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92 Honda Accord Won't pass Emissions

We have a 92 Honda Accord 2.2L We have been trying to get it to pass emissions since October. So far we have replace the gas cap, replaced the O2 sensor and replaced the EGR valve. Here are the readings
25/25 test 50/15 test
HC ppm 17 29
CO% .07 .20
NO ppm 1162 1230 after replacing the O2 sensor but before the EGR the 25/25 side passed reading 1005
CO+CO2 % 15 15

Can anyone give us an idea of what is going on and what the next step is we should try?

You car appears to have a carburetor, the numbers are not cleat what is going on but assuming it is incomplete combustion. A good dose of sea foam and some new plugs, 100 highway miles and make sure the car is warmed up would be the first thing I would try if it were mine. After that looking at basic components distributor cap, plug wires, etc. Instead of throwing money at it a good repair guy can analyze it.

No Accords after 1989 had carburetors.
Make sure the EGR ports are clear.
Does the check engine light stay on?

It would be more helpful if you posted the measured value for each type, compared to the maximum allowed.

Is it failing on the HC, the CO, or the NO component? It appears from what I see the NO is your only emissions problem. The HC’s look good, and the CO appears to be maybe a little on the high side, but still probably within the limit. Am I interpreting your numbers correctly?

If the problem is the NO … The EGR is what primarily controls the NO emissions. NO’s are caused by high combustion temps. Which occur on heavy acceleration. The EGR cools the compustion chamber by routing exhaust gas back into the intake manifold. If it did this all the time the car would run poorly. So it only engages fully during heavy acceleration. It is usually controlled by a vacuum signal originating in the throttle plate area. And there is usually an associated device which prevent the EGR from operating until the engine coolant is at normal operating temperature.

The thing I do to test that the EGR on my early 90’s Corolla , I hook up a vacuum pump to the EGR vacuum control, at idle, when a vacuum is applied, the engine should sputter and possibly stall. If it isn’t, then while your EGR device may be working, the EGR passages that the device connects to may be carbon clogged.

If the EGR works, then it is possible the gadget that only allows the EGR to operate when the coolant temp is high enough is failing. That device should pass the vacuum through when the coolant is at operating temp.

It’s always a good idea to bring all the routine engine maintenance suggested in the owners manual up to date before emissions testing. Especially the engine air filter. I usually put in new spark plugs and set the ignition timing to spec too. If you Google “How to pass an emissions test” there are a couple of good web sites that offer some tips to increase your chanced of passing. Best of luck.

With HC that high (unburned fuel) that indicates something isn’t burning in comb chamber. I’m surprised you don’t have a miss code. New plugs, wires, cap, rotor, ensure All vacuum and elec connections are good. New air fitter. That should help bring your HC down

@bennyandthejets This car is not OBD2. OBD1 PCMs weren’t that sophisticated when it came to turning on the MIL, setting codes, etc.

I agree with the others about checking the EGR operation.

Internet error, no carb, but same advice applies

High NOx readings can also be caused by a lean mixture which in turn might be caused by a simple vacuum leak. Check all vacuum hoses and vacuum operated devices.

If these emission readings are being taken at idle, then the EGR is not involved. The EGR doesn’t kick in until above-idle engine rpms.

As AlanY noted, make sure you have no vacuum leaks.

What state do you live it? In MD, you need to make a real effort to fix the problem. But after paying a certain amount, you can get the smog test waived after you show them the receipts. Maybe it is the same where you live.