My '91 Accord Wagon has over 367k miles. It's passed California smog every time as long as I do a tune-up first. Last check, 2 yrs ago, I was lazy and it failed due to high NOx levels. Smog tech blames EGR. Later I checked EGR, replaced it's gasket, did a tune up with Denso and Bosch parts, ran some CRC emissions cleaner through, went back and it passed. I've put about 7k miles on it since then as it's just a spare vehicle for us for a while now. I keep thinking of selling it and probably should have last time it passed, but it just drives so damn good. I'll still drive it on the occasional weekend to keep the tires from flat spotting and knock out the cobwebs.

So prior to this smog check I ran some CRC emissions cleaner through, following all the steps again, ran Chevron 91 through for a while after the cleaner. Got it nice and warm for the test but had to wait probably 30-40 min (this part I forgot until after I got home). And it failed again due to high NOx. Of course the "tech" blames the EGR again. Once I'm home I double check EGR function and it's fine. Vacuum hoses are all fine. Plugs looked good as well as cap and rotor inside. Only thing looking suspicious is some oxidation on the little button that the coil spring sits on in the coil pack. The coil spring actually made an escape when I removed the cap and I don't remember if it's just resting there or stays attached. Honda does sell that spring separately. But mine looks fine otherwise.

I had cleaned out EGR passages (yep the hard way) at 358k miles in 2017 when I installed a rebuilt head due to a minor coolant leak in cyl 1 or 2. It passed smog without issue twice after that. 90% of my driving is freeway and this thing is almost butter smooth except for my damn aftermarket cv axles. And acceleration is always strong. We always keep Shell, Chevron or Mobil 89 octane in it.

So my question is, can not getting enough use in 2 years be the issue? I had NGK copper plugs in it, and I'm considering the Iridiums if I decide to change everything again for the retest. Was it possibly cooled down to much by the time it got tested? Is it possible the catalytic converter is finally done? Yes, maybe, I know, but I'd figure if it was I wouldn't have gotten it to pass last time. And I don't want to just throw and expensive part at it unless I know for sure. Cheapest CARB cat I found is a Walker for $375. Magnaflows are stupid expensive and I haven't found the BR Exhaust version yet, if there is one. I know BRs can be way cheaper despite just being Magnaflows without the label.

Any thoughts?

Thanks in advance,
Chris

PS, I know the test says N/A on functional EGR. But it's always said that on the passing tests in the past too. I don't know why that is. And last test prior to this one, the NOx failed at 999 then passed at 750.

'91 Accord Wagon LX 367k miles

 

I got the NOx down but it failed the evap test.

So I changed out my 2 year old copper plugs for iridium, and changed dist cap, rotor, wires, PCV valve and air filter. I also ran some Lucas NOx treatment through most of a tank of fuel. That got it to pass the tail pipe emissions but this time it failed the fuel system evap test. Tech said it just barely failed. It had passed on the first test just fine and every test prior to these. He even rechecked his system and tested twice. He thinks it must be a cracked hose in the evap system. But every hose I can get my hands on feels fine. I had the car parked for a couple hours and there was a hiss from the fuel cap when I removed it. I've got the emissions control box out of the car and open. All hoses look fine (love the old Honda hose material). I had checked hoses at the tank as far as I could see and they look and feel fine.

Any ideas where to check or test next?

 

OK, I did some vacuum testing it seems the Purge Cut Solenoid Valve (36166-PE7-662) is allowing some vacuum to escape. It connects to the top of the charcoal canister. I'm not familiar with these old emissions systems as I usually work on industrial equipment and motorcycles. So any insight as to if I'm on the right track or not will be greatly appreciated.

Edit - It looks like this part is discontinued. I wonder if I could run a little silicone lube through it to help revive any seals inside might help?