EGR Valve and Vacuum Advance Testing - The 1947 - Present Chevrolet & GMC Truck Message Board Network

cgrossl · 11-03-2003, 10:41 PM

I just bought a 1985 Chevy Custom Delux with a 305 in it a few weeks ago. Ever since I have bought it, it has had a hesitation at tip in. So, I immediately started looking for vacuum leaks. So far, I have replaced most of the vacuum lines because most of them have dry rot in them. Some were broken and fell off of their connections. All of this has helped, but the hesitation is still there. So, I hooked a vacuum pump to the EGR valve and I found that it had a slow vacuum leak. Is this normal? I wouldn't think that it would be, but I don't really know. I also tested the vacuum advance canister. I can't get it to hold any kind of vacuum at all. Just as soon as I get done pumping, the gauge goes right back down to zero. I wouldn't think that this would be normal either, but I am just checking to be sure. Is this normal?

I am thinking that I need to replace the EGR valve and the vacuum advance canister. Would everyone else concur? Or, can I get rid of the EGR system (no emissions testing here) all together and still run on 87 octane gas?

Russell · 11-03-2003, 11:02 PM

I don't think that your vac advance is suppost to let it all out... One way to check if it is working is to hook up a timing light and have someone rev the engine while you time it, you should see the timing mark moving off to the left while you accelerate the engine...

I took the EGR unit off my truck, all it does is make it run a little worse for the first ten minutes or so in cold weather... I would suggest leaving it in if you can...

bigd65 · 11-04-2003, 06:19 AM

if eather of them loose the vacuum load, they are bad and have cracked diagfram's (wow, i miss spelled that) as far as the EGR and if you can run without it. if i'm not mistaken and from speakin from experience. if you keep your old manifold you will need to keep the EGR to be able to run on 87 octane,because of the exhaust crossover under the intake. now if you change to an intake, like the AIRGAP's, they dont have the exhaust crossover under the intake, therefore no EGR. without the crossover under the intake, it keeps the intake cooler, therefore a denser fuel charge and can still run 87 octane

**swervin ervin** · 11-04-2003, 11:30 AM

Check the accellerator pump in the carb. With the engine off and warm, make sure you are getting a steady stream of gas in each primary when you slowly open the throttle by hand.

Oh, and, welcome to the forum.

11-03-2003, 10:41 PM	#1
cgrossl Registered User Join Date: Oct 2003 Location: Lexington, KY Posts: 151	EGR Valve and Vacuum Advance Testing I just bought a 1985 Chevy Custom Delux with a 305 in it a few weeks ago. Ever since I have bought it, it has had a hesitation at tip in. So, I immediately started looking for vacuum leaks. So far, I have replaced most of the vacuum lines because most of them have dry rot in them. Some were broken and fell off of their connections. All of this has helped, but the hesitation is still there. So, I hooked a vacuum pump to the EGR valve and I found that it had a slow vacuum leak. Is this normal? I wouldn't think that it would be, but I don't really know. I also tested the vacuum advance canister. I can't get it to hold any kind of vacuum at all. Just as soon as I get done pumping, the gauge goes right back down to zero. I wouldn't think that this would be normal either, but I am just checking to be sure. Is this normal? I am thinking that I need to replace the EGR valve and the vacuum advance canister. Would everyone else concur? Or, can I get rid of the EGR system (no emissions testing here) all together and still run on 87 octane gas?

11-03-2003, 11:02 PM	#2
Russell Professional Grade Join Date: May 2003 Location: Fort McMurray, Alberta Posts: 7,915	I don't think that your vac advance is suppost to let it all out... One way to check if it is working is to hook up a timing light and have someone rev the engine while you time it, you should see the timing mark moving off to the left while you accelerate the engine... I took the EGR unit off my truck, all it does is make it run a little worse for the first ten minutes or so in cold weather... I would suggest leaving it in if you can... __________________ 1995 Chevrolet 2 Door Tahoe (6.6L LBZ Duramax / ZF6 / NP241 with 1 ton solid axle swap) Last edited by Russell; 11-03-2003 at 11:04 PM.

11-04-2003, 06:19 AM	#3
bigd65 Registered User Join Date: Mar 2000 Location: Clute, TX. Posts: 1,935	if eather of them loose the vacuum load, they are bad and have cracked diagfram's (wow, i miss spelled that) as far as the EGR and if you can run without it. if i'm not mistaken and from speakin from experience. if you keep your old manifold you will need to keep the EGR to be able to run on 87 octane,because of the exhaust crossover under the intake. now if you change to an intake, like the AIRGAP's, they dont have the exhaust crossover under the intake, therefore no EGR. without the crossover under the intake, it keeps the intake cooler, therefore a denser fuel charge and can still run 87 octane __________________ 2004 Silverado Crewcab 1972 Chevy Monte Carlo 2017 Chevy Tahoe

11-04-2003, 11:30 AM	#4
swervin ervin You get what you pay for Join Date: Dec 1999 Location: Cherryville, NC Posts: 4,798	Check the accellerator pump in the carb. With the engine off and warm, make sure you are getting a steady stream of gas in each primary when you slowly open the throttle by hand. Oh, and, welcome to the forum. __________________ Mike 1985 Chevy C-10

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