If you have a high mileage Accord and have never cleaned the EGR manifold, you should consider this maintenance. All Accords from Yr 90 through 97 have an exhaust gas manifold that distributes exhaust gas from the EGR valve to each intake tube of the intake manifold. Years 90-93 have a one-piece exhaust distribution and intake manifold w/ plugs to access the exhaust gas ports into the intake manifold. From 94 on, the exhaust distribution manifold is bolted to the top of the intake manifold and is much easier to access for maintenance.

Sometimes the exhaust gas ports into the intake manifold become selectively blocked resulting in too much exhaust gas to some cylinders. This results in an excessively lean mixture and a "sag" when you attempt to accelerate. There is a TSB on this condition and it is a common problem.

I have a 94 Accord EX w/ 188K miles which was running fine w/ no performance or drivability problems. However, it was taken in for an emissions test in Harris County, TX and did not pass the emissions test. It failed the low speed 15mph CO% 4.85% (standard 0.73%) and the high speed 25mph NOx ppm 1348ppm (standard 910ppm).

I performed the following checks and maintenance:
1) New Air Filter, 2) Checked & Cleaned PCV, 3) checked O2 sensor (good), 4) Cleaned and gapped spark plugs, 5) Set timing to spec (15 deg BTDC), and 6) removed and cleaned EGR manifold, EGR intake manifold ports, EGR valve/passages.

I found the EGR manifold almost entirely blocked w/ carbonized material, all 4 ports were completely blocked. EGR valve was dirty but open.

Accessing the EGR manifold requires partial removal of the fuel inlet manifold and injectors. I disconnected the fuel supply line from the fuel manifold and disconnected the fuel manifold w/ injectors attached from the intake manifold. I moved the fuel manifold w/ injectors to one side to allow access to the EGR manifold. There are a number of vacuum lines that must be released from the fuel manifold assembly to allow relocation. I also reomved a vacuum solenoid mounted on the throttle body to gain further access.

Once the fuel manifold is relocated and fuel manifold support studs removed, the EGR manifold is released by removing 5-10mm socket size bolts.

Cleaning the EGR manifold required throttle body cleaner, Chemtron solvent, and high pressure water blasting to throughly clean. The exhaust gas ports into the intake manifold were cleaned w/ a small screwdriver to clear the upper port, and a drill bit slightly smaller than the port passage to manually drill through the carbonized material. I held a shop vac near the operation to recover as much as possible of the crud. There was a depth of a ~6mm of crud in each port completely blocking exhaust gas into the intake manifold.

After the maintenance, the car was successfully retested w/ following results on the previously failed tests; Low Speed CO% 0.42% (standard 0.73%) and High Speed NOx 281ppm (standard 910ppm).

There was no change in performance or drivability.

I next plan to attack my high mileage (~ 265K) 90 Accord EX which has never had the EGR manifold maintenance.

Regards

 

good post, you should throw some pics in there and you'll have an excellent write-up.

 

Is there any CEL present because of the EGR clogged up?

 

No, either partial or complete blockage of the ports will not set the CEL. In my case, the only indication was the High NOx from the failed emissions test. EGR system is designed to reduce combustion chamber temperatures which reduces NOx. In some cars, the combustion temps will get so hot that pre-ignition occurs and you get severe pinging w/o EGR. I never noticed this w/ the 94 Honda.

regards

 

If you have a 1990-1993 Accord, you will need a fine drill bit. You will also need 4-6 of part number 17199-PT3-AHM from your local Honda Dealer, they are the port plugs.