand new EGR valve. I understand how NOx is created. My question is related to how I can reduce NOx without changing CO/HC. This car has been thru emission testing several times. Each time, all three values change. Sometimes good, sometimes not so much.

Would timing (advance/retard) change NOx, without impacting CO/HC?

Would a lower thermostat (170) lower NOx, again, without impacting CO/HC?

Here is what I remember about testing so far.

SORRY, I posted the wrong current values.
Trying to get the values online. Arizona stores the history online. Give me a minute to get them lined up with the repairs so far. That may help. Thanx for the help BTW.

chikin pickle

Ah, az emissions.
How old is your catalytic converter? If it's OE I would get the efficiency tested.

If you lower the temp of your thermostat. Your engine will run cooler and as a result, the ECU will add more fuel (lower the engine temp, the more fuel required). Your NOx will decrease,and your CO and HC more than likely will increase.

Other things to look for. If your exhaust manifold is cracked or leaking upstream of the o2 it will mess with the readings.

If your engine is running lean, NOx emissions will increase as well. (bunk O2s may cause this)

earthquake

This is a cronological list of what parts were replaced and the results of the tests.
12/24/2010
I changed oil and filters (oil and air), new PCV, new EGR gasket.

01/21/2011
Initial test failed on all three values. I was not able to obtain the exact readings.

02/12/2011
HC Result PASS
HC Grams/Mile 0.74 HC Std 1.00
CO Result PASS
CO Grams/Mile 10.70 CO Std 12.00
NOx Result FAIL
NOx Grams/Mile 2.53 NOx Std 2.50

02/12/2011
Replaced EGR Valve
Replaced spark plugs with NGK2262

02/12/2011
HC Result PASS
HC Grams/Mile 0.78 HC Std 1.00
CO Result FAIL
CO Grams/Mile 15.16 CO Std 12.00
NOx Result FAIL
NOx Grams/Mile 2.61 NOx Std 2.50

02/22/2011
Replaced O2 Sensor

03/03/2011
HC Result PASS
HC Grams/Mile 0.85 HC Std 1.00
CO Result PASS
CO Grams/Mile 10.65 CO Std 12.00
NOx Result FAIL
NOx Grams/Mile 3.02 NOx Std 2.50

The last graph of the test shows that the car is failing on acceleration.

earthquake

Just a little additional info. This car has had a very easy life. It was my moms car before we bought her a new one. I am giving it to my daughter. I know my mom wouldn't break a speed limit to save her own life. To say nothing of NO DIRT any where in the car. The interior is as clean as day one.

As a result of the easy life in Oklahoma where they have no emission testing, I am pretty certain carbon build up is possible and likely. I drove the car to AZ from OK and had no issues.

MAD_MIKE

You may want to pull the plugs on teh intake runners and clean those as well.
If they are clogged they will not allow the correct amount of exhaust gasses back in to the mixture to dilute.

Also note that your NOx is going up when you replaced the spark plugs and O2. NOx increases as the efficiency of combustion is improved.
Advanced timing will increase pressures inside the combustion chamber, as phootbag stated the high temperatures create NOx but also high pressure is needed. Make sure the base ignition timing is spot on.
Make sure those EGR ports are clear, if that is the case the cat may be in need of replacement.

MAD_MIKE

Yes carbon build up on the piston and cylinder head can increase the compression ratio slightly. I think its the EGR ports that need attending mild driving will allow the soot to build up in there. A few blasts on the onramp every now and then helps keep the egr ports clear. Cars with easy lives tend to have carbon built up in the EGR system.

http://home.comcast.net/~em-engineering/T2T013.pdf

earthquake

Mike and phootbag, thanx for the input.

I would like to be clear on what you have to say Mike. By the logic you are using, that advanced timing would increase pressure/temp and thereby increase NOx - would a retard in timing produce the opposite result?

Also, I'm not clear on what you mean by "pull the plugs on the intake runners". The only 'plugs' on the intake are injectors. I have not removed/cleaned the injectors. Is that what you are referring to?

MAD_MIKE

Yes, retarded timing would reduce the NOx emissions and actually cause the car to run cleaner. However,(always a catch) the car will be lazy and if part of the emissions check is to verify correct base timing, you will fail. But you can have the timing usually +/- 1* from factory specification and still pass. 3-5 or more degrees off and they will fail you. That was an old trick that folks used to do to get a car to pass emissions, prior to base timing checks.
My bad, I ninja edited my last post. Check out that pdf link in my previous post, it shows you how to remove the EGR plugs in the intake runners for clearing out the carbon build up.

earthquake

Thanx for the clarificatioin Mike. Base timing is not checked, so I may be able to get it to pass by cheating. I would prefer to 'fix it right'. I'm an aircraft mechanic and I beleive in fixing it correctly, however....this Honda has no wings. 'Lazy' is not such a bad thing with a new to driving teenager.

I'll look at your PDF and see what I can do tomorrow. It's dark now and I'm too old to be on the driveway under a trouble light (might scare the neighbors). and the testing station is closed until Monday.

Do you (or anyone reading) know of an inexpensive NOx/CO/HC sniffer/detector/sensor....?

earthquake

Not in CA. In AZ. Other questions already answered above, but thanx.

earthquake

Just an update to complete this issue. Turned out to be the Catalytic Converter. I found out that the life span is suppose to be 80,000 miles. At 240,000, and from all appearances, this is the original. It was almost an empty container. I am in the process of trying to replace it.

I would reccomend, if you have to purchase one - be certain they have the bolts and the gasket(s). The voice of experience. Now I am trying to locate the bolts and Honda wants $10 each - that is a $60 add on to the purchase of a new cat.

The bolt part numbers are 18176-P08-003 (x3) and 18176-PT0-003 (x3). The (x3) is three on each end.

I'll try to post after the emission test with results.

earthquake

FINALLY PASSED!!

It is amazing what a catalytic convertor will do. The cat is suppose to be on for 80K miles. This one was 240K. It was pretty much a hollow tube with some carbon debris inside. Hope this helps you. Be sure to read my previous post and caution on buying convertors.

03/17/2011
HC Result PASS
HC Grams/Mile 0.15 HC Std 1.00
CO Result PASS
CO Grams/Mile 2.30 CO Std 12.00
NOx Result PASS
NOx Grams/Mile 0.54 NOx Std 2.50