Smaller EGR stovepipe

[wlkjr]

I installed the smaller stovepipe included with my new plenum when I did the intake job last week. The larger one was completely stopped up. I'm wondering if the smaller one will clog quicker and what would cause that, maybe the EGR not working properly? Mine may not last long enough for that to be a concern again but I was wondering anyway.

[BNaylor]

Is your new one clogging? It takes time for stuff like that to clog up.

The purpose of the smaller EGR stovepipe is to prevent damage to the UIM composite material on '97 - '98 GP models with the NA SII 3800. The bigger stovepipe was causing the plastic to melt at the coolant passages causing coolant leaks directly into the intake system.

Unless you have any EGR related error codes setting off the SES light or other problems not mentioned I wouldn't worry about it.

[wlkjr]

I understand why they made the newer stovepipes smaller, but it is a significant reduction. My upper plenum did not show any melting around the stovepipe area and that was surprising to me.
I assume the EGR codes will appear when it starts to clog again. Clogging of the stovepipe may be the reason for the P0401 codes and not necessarily the EGR itself. Mine did set one 0401 code about 3 days after repair. I reset it and it has not come back.

[BNaylor]

Originally Posted by wlkjr

I understand why they made the newer stovepipes smaller, but it is a significant reduction. My upper plenum did not show any melting around the stovepipe area and that was surprising to me.
I assume the EGR codes will appear when it starts to clog again. Clogging of the stovepipe may be the reason for the P0401 codes and not necessarily the EGR itself. Mine did set one 0401 code about 3 days after repair. I reset it and it has not come back.

Probably just a fluke but I'd keep on an eye on it for possible return.

GM started using the smaller EGR stovepipes on all '99 and up models and they work fine. The only time I had a P0401 EGR flow problem which was in a '99 L36 GM car was when the PCV valve was not sealed properly due to a omitted black o-ring.

You should consider running an engine vacuum test to see how well the UIM/LIM job went just to be sure.

[wlkjr]

Originally Posted by bnaylor

You should consider running an engine vacuum test to see how well the UIM/LIM job went just to be sure.

How do I do that test? My old pcv valve seem to be pretty loose when I shook it so I assume it was ok and there was an O ring under it.

[BNaylor]

Originally Posted by wlkjr

How do I do that test? My old pcv valve seem to be pretty loose when I shook it so I assume it was ok and there was an O ring under it.

AZ or Advanced has the 0-30 hg automotive vacuum gauges for around $25-$30. You tee in off of any vacuum line like the ones coming off the throttle body. Good engine vacuum will range from nothing less than 15 in hg to about 22 in hg. Normally it stands tall around 18 - 20 in hg on a SII 3800. You do the test at idle and again at 2000 rpms and record the results.

[wlkjr]

Originally Posted by bnaylor

AZ or Advanced has the 0-30 hg automotive vacuum gauges for around $25-$30. You tee in off of any vacuum line like the ones coming off the throttle body. Good engine vacuum will range from nothing less than 15 in hg to about 22 in hg. Normally it stands tall around 18 - 20 in hg on a SII 3800. You do the test at idle and again at 2000 rpms and record the results.

While using my OBD scanning software with my laptop today, I make a new discovery. It reads not only engine coolant temperature but also the manifold absolute pressure. I don't even know what all this software will do.
At idle it reads about 11 and under acceleration it will go to about 23. It even gives a high, low and average. The high was 23, low was 8, and the average was about 14-15 as well as I remember. Think maybe I have a small vaccum leak somewhere?

[BNaylor]

Originally Posted by wlkjr

While using my OBD scanning software with my laptop today, I make a new discovery. It reads not only engine coolant temperature but also the manifold absolute pressure. I don't even know what all this software will do.
At idle it reads about 11 and under acceleration it will go to about 23. It even gives a high, low and average. The high was 23, low was 8, and the average was about 14-15 as well as I remember. Think maybe I have a small vaccum leak somewhere?

The problem is that will only be as accurate as the MAP sensor and what the PCM processes. The figures appear OK. However, MAP pressure is different from regular engine vacuum. I'd check engine vacuum first befoe deciding there is vacuum loss or a problem.