LWesthaver

I keep seeing EGR block-off plate kits for sale but have a question: Aren't three plates required to complete the job?

1. One plate for the exhaust port on the exhaust manifold.
2. One plate for the exhaust port on the intake manifold.
3. One plate for the EGR valve port in the intake manifold.

These kits only provide two plates. What am I misunderstanding about doing an EGR block-off???

Patsgarage

If you have a LT-1 this should work.
https://www.ebay.com/itm/EGR-Block-O...5.c10#viTabs_0

Benny42

LWesthaver

So you just leave the port on the intake manifold open?

Benny42

Yes. That hole in the intake can be left open. It only connects the exhaust tube to the EGR valve. With the EGR blank-off installed nothing will leak. I cut out a small aluminum plate to cover mine but its not required.

Mity2

BlueTwoToneCorvette

It stops the exhaust from coming back into your intake. It also can cause problems with the ECU throwing an error, or not throwing an error and then modifying the AF mixture in cruise mode, which can cause a lean condition. When I rebuilt my 85, I saw the black oily soot coating the inside of the intake and blocked mine off. I also reprogrammed the ECU to disable the EGR system, so the AF mixture is never modified, and no codes.

RedHot85Vette

I have an '85 as well. Stopped by the forum, with the question at hand, did a search, found this post and yours, got my answer inside of 60 seconds. Thanks to the asker, and Thanks to the answerer (?).

I'm off to eBay to get a nice block off plate.

John

BlueTwoToneCorvette

Thanks.
Sorry, but I think I wasn't clear in my previous post.
"It (The EGR block off) also can cause problems with the ECU throwing an error, or not throwing an error and then modifying the AF mixture in cruise mode, which can cause a lean condition."
At light throttle, the 85 ECU can enter a cruise mode with the EGR active. The AF is adjusted to balance with the EGR gas coming back in. When you block the EGR gas you get a normal O2 level in the intake air and this leans out the AF. The error code is related to the ECU emissions control when it senses that your EGR solenoid sensor is not active when it should be. A lean AF may also trigger another error code. I think the 86 and later ECUs had more complex emissions controls, and the 85 may not trigger a EGR fail code. This is why I reprogrammed my 85 ECU to disable the controls, as part of some other tuning I was doing. I think that the stock L98s run somewhat rich, so just blocking off the EGR like what you are going to do may not cause any real problems other than an annoying error code.