Questions and Answers

Honda DX EGR Passage Blocked Q. Question: When the EGR valve is removed from the engine of the above described car, does the exposed 1cm x 2cm rectangular hole in the intake manifold, constitute a leak, and as a result of the leak, the engine might not even run, and if it did run it would run very poorly? 1988 Honda DX 2.0 liter Automatic transmission 340,000 miles P/S, A/C, Cruise control

For additional background: I have a 1988 Accord DX. I bought it new. It has been very dependable. As it has past 340,000 miles, its dependability has faded a bit. I want to keep driving it because it deserves it. It deserves the gentle driving it gets and the care.

During California Pre-Smog test, it passed everything except the EGR System test. It failed the pretest because it did not run poorly when the test mechanic manually opened the EGR valve. (He reached in and lifted the vacuum operated diaphragm causing the valve to open.) His suggestion was that I remove the EGR valve, clean it, and clean the system as best as I can. I am doing that now.

The first thing I did was remove the EGR valve and checked it for functionality. It opened and closed with mouth imposed vacuum. The valve seat closes with a positive seal, and appears to do what it was designed to do. The diaphragm does not leak; I opened it the same way he opened it, by manually forcing the diaphragm open, and putting a rubber plug over the vacuum opening for 45 minutes. I also cleaned the steel pipe from the exhaust manifold to the intake manifold. Those particular components looked okay.

At this point I reasoned that there was a very large hole in the intake manifold, where the EGR valve had been, and that if I tried to start the engine, it would not run very well, sort of like it was not supposed to run very well in the EGR valve functionality test. I blocked off the open vacuum tube that normally fits over the EGR valve input, and started the engine. It ran okay.

The pipe from the exhaust manifold was spitting out exhaust gasses and heating up everything around the point of termination in the intake manifold, so I could not allow it to run very long, but is this normal? With a large leak like that, in the intake manifold, how could the engine even run?

I reasoned then that there was no leak even though I could see the uncovered passageway into the intake manifold. I had to somehow figure out a way to determine if there indeed was no leak at that location. The opening was rectangular about 1 cm by 2 cm.

I picked up a rubber hose and forced it into the hole and packed plumbers putty around the edges, and started the engine. I think I detected a very small vacuum, but not near as much as would be expected on an intake manifold. I think now that I was mistaken; there was no vacuum.

At this point I do not have enough experience with the function of EGR systems to guess what to do next. My reasoning tells me that carbon deposits from the EGR system, have built up to such an extent that a blockage exists in the manifold casting, or during a recent blown head gasket and replacement of intake and exhaust manifold gaskets, something is in there blocking the way.

I sure hope it is not necessary to remove the entire intake manifold. Can you speculate on any of this?

Yours truly,
Gene

A. Removing the EGR valve does leave a hole in the intake manifold causing a massive vacuum leak. The exhaust gas coming out is normal. This is where the exhaust that is recirculated comes from.

You are right in that an intake manifold with that bog of a leak will not run very good, if at all. But if the EGR passage inside of the intake manifold is clogged, or partially clogged, that would effectively seal the vacuum leak.

Since your EGR passage takes a 90° turn, it won't be very easy to clear out without taking the intake manifold of. And it is quite possible replacement may be the only way to fix it.