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EGR Valve info / help

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Post by 76Chevelle2Tone Tue May 24, 2022 3:27 pm

Yes the famous exhaust gas re-circulation valve that GM had all kinds of problems with starting with these years. Surprised that I could find no posts on this subject here. Maybe I searched wrong. The EGR valve on my car is working OK at the moment, but one thing I discovered about 15 years ago was that the settings for these EGR valves were modified years after the model was installed. What I mean is that GM would figure out years later and publish in an update what the correct settings for a given valve were. So I assume that could affect alternates/interchanges.

The issue I am having is trying to find interchangeable EGR valves or at least reasonably good alternates. There is a forest of different EGR valves listed in the Chevy Parts Manual and their installation patterns are very odd. The same model EGR valves could be installed in different Chevy models but also occasionally with different engines and transmissions over different years! Conversely two nearly identical car engines could have separate non overlapping EGR valves.
Below is what I found for installation on a 76 Chevelle with AT and 305 engine vs a 77 Chevelle with AT and a 305 engine:

Original 76 EGR valve: 7044090-17053964 – 305 V8: 76 Malibu All //
76 Camaro/Nova AT // 76 Monza Calif //
77 Camaro/Nova MT // 78 El Camino MT
\\ 350 V8: 77 Camaro MT

77 EGR Valve : 7045176-17055447 – 305 V8: 77 Malibu All //
77 Camaro/Nova AT// 78 El Camino/Camaro AT not Calif
//78 Impala not Calif \\ 350 V8: 77 Camaro AT

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Post by Joe73 Tue May 24, 2022 4:50 pm

Good info there. Most people delete the egr and not worry about it. It does cause a big build up of carbon in the plenum on the bottom of the intake manifold. I bet there isnt much overlap due to a difference in manifold vacuum differences engine to engine to make it operate. Me personally, if you want to keep your engine all original and your egr is defective, Id clog any vacuum lines to it to render it inoperable and forget about it.

On the same note, pcv valves are different engine to engine. And there is no chart regarding internal spring rates on any of them. Most people, if they use one which they should, just get a factory replacement for their make and model. If you changed your cam or rebuilt the engine, the factory pcv wont work correctly. Ive done alot of research when I needed a new one for my engine. The consensus was to use the late model pcv from the mid 2000s. It doesnt have a spring nor ball inside. Just a fixed sized hole on the bottom. Since a pcv is essentially a controlled vacuum leak, the fixed sized hole works perfectly. Thats what Im running on my engine with a large cam.
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Post by 76Chevelle2Tone Tue May 24, 2022 5:20 pm

Thanks for your reply. I understand what you are saying about variable vacuum differences but that was what surprised me when I examined installations. Chevy used the same EGR valve across disparate models and engines across different years. Conversely I don't think there was much difference between the 76 Chevelle 305 vs the 77 Chevelle 305. However they have separate EGR models.

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Post by Joe73 Tue May 24, 2022 6:50 pm

I believe it. Any idea if there was a change in the mounting area? Or just a physical change. Im willing to bet it was just a supplier change that looked different. Car companies change things mid run if they are running out and got a cheaper supplier.
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Post by 76Chevelle2Tone Tue May 24, 2022 7:16 pm

Joe,
The mounting for the 77 EGR valve referenced above fits the same way as the 76 valve. As to your point about blocking the lines, the first owner did that as I later found out. I bought the car over 30 years ago BTW. However I discovered it because the car wasn't really operating well. It worked better unclogging the lines and resetting things. I wonder if that technique works better on earlier models with EGR and not so well on these later years? Eventually I replaced the EGR valve about 25 years ago and it has worked OK since. But I am getting nervous about it. The 76 EGR valve is very hard to find. I was lucky to find the 77 valve in NOS form so I bought it without really being able to verify it will work if installed. I keep hoping Chevy had a book about the EGR valve permutations but haven't found a copy yet haha.

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Post by Joe73 Tue May 24, 2022 8:06 pm

I still think Id bypass it. Nothing good comes from hot oily carbon residue entering your engine.
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Post by zucchi Wed May 25, 2022 10:24 am

Some states are sticklers for emissions. For instance, Kommifornia requires smog checks on all 1976 and later cars with one requirement being the presence of factory emissions equipment. So, unless you live somewhere that has that sort of strict regulation, I would go one step further than what Joe73 recommended and remove it entirely and bolt a block-off plate onto the intake manifold. One less area that could develop a vacuum leak.
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Post by Joe73 Wed May 25, 2022 12:14 pm

Yes, states vary as to emissions but in actuality is against Federal law to mess with ANY emissions regardless of year and regardless of state. Not supposed to mess with it and its supposed to be kept in operating condition. But that is only if the vehicle will be operated on the road. I agree it would be best to just delete that egr but if you want to keep it original looking then plug it.
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Post by g3chevy / Mr Pontiac Wed May 25, 2022 12:27 pm

Joe73 wrote:Good info there.  Most people delete the egr and not worry about it.  It does cause a big build up of carbon in the plenum on the bottom of the intake manifold.  I bet there isnt much overlap due to a difference in manifold vacuum differences engine to engine to make it operate.  Me personally, if you want to keep your engine all original and your egr is defective, Id clog any vacuum lines to it to render it inoperable and forget about it.  

On the same note, pcv valves are different engine to engine.  And there is no chart regarding internal spring rates on any of them.  Most people, if they use one which they should, just get a factory replacement for their make and model.  If you changed your cam or rebuilt the engine, the factory pcv wont work correctly.  Ive done alot of research when I needed a new one for my engine.  The consensus was to use the late model pcv from the mid 2000s.  It doesnt have a spring nor ball inside.  Just a fixed sized hole on the bottom.  Since a pcv is essentially a controlled vacuum leak, the fixed sized hole works perfectly.  Thats what Im running on my engine with a large cam.

Joe, I concur with your thoughts on the OEM PCV valves. They don't work well with modified engines. This is what I ended up with when I built my 400 sbc for my 87 El Camino. They are a bit pricey at $130 but are totally adjustable.

http://mewagner.com/
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Post by Joe73 Wed May 25, 2022 4:44 pm

Cool. How did you check if it was functioning as per the engines needs? I know you could put a hose and vacuum gauge on the dipstick tube and you need to get a reading of 2-3 inches of vacuum. Having some vacuum within the engine definitely helps with not having leaks around the gaskets.

I went with GM part number 12572717 which was the updated pcv for the 99-2002 chevy engines that were having oil issues. It also goes under Standard Motor Products V372 as well as other part numbers. Its very common.

I hid my pcv inside an oil breather cap which still has the hose connection to the manifold. The cap is billet and has a snap ring on the bottom so you can change out the pcv whenever need be. Similiar to this but not nearly as expensive. https://www.motorcityvettes.com/earl-s-performance-pcv-breather-3434114erl. With my engine running, if I pop the cap off I can feel the suction on the fixed orifice so its definitely working. And I dont have any oil leaks lol.

Another thing I read when I was trying to figure out what to do for a pcv was guys were saying just use a pcv from a 69 Z28 with a 302. That engine has a big cam in it and its pcv was designed for it. I thought that could be an option but then I read about the fixed orifice so I went with that. There are absolutely no specs or charts relating to spring tensions or ball weight or size for pcv valves. Makes the decision way more difficult. Im sure most people are running a stock pcv and its not really doing much of a job for them with any engine mods.
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Post by g3chevy / Mr Pontiac Wed May 25, 2022 9:41 pm

There is quite a procedure to tune the PCV valve. Here's an overview.

HOW IT WORKS
 The Dual Flow PCV Valve can be in IDLE or CRUISE mode,
depending on driving conditions.
 IDLE mode has a low flow rate.
 CRUISE mode has an increased flow rate.
 The IDLE flow rate is controlled by the IDLE screw.
 The CRUISE flow rate is controlled by a combination of the user
set IDLE flow rate, and internal porting in the valve (porting is precision machined and is not user adjustable).
 The vacuum level where the valve switches from IDLE to CRUISE mode is controlled by the CRUISE screw (in Dual Flow mode)
TUNING METHOD OVERVIEW
Tuning recommendations are offered as a starting point, however the user may need to experiment to find what works best for a particular engine.
The Dual Flow PCV Valve can operate in Dual Flow mode or Fixed Orifice Mode. Two springs are supplied to accommodate various ranges of vacuum when operating in Dual Flow mode. Dual Flow Mode utilizes both the IDLE and CRUISE circuits. This mode flows a reduced amount of air under idle conditions and an increased amount of air under cruising conditions. The valve switches between flowing air through only one circuit (IDLE) and two circuits (both IDLE and CRUISE) depending on operating conditions. Two springs are available for use in Dual Flow mode. The high vacuum or low vacuum spring is selected based on the engine’s manifold vacuum level at idle. See “Selecting a Tuning Method” for more details. In the event that the springs need to be identified, the following length chart may be used. Note that the low vacuum
spring is a weaker spring (due to smaller wire diameter) even though its uncompressed length is longer than that of the high vacuum spring.
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Post by g3chevy / Mr Pontiac Wed May 25, 2022 9:45 pm

Joe, do you have any pics of your setup? Sounds like it would be a great alternative for folks who don't want to spend $130 on these adjustable valves. Also, I wasn't able to make the link work to the PCV valve you mentioned in your post.
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Post by Joe73 Thu May 26, 2022 10:46 am

Sure. here are a couple pics. I also found the billet pcv holder very similar to mine. And I also found one on jegs that is much smaller but I dont know if you can change the pcv like mine.

https://www.ebay.com/itm/401913388889?hash=item5d93e79f59:g:AXIAAOSwGJldmp-5&vxp=mtr

https://www.ebay.com/itm/313865781207?_trkparms=amclksrc%3DITM%26aid%3D1110006%26algo%3DHOMESPLICE.SIM%26ao%3D1%26asc%3D20201210111314%26meid%3Dd97b4fa2cd43442d82caca8446c14a23%26pid%3D101195%26rk%3D3%26rkt%3D12%26sd%3D403502578660%26itm%3D313865781207%26pmt%3D1%26noa%3D0%26pg%3D2047675%26algv%3DSimplAMLv9PairwiseWebMskuAspectsV202110NoVariantSeedWithRevOpt90NoRelevance&_trksid=p2047675.c101195.m1851&amdata=cksum%3A313865781207d97b4fa2cd43442d82caca8446c14a23%7Cenc%3AAQAHAAABIFVvFeUTQhL4KP79koL%252B4Ydgokeb2CQrAyC%252BOwbdpQetV2qAC7C3Vu0XLY04JD2l73LYnMyfSHCKvxS7d%252F15SZlydoOOGTzprPO8qZrjfCQtOuzZwI0WDIexQZ2VQztoEUgq2TzXv%252BOtZ48Pe5gHGHxqo%252FGx9Dt7QZhFprTZu6mVv0mDUCc7q85TJtj%252Fmjddv%252FfG2pxfoEwL%252B0pFCg%252BvLkaa4rERUeLvpueRk8CJrhSqoQKdIgvZHq0GqKvlS1Qejl79mmmbRh3Y%252Ft5P3Wbwto%252FqSxNclvwhtGNZGlGeiWSCoaCxiyx629WSWAj3FXidwNBGUZraC%252F9GCCy5DhHFlHM3F5ziQ%252FCliKfo7Zoh1LGQ485LUOVsKkrm0CjgRCFxHQ%253D%253D%7Campid%3APL_CLK%7Cclp%3A2047675&epid=12012799100

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Post by g3chevy / Mr Pontiac Thu May 26, 2022 10:57 am

Cool, so this is a PCV housing that you installed your own PCV valve into?
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Post by Joe73 Thu May 26, 2022 11:00 am

Correct. Thats what its designed for. Took me awhile to find it because I wanted to use the fixed orifice pcv. And for me, it doubles as my oil fill port in the valve cover. I running tall cast aluminum covers so I drilled the hole on the drivers front and the passenger rear so I can have the same setup like factory. PCV on drivers front and air cleaner breather on passenger rear. Has something to do with the rotation of the crankshaft to have them in those positions so Ive read. Its been working well for me.
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Post by g3chevy / Mr Pontiac Thu May 26, 2022 11:21 am

Good info. Do you also have a breather from the valve cover attached to your air filter housing for your carb? Do you have any pics?
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Post by Joe73 Thu May 26, 2022 12:02 pm

Yes, like I mentioned above.  Pass side goes direct into the air cleaner just like factory.  Something to do with the rotation of the engine is why it was designed with breather on pass side and pcv on drivers.

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Post by g3chevy / Mr Pontiac Thu May 26, 2022 9:36 pm

Oh, okay. Do you have the breather tube on a filter? Or does it go straight into the carb without being filtered?
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Post by Joe73 Fri May 27, 2022 5:49 am

Straight into the air cleaner base, no filter.
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Post by g3chevy / Mr Pontiac Fri May 27, 2022 11:08 am

Okay, cool. Do you think that would be an issue on a throttle body fuel injected engine?
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Post by Joe73 Fri May 27, 2022 11:10 am

I wouldnt think so at all. My setup is exactly how gm had it from the factory. Pcv drivers front to the baseplate or below the carb/throttle body. And the pass rear valve cover to the base of the air cleaner.
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Post by g3chevy / Mr Pontiac Fri May 27, 2022 11:41 am

That's was I was thinking. It shouldn't affect anything but it doesn't hurt to ask. Also, my factory air cleaner on my 75 Laguna has this breather filter in the air cleaner. Is yours different?

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Post by Joe73 Fri May 27, 2022 11:44 am

I did not use a filter inside the air cleaner. That one in your pic would go to the side of the air cleaner. I bet you can make it work with an aftermarket air cleaner base but I dont see a need for it. My stock 73 air cleaner has that little filter on it as well, I think most years had it.
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Post by g3chevy / Mr Pontiac Fri May 27, 2022 12:23 pm

Okay, thanks for the feedback Joe.
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Post by Joe73 Fri May 27, 2022 4:46 pm

Anytime at all.
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