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91 Accord fail CA emission test (NOX too high)

01-13-2011, 02:17 AM
Just bought this car. Its a 91 Accord with 250,000 miles. When car warms up, it has the idle fluctuation in park. Doesnt do it when it is cold. Think its the IAC valve. Took it for the great California smog check today and didnt pass on the NO (nitrogen) part. Everything else passed, the Co2, o2, HC, and Co passed fine. The NOX level at 15mph was 1437. The NOX level at 25mph was 1232. The CA max level is 559 (15mph) and 516 (25mph). The mechanic said its the EGR valve or the Cat Converter!! After I got the car home, the car was idling and I compressed the diaphram of the EGR valve, the engine stumbled.......... The car also has this annoying sounding aftermarket exhaust on it!! Any advise is more than welcome. Thanks

01-14-2011, 11:42 AM
EGR valve did pass your test but the passages in the engine might be clogged. That could be one of the problems. Another one would be the aftermarket exhaust. They do not last long, but it is practically impossible to find OEM for this year's Honda.


01-16-2011, 07:08 PM
How did you compress the EGR valve? Generally activating the EGR valve, checks the exhaust ports that directs exhausts gas into the intake manifold. The positive test that the engine is stumbling means the ports are probably clear. But do you know if the EGR valve is activating with engine vaccum when it is supposed to. Is the computer tellng the valve to open and is the solenoid opening and engine vaccum getting to the EGR? Are the hoses connected correctly and not lcracked/leaking? Many questions. Honda has a test for the EGR valve. and for checking the ports. The cat converter could be the problem but due to the cost, check everything else before going the Cat route.

01-17-2011, 01:32 AM
Thanks somick and mpumas for taking the time to reply. Today I took the EGR off, replaced the gasket, and cleaned it. There wasnt a build up of carbon on the ports. Used Carb cleaner on every hose and gasket on the engine and didnt notice a change in the idle. Soo now I am ruling out a vacuum leak. As you said mpumas, I dont know if the solenoid is responding properly to the vacuum. Is there a way to check that?

Another thing I noticed today was while driving on the freeway about 60mph. The engine was just slightly surging a bit. Not much at all, just enough to see the tach move a little.

I plan on changing the "annoying sounding" aftermarket exhaust anyways but, if it was bad, would that be causing the excess in NOX for the emmision test?

01-17-2011, 02:31 AM
I just thought about this, can a bad idle control valve (IAC) cause the engine to run too lean or rich which causes high NOX readings??

01-17-2011, 06:35 PM
You said it should have killed it if it was idling and you fully compressed it.

Did you try running a wire through the EGR to exhaust pipe and make sure it wasn't restricted farther down?

Possible the valve is working, but not getting enough flow through a neck-down in the pipe?

01-20-2011, 02:27 AM
This car is driving me crazy!! i did the compression test again on the EGR and same results. Stumbled but did not stall. Ran a long zip tie in the EGR exhaust ports with no restrictions. EGR has suction when engine is reved.

Had the resonater replaced but not the muffler due to cash flow right now. Resonater was the cause of the "annoying sound" anyway. Mechanic at muffler/smog shop said the muffler was bad too but would not hinder a emissions test... Is he right??

Exhaust fumes smelled like gas soo I adjusted timing by hand. Idling went from 1000 rpms to about 700. No smell of gas in exhaust fumes now..

Added a "decarbonizing" liquid to fuel and drove it hard for about 20 minutes. Ran good and strong. Next day while driving it, CEL came on and engine would lose power and sputter at 3500 rpms!! This would happen as soon as I stepped on it and the engine would reach 3500 rpms. Wondering if some carbon broke loose and is clogging something somewhere????????


01-21-2011, 01:55 AM
The Honda test for the EGR is to disconnect the vacuum hose and connect a vacuum pump to the EGR and pull 8" vacuum to open the EGR. Clamp off the hose and ensure that the valve stays open and holds the 8 " vacuum. (This test is important because if the diaphram leaks, it won't open enough to let the exhaust gas by to reduce the NOX.) Let the EGR relax. Start the engine and at idle pull 8" vacuum on the EGR. The engine should shudder then stall. If it doesn't you may/probably have plugged ports (one for each cylinder) at the intake manifold. This is a common reason why you fail the NOX on the smog test. The fix is not hard but takes drilling out/pulling out the plugs on the intake maniford, drilling out the ports under the plugs you removed then replugging the holes. You can buy replacement plugs from Honda. Bad mufflers and resonators do not cause high NOX, but a bad Cat converter will. So will a vacuum leak because it causes the engine to run fast on idle and lean and too hot creating high NOX at around 15-25 MPH. (That is range that the EGR opens throwing exhaust gas into the cylinders.) Timing is controlled by the computer so it should be set according to specifications and then let the computer do its thing. After decarbonizing you said the CEL came on. What code came up that caused the light to come on?

01-24-2011, 02:53 AM
Today my new IAC and FIT valves came in. FINALLY!! Anyways, I installed them and they seemed to fix the fluctuating idling. Drove the car around the block then let it sit and idle for 20 minutes. Fans kicked on and I reved engine, never did the idle fluctuate like it did before!!! Happy to solve that problem. Still dealing with the stuttering at cold idle and stuttering/total loss of power at 3500 rpms. This car NEVER did that until I messed with the timing by ear and rpms, flooded the fuel tank with octane booster and a decarbonizing liquid, and changed the EGR valve with another "used" EGR valve......... One of these three is the culprit I believe. Just dont know which one.

01-25-2011, 11:33 AM
If it's flattening out, sputtering and refusing to rev at 3500, this is the PCM going into "safe mode", where it drops the rev limiter to a lower level because it is sensing erratic/abnormal timing or no timing signal. That's the magic rpm number for when this happens.

I think you just retarded the timing too much, or the cam position sensor in the diz went bad when you moved it, wire pulled, something...

01-26-2011, 12:30 AM
I got TOTALLY fed up with this car today!! Took in to a recommended shop. Paid 90 bucks. Got it back and it purrrrred like a kitten and ran like a bat out of hell. No CEL, no stuttering/stalling. You were right Jeff. The timing was retarded too much!! Now, I am hoping it passes smog test in the morning!! I will reply the outcome tomorrow!

01-27-2011, 12:26 AM
Second attempt at smog test FAILED this morning!!!! Quick trip to muffler shop for a $220 Cat then back to smog shop. Third attempt finally passed with 0 NOX readings. Thanks everyone for all the advise. Much appreciated. I am sure I will be on here again with questions cause the car does have 250k miles. Hopefully later than sooner though!!

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