I got a 91 honda accord failed smog diag, @15 failed for high NOX @ 25 clean across. There is also hesitation surging from 10-15 mph. I found #1 cylinder misfiring i found plugs were foul and oil soaked from tube seals, I replaced plugs wired and VC gasket. I checked egr function and it works fine, valve holds vacuum i pulled valve and ports seem clear i ran motor had good suction from intake port,i teed vacuum gauge into vavle and it seems from 10-15 mph i have full egr effect and no codes, i suspect the map sensor or egr solenoid is open all the way instead of fluctuating the vacuum properly any ideas?

 

EGR pulling a vacuum doesn't mean that all the egr ports are open. Some could still be clogged.

Did you pull the plugs on the intake manifold and clean the egr ports?

In the common diy thread on top of the gen tech help forum, there is a link for cleaning 4th gen accord egr ports.

Also google T2T013.pdf. The first part shows how to do this as well on your accord.

 

im almost positive all ports are clean, i did a test and held rpm at 2g and held egr valve open and if you pull plug wires 1 at a time if there is no suggnificant drop in rpms that port is most likely plugged, they are reacted fine( good drop in rpms). the egr valve was clear and the first 2 ports were clean so im assuming the last 2 ports are clean, and its not easy to get a customer to cough up that much to drill out their intake to check suspected plugged ports, like i said my emissions were good all at 25 but at 15mph it failed for high nox and has surging stumble, with egr unplugged it runs fine

 

if it runs fine with the egr unplugged that should be your answer. take off the intake plate for your egr ports and clean them.

you must be the shop doing the work? if so it is not hard to pull the plate to clean egr ports.

maybe 30 mins.

faulty egr valve and or the egr passages will cause the surging idle and high NOx emissions.

 

You may have some ports plugged and others open. The ports are usually the problem when high NOX is indicated. Also clean EG delivery channels.

good luck

 

i had the egr off and valve and ports i could see were clean no build up at all i even tried to clean out but got nothing, when i ran my post test it passed freakn miracle, and he was a test only so i sent him on his way and he passed there too. maybe a intermittent egr valve postion sensor telling pcm that its not open so it opens it more which is too mch egr at 15 mph causing stumbling misfire.

 

i know the problem is in the egr, but why it was getting full egr effect at 15 mph i have not a clue i didnt get a lot of time to diagnose and was already over in my time on the car, i had already 500 n repairs fixing the customers bro f-up, he cross threaded #1 plug, tube seals leaking filled the spark plug tubes with oil the wires were swelled.