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post #1 of (permalink) Old 08-02-2000, 04:37 AM Thread Starter
 
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EGR valve question

OK, this may be a dumb question but I figure it's easier to ask here than try to hunt down the info in my Haynes manual. I just got a new Performer intake manifold with the EGR provision, as well as a new set of intake manifold gaskets for when I install it. The engine is a federal emission equipped GM crate 350.

<font color=red>The question is, are there supposed to be holes in the gasket for the ports from the EGR valve to the head?</font color=red> Seems like there should be, but nowhere in the documentation for the gaskets or the intake does it mention modifying the gasket. I'm sure that this will be obvious when I actually remove the current intake and look at the head, but I don't recall cutting holes in the gasket when I installed the manifold that's on there now. It's quite possible that my EGR is inoperative now if the gasket needed holes cut in it.

<font color=red>Also, my EGR valve looks like it's seen better days. Is there an easy way to test it, or should I just go ahead and replace it?</font color=red> I've heard that there were three different types used on '78 GM vehicles - positive backpressure, negative backpressure, and vaccuum operated. I assume that mine is of the vaccuum variety, since there is a vaccuum hose running to it from a little doohicky screwed into the water passage in the front of the engine. A vaccuum hose runs from this doohicky to the carb. I assume that the doohicky in question is meant to control the vaccuum applied to the EGR depending on the temperature of the engine.

Sorry for the dumb question, but this is the first engine I've ever torn into that is not smog exempt. Thanks for any help.

<font color=green>Evan</font color=green>[img]/wwwthreads_images/icons/crazy.gif[/img]

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post #2 of (permalink) Old 08-02-2000, 04:45 PM
muddfred
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Re: EGR valve question

Yes, there are supposed to be holes in the intake gaskets for the exhaust to reach the valve. The vacuum hose to the carb is what opens the EGR valve. A replacement valve can be purchased at most auto parts dealers. They usually are "one fits all" with inserts to restrict flow. The instructions tell you which insert to use based on the number on the old EGR valve. You could just block up the EGR valve hole and run without it (illegal), unless you have emission checks. If you don't use the EGR use some brass shim stock to cover the holes under the intake gaskets to keep them from burning and letting exhaust go through the intake. This will keep the intake cooler.

post #3 of (permalink) Old 08-02-2000, 07:04 PM
Zooman
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Re: EGR valve question

What does the egr valve do? When I go to put my eldebrock carb on I was going to use a performer intake the did not require an egr. The guy at the shop told me for an older truck it would not be nessesary.
Any ideas?

Zooman

[img]/wwwthreads_images/icons/crazy.gif[/img]<font color=blue>78 Chevy 3/4 in the rough</font color=blue>
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post #4 of (permalink) Old 08-02-2000, 09:27 PM Thread Starter
 
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Re: EGR valve question

Yeah, but I'm in CA, and we still have emissions testing for '73 and later vehicles[img]/wwwthreads_images/icons/mad.gif[/img]. EGR is Exhaust Gas Recirculation. It routes a small amount of exhaust back into the incoming air/fuel mixture to cut down on NOx emissions.

<font color=green>Evan</font color=green>[img]/wwwthreads_images/icons/crazy.gif[/img]

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