Today my 90 EX Auto Trans failed on the 25mph NOX reading and barely passed the 15mph. Here's the NOX numbers from the report:

15 mph-MAX 559, MEASURED 554 Pass

25 mph-MAX 516, MEASURED 778 Fail

The HC measured were 7 at 15 mph and 6 at 25 mph. The CO was zero.

California Car with 160,145 miles.
Oil changed at 160,000.

Tech said to check the EGR valve. So I pulled the valve and found minimal carbon build up, checked valve for movement and staying open when a vacuum is applied. All OK. Cleaned the passages on both the valve and the manifold. Replaced the EGR Valve gasket.

I asked the tech what the timing was and he said 17 degrees. I believe the spec is 15 degrees. Should I set it to 15, 14 or 13 to help it pass.

Valves have not been adjusted since 120,000 mile service but car idles smooth and runs excellent.

Anyone have luck with "Guarantee to Pass" by CRC that you add to your fuel tank. I have heard good things about it. Would it be wise to use it along with setting the timing back to 14 degrees.

The car only ran for about 10 minutes before the smog test. Next time I will run it for at least 30 minutes to get the Cat Converter good and hot.

Any other suggestions to help this 90 Accord to pass smog?

Thanks,
Gary

 

I'd back off the spark timing. It'll probably reduce your NOx but increase your HC & CO. There's a balance between those & I'd probably start at stock spec timing.

 

OK so today I checked the valve adjustment and all were within spec.

Replaced all spark plugs, cleaned dist cap contacts and inspected dist rotor. All are in good shape and the car idles and runs great.

I did retard the timing back to 15 degress, was at 17 when it fail smog at the 25mph NOX.

Now I notice that I have no vacuum at the EGR hose that goes to the EGR valve. I checked it at normal operating temp and above 2000 rpm.

Inspected all vacuum hoses for leaks and removed the vacuum control box mounted to the fire wall on Passenger side. Opened that up and everything looks good inside. No broken or disconnected hoses or wires.

I need to get this retested within the next few weeks. It failed smog on 4/18/11. See my 1st post for for test results.

What should I check next to determine why there is no vacuum available to the EGR valve?

 

Clean the EGR ports. There is a writeup in the DIY answers section. Also search the web for some good writeups.

Does the check engine light turn on or the D4 light start flashing? Have you checked for error codes? See DIY writeup on how to check CEL codes.

 

I did clean the EGR valve and the port area that it connects to. Not much carbon build-up in either. Would I have to remove the intake manifold to clean the runners?

The car will stall if I manually open the EGR valve at idle and also run rough when I do the same above 2000 rpm. So I believe that the intake ports are clean enough to supply exhaust gas.

I do not have a check engine light or flashing D. Could there still be a code stored? Should I check for trouble codes anyway?

The spark plugs were clean, normal tan color, but were worn and were due to be replaced.

Read some where that the ECU may not supply vacuum unless it senses the front wheels are rotating. Should I test for vacuum with the front end on jack stands and the car in drive...or run a vacuum hose to the drivers compartment and road test?

 

There are "plugs" on the intake runners that can be removed for cleaning....I think there are a total of five, one one each port to the head and another one towards the valve.

Yes, check for stored codes. I think the 90 had a led light on the ECU and TCU.

 

Checked for trouble codes at ECU and "Check Engine light". No codes stored.

Disconnected vacuum line to EGR valve,connected a 6 foot vac.hose and gage and road tested. No vacuum shown on gage. However during the road test I got a check engine light. Went home and read a code 12 which is "EGR System". Reconnected the hose and cleared the code 12.

Next I connected a vacuum tee to the EGR hose which is now connected to the valve. At the tee, I ran a 6 foot hose to a vac. gage and set that on the passenger seat. Road test and got 2 to 3 inches of vac at speeds up to 40 mph and above 1500 rpm. Vac was steady as long as I was accellerating. Vac would drop off as soon as I let up off the accelerator.

The car runs great with no performance issues and idles smooth with a steady 21 inches of vacuum.

I do not get any vacuum readings when vehicle is in park regardless of rpm. Only read vacuum during a road test.

I read that there should be @ 8 inches of vac available at the EGR.
I'm only reading 2 to 3''. Could that be because the vacuum tee is reducing the diameter of the hose plus the fact that I'm reading it at the end of a 6 foot length of vacuum hose?

With the car idling, I can apply a vacuum to the EGR hose and the car will die. Does that prove that the intake runners are clear enough and I should not have to drill out the plugs?

Unless I find other possible causes for my high NOX readings, I plan to:
1. Run this tank of "Guarantee to Pass" fuel to almost empty and then refill with either mid grade of premium. Which do you recommend?
2.Run the car for at least 30 to 45 minutes before the test. (last failed test was after only a 10 minute warm up).

Hopefully these 2 items along with setting the ignition timing back to 15 degrees from 17 degrees will bring the car within limits on the NOX.


Thanks to all that have replied for your suggestions so far.

 

The easiest solution would be to move to a better state.

 

I had same car and same problem here in TX. I removed the EGR plugs and cleaned the ports to solve the problem.

Not sure what to make of your vacuum measurements, however the system will set code 12 if inadequate vacuum is present to move the EGR valve.

Suggest cleaning the EGR ports. It's not that bad a job, but you will need a slide hammer to remove the plugs. New plugs are available from Honda. I managed to reuse mine by plugging the thru holes w/ epoxy. It is very difficult to avoid drilling thru one or more plugs. You will need new injector-fuel rail orings as old ones are likely to leak if reused.

good luck

 

This is a 1990 model.
The tech2tech TSB #013 says that on a 1990 model these plugs would not be present and to just drill a hole in the middle of the boss area. Then tap threads for the installation of a short bolt. In the article it does say that "some 1990s" have the plugs and all 91-93.
Was there a production date when they started installing the plugs?
I see a recess on the boss but not sure if it has a removable plug or it is a solid aluminum boss. I will drill and attempt to pull 4 plugs.