Failed CA Smog: NOx Too High

My high mileage daily driver failed badly. Almost double the NO allowed. Here are the gory details:

15mph @ 1520rpm: %CO2=14.40 %O2=0.47 HC=44 (max 110) CO=.01 (max 0.72) NO=1476 (max 772)

25mph @ 1152rpm: %CO2=14.37 %O2=0.57 HC=35 (max 85) CO=.01 (max 0.59) NO=1051 (max 711)

The service tech said it could be the egr, so I drove home and put a vacuum pump to the egr port. The engine stumbled as expected when vacuum was applied. That's about all I know to do to test the egr. I guess that doesn't prove that the electronic controller box is working.

I think it could be the cat. 220k on this stock one; way past its service life. Before I start throwing parts at the problem, I thought I'd check here first.

Besides the stuff in the signature, here are some other details: Scott Keller blue top smog chip, air filter and system returned to stock for test, stock (rebuilt) MAF used for the test, CA crap fuel plus some Heet and plus a little injector cleaner still left in the tank. I cleaned the top end with some Seafoam Green about a week ago and blew a lot of smoke out the tail pipe. New plugs and a fresh oil change before the test.

My O2 sensor is probably due for replacement, any effect on NOx?

charlief1: I would actually prefer to run a clean car, so I'll take your advice as a last resort.

Nick: Thanks, for your confidence in the rest of my car. I will replace the cat first. Any suggestions on where to buy a new one? I'll put it on myself.

x2 on the cat

Hi Ken, while a defective cat would not help with high NOX counts, I would really be interested in what your O2 sensor is reporting back, if contaminated it will be instructing computer to lean itself excessively causing a slight misfire, also the ignition timing might be a bit too much for low rpm operation(even though it helps throttle response).
Might get lucky to find someone local with accurate scanner to look at integrator(INT counts) and BLM's(block learn memory) for out of spec readings, 128 is count goals, high/low int is rich/lean corrective amount, BLM is long term adapting.
A simple fuel pressure adjustment may put you in good shape if O2 sensor is still good. good luck.

Kevin.

Make sure you have vacuum to the EGR off idle.

I'd try a gauge on the EGR vacuum hose while under load driving, and a voltmeter on the EGR line from the ECM to make sure the PWM voltage is there to pulse the thing.

Has that chip worked before in the past?

Just throwing in my two cents here but i would have to agree with nick on the converter statement. I have not had to make any tr pass emissions but my own. However i have had to make plenty of other automobiles pass e check and i have seen it many times before where a clogged or failed converter will affect nox. I mean think about it if its clogged doesnt it make sense that cylinder temps (nox) could possibly be higher then normal? Without having the car in front of me and assuming for the most part that the car is in decent running shape i would first look at the egr then would probably turn my attention to the cat. Like Nick said with that type of miles i would probably want to replace it any way. And as was said earlier i would also plug in a scantool and look at a couple other things such as o2 crosscounts or see if the car is runnuing incredibly lean Things of that nature. But from what i have seen fixing cars for the past 10 years (not saying thats a long time or that i no more then others) when i have a high nox situation i first look at egr then usually start looking at the converter (among a couple other things)

??? You are way off on the cat thing. I replaced hundreds or more at my old shop due to high NOX. More than EGR issues and other causes. We dyno pre OBD cars here.

a lean mixture will cause high NOx

Do yourself a favor and run down to the Napa next tor RPM muffler shop. Richard does pretty good work (off of north Melrose Dr.) Then put a few quarts of alky in the tank and call it good. I used the test site off of airport road near the little airport. He has discount coupons so you can test for cheap.

I used the alky in the tank and the car was way cleaner that it needed to be... (ie: like a new car)

Good Luck

Make sure the egr is getting a vacuum signal,i think you need a new cat it almost always fixed the high nox issue and the pre obd 2 cars.A lean mixture can cause high nox but when its that lean it usually developes a lean misfire and your hc's look fine.Get the cat and your done.

Got a new cat put in. I'll run half my full tank out to burn off the coating on the brick, then take it back for the test. Thanks for all the input, and I'll let you know the results later in the week.

which cat did you go with?

is it a honeycomb ceramic style, or is it the new spun metallic core style?

Walker 3" in-n-out. I supposed it's the old style.

pics ftw?

Failed Again



15mph @ 1566rpm: %CO2=14.40 %O2=0.34 HC=17 (max 110) CO=.01 (max 0.72) NO=1653 (max 772) [even WORSE than last time!]

25mph @ 1153rpm: %CO2=14.52 %O2=0.22 HC=13 (max 85) CO=.00 (max 0.59) NO=590 (max 711)

In California, cars this old must go to "Check Only" stations, which mean the service tech is forbidden to diagnose problems. Since I know the guy, he does try to help me, but he is certainly no expert on Turbo Regals. He still suspects that the egr system may be non-functional, even tho I tested the valve.

He also pointed out that I blew no CO at 25 mph and only .01 at 15 mph. He says "no way, there is always carbon monoxide." He said that low reading indicated perhaps a failed O2 sensor.

I should also point out that I noticed the typical d/s header crack when I did a top end engine clean in preparation for this test. I have another header already welded up and ready to install. Could this be sucking in air, throwing my O2 sensor off?