Won't start when hot and NoX Issues ('86 Accord DX)

[crazylikeacat]

For the second time in a month, my car (manual 5 speed, LX (err not DX in title)) failed smog as a gross polluter thanks to high NoX. The other emissions are very low.

After the first failure, was told to replace the EGR control box. The replacement remedied a weak vacuum they thought was the problem, but the NoX levels didn't come down.

It also doesn't start when hot, although it cranks; or else it starts but dies quickly at low speed. This only happens after a lot of driving and idling on a hot day, ie. after a "hot sit."

Some measures were taken to rule out ignition and the fuel pump: one of the spark plugs was visually tested and it sparks. Propane was poured directly into the air intake while it was cranking, but it still didn't start.

At 25mph NoX falls dramatically to passing levels (from 2,314 to 477 ppm). It fails at 15mph.

Other than the hot start issue, it runs with superb efficiency. The foot barely touches the accelerator and it sails along at 70mph.

Am I dealing with two issues or one? What are the usual culprits?

thanks in advance!
m

p.s.
It's not the fuel-injected model, so it can't be the main relay issue that affects those models. Also, there's no ECU code panel as with the '86 LXi.

[A20A1]

If you say already tested EGR then here is some other possibilities.
http://www.3geez.com/forum/showpost.php?p=846373&postcount=7
There is some help with emissions in that post.

Vacuum leak, or pre cat Exhaust leak?
Useful items to help detect leaks.
- Carb Cleaner (Intake/carb)
- Soapy Water (Exhaust)
- Flour or baby powder (Exhaust)

Bad Air Suction Valve?
- Check if the valve is functioning properly.

http://i23.photobucket.com/albums/b351/Wendy_girl/asvalve.png

Warm up the engine and remove the silencer tube (#8 in the image above) or just remove the air cleaner lid. At Idle there should be a bubbling sound from the rubber coupling at idle (#10 in the image above) or from inside the air filter. If you hear a bubbling sound, disconnect the vacuum hose #5 to the air suction valve (#2 in the image above) and plug the hose, the noise should stop. If you still hear bubbling with vacuum removed from the valve then the air suction valve is bad. Connect a vacuum gauge to the #5 line, if there is vacuum at idle the AS is controller should be okay.


Here is where the solenoid for the AS valve is located. #5 & #24
http://www.3geez.com/forum/attachment.php?attachmentid=4543
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EDIT:
Here is the part I wasn't sure about, but after looking at the manual, I see that above 2000 RPM, vacuum should not be present at #5 vacuum line to the AS valve, and the bubbling sound should stop. Question is at 15 MPH, what is your engine RPM? If it's above 2000 and you are still getting fresh air from the AS valve it could throw off emissions, and cause a lean condition which would mean hotter engine temps.

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[Dr_Snooz]

High NOx is almost always a problem with the EGR. I would guess that either the valve is sticky or the channels are all coked up, but other things could be haywire too. There are a series of tests in the manual (http://honda.roadpwnage.com/manuals/pages/usdm-accord-1989-full.php) for checking it out. Be aware that the manual is for the '89 model year which is somewhat different from the 86/87 model years. I'm not sure what year yours is. If all the manual tests check out, then pull the valve and check its function. Also look for carbon in the manifold channels.

[crazylikeacat]

Thanks for those leads which I'll pass on to my baffled mechanic.

I'll report back when I have answers.

[crazylikeacat]

Thanks for the help.

A20A1's diagram convinced my mechanic that the new EGR control box was not the same model as the one it replaced. The new box will go back to the yard, the old EGR box will take it's former place. Hopefully, I can fix it by cleaning it - that's the subject of a new thread.

-m

[A20A1]

Snooz Mentioned that there are differences in the years. I don't know what they are since the only control box I've opened was an 89, I owned an 87 too but I never looked into the it's box. I do know the image above was from an 89 because it matches my box.