Writing a guide on EFI EGR system troubleshooting and need some help with images

Hello to all,

I've been away for a long while (long story and irrelevant to the posting)

When I first got my 1968 LX-i it did not pass smog because of high NOx. A code 12 was flashed by the ECU LED.
Did not have a service manual covering the EGR system, so it took me a while to figure it out how it worked. I eventually fixed it and never gave problems again
So, I have that knowledge sitting in my head doing nothing and I decided to write a guide explaining what the EGR system does, how it works, its components, and how to test using regular tools.

The service manual I later sourced provides lots of information but unless you have some special tools listed there some components cannot be tested thoroughly.

What I would ask is if anyone has a spare black box sitting around in the garage or shed and want to take some photos of its innards I will include those that are part of the EGR system -basically, everything that is attached downstream of hose #24. I am describing them in words, but one image is worth a thousand words (as the saying goes). The 1986-87 and 1988-89 have slightly different EGR systems inside the black box - different solenoid and slightly different hose arrangements. Although I will write about my car (1986) I am aware of the differences and will include some references to them. Images would be invaluable to highlight those differences and support the text

I am still working on it so there is no need to rush. Once it is done i will open a thread and post text, images and a couple diagrams. A late draft of the very introduction is below

Thanks in advance.

What the EGR system does
Exhaust gas recirculation system (EGR) reduces oxides of nitrogen emissions (NOx) by injecting a bit of exhaust gases back into the intake manifold, which lowers the temperature inside the combustion chamber in each cylinder below the limits of oxides of nitrogen(NOx) formation.
The system is controlled by the ECU via a solenoid inside the black box that uses intake manifold vacuum to command the EGR valve. The valve has electrical connections that tell the ECU its position (how open it is) via the three-wire connector attached to the EGR valve. The EGR valve is located close to the distributor on the intake manifold side of the engine.

Thus, the system’s operation uses
a) exhaust gases
b) engine vacuum (from intake manifold)
c) electricity(solenoid operation and EGR valve signals)

The ECU will ONLY flash a code when there is a problem with b) or c).
Problems with a) may not trigger a code - only OBDII cars have EGR flow/temperature monitors which our cars do not have. However, the car will fail the NOx part of the emissions test WITHOUT a Code 12 fault in the ECU.

Emission failures under a) will not be covered here. As a first approximation, those failures may indicate a problem with blocked EGR passages somewhere from the exhaust manifold to individual intake runners to each cylinder. In particular, blocked individual intake runners is a problem that happens with several generations of Accords (google Accord blocked EGR passages). It is unlikely all four of them will be blocked simultaneously, however. The pipe connecting the exhaust manifold to where the EGR valve sits in the intake manifold may be another source of blockage (it supplies exhaust gases to the EGR system); a clogged (but not stuck) EGR valve is another possibility.

This guide will deal with b) and c),specifically with what happens inside the engine bay and the black box. Wiring issues such as connection between the EGR valve and EGR solenoid and the ECU will not be addressed here - they can be dealt with using the service manual.
The diagrams and explanations cover mostly 1986-87 fuel injected (LX-i) Accords. 88-89 EFI Accord (LX-i, SE-i) have a different solenoid valve and a different air chamber; however, the general principles of operation and values are the same. They should be applicable to 2nd generation EFI Preludes as well - they do have the same A20 engine as the 3G EFI Accord

I did a cut and paste job from the book years ago here trying to help someone. Go ahead and copy that if need be.

Welcome back!

If the egr valve tests good with a vacuum pump, it’s almost always the same cause for the light and code. The little white chamber inside the black box gets plugged up. Take it out and clean each port, there are 3 if I recall correctly. It’s most commonly a problem on 86 and 87 for some reason.

Welcome back Gabe!

I'm pretty sure this is an 86 87 black box... couldn't find a hose labeled 24 tho

https://www.facebook.com/media/set/?...1&l=b54537163b