engine vacuum issue
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Joined: Sep 2011
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From: Strasburg, Pennsylvania
Car: 1991 Chevrolet Camaro Z/28 (Project
Engine: 5.0L 305
Transmission: 700R4 W/ B&M shift kit
Axle/Gears: 3.23
engine vacuum issue
I realized with the high flow exhaust system (edlebrock headers,3 inch tubing,high flow cat, and flowmaster muffler) there is no longer enough vacuum to open it i was wondering if there is a a way to boost up the vacuum enough to have the valve functioning again with out sacrificing anything in the exhaust or any major engine work
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Joined: Mar 2008
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From: CT
Car: 86 T/A, 83 Z/28
Engine: 5.0 TPI, 350 2 X 4 bbl
Transmission: 4 speed auto, 5 speed manual
Axle/Gears: 3.23 posi, 3.73 std
Re: engine vacuum issue
I'm going to go ahead and take a guess your talking about the EGR valve? What type of EGR valve do you have positive or negative?
Thread Starter
Junior Member
Joined: Sep 2011
Posts: 46
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From: Strasburg, Pennsylvania
Car: 1991 Chevrolet Camaro Z/28 (Project
Engine: 5.0L 305
Transmission: 700R4 W/ B&M shift kit
Axle/Gears: 3.23
Re: engine vacuum issue
the egr valve runs off of the intake vacuum as well as the negative back pressure in the exhaust system however with this highflow exhausts system has reduced most of the negative back pressure so i need to find a new way to make up the lost back pressure vacuum to have the valve able to open during operation
Thread Starter
Junior Member
Joined: Sep 2011
Posts: 46
Likes: 0
From: Strasburg, Pennsylvania
Car: 1991 Chevrolet Camaro Z/28 (Project
Engine: 5.0L 305
Transmission: 700R4 W/ B&M shift kit
Axle/Gears: 3.23
Re: engine vacuum issue
im going to assume that it is a negative valve as it runs off the back pressure of the exhausts but i could be wrong
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Supreme Member
Joined: Mar 2008
Posts: 1,549
Likes: 1
From: CT
Car: 86 T/A, 83 Z/28
Engine: 5.0 TPI, 350 2 X 4 bbl
Transmission: 4 speed auto, 5 speed manual
Axle/Gears: 3.23 posi, 3.73 std
Re: engine vacuum issue
Actually I believe you have it backwards. A positive type EGR valve requires positive pressure in the exhaust system to allow the EGR valve to operate. When positive pressure is applied to the EGR valve it closes a vent inside the vacuum diaphragm so that engine vacuum can open the valve. With a high flow exhaust sometimes you can’t build up enough positive pressure to plug this vent so the EGR valve will essentially never work. Negative type EGR valves work in the opposite fashion (negative pressure) and don't seem to have this issue. Now without really knowing what type of EGR valve you actually have what drew you to the conclusion that this is the problem or that you even have a problem for that matter?
Thread Starter
Junior Member
Joined: Sep 2011
Posts: 46
Likes: 0
From: Strasburg, Pennsylvania
Car: 1991 Chevrolet Camaro Z/28 (Project
Engine: 5.0L 305
Transmission: 700R4 W/ B&M shift kit
Axle/Gears: 3.23
Re: engine vacuum issue
i quess i could find the part number and try to find the opposite pressure than the one i have and hope it works
Thread Starter
Junior Member
Joined: Sep 2011
Posts: 46
Likes: 0
From: Strasburg, Pennsylvania
Car: 1991 Chevrolet Camaro Z/28 (Project
Engine: 5.0L 305
Transmission: 700R4 W/ B&M shift kit
Axle/Gears: 3.23
Re: engine vacuum issue
the valve not opening at all due to not enough back pressure and my ses light poping on when i hit 50mph but mine has an N stamped on it so im going to try a positive one to see if there is a difference
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