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94 FWB, 93 SDV, 94 FWB (sold), 90 Brougham (sold)
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I'll be purchasing a hand vacuum pump this weekend. I can't afford not to have one any longer. I want to verify some info first. A. When the engine is running, I should be able to push up on the EGR valve and have the engine stutter and run very poorly and almost die. This is common sense, because of the increase in exhuast gas in the intake charge. So if I push up on the valve and nothing happens, this means the EGR valve itself is clogged or broken, or the passages in the intake are completely clogged. Is this correct? B. An engine running without EGR will inherently run hotter because of the loss of the inert exhaust gases cooling the intake charge. However, a knock sensor will retard timing as seen fit to end detonation. Correct? If an EGR valve is clogged or stuck, is it worth the time to soak it in a bath of solvent, or buy a new one?

Brian
 

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94 Fleetwood Brougham
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7,534 Posts
Brian,

Olds V8's (and a lot of others after 1979 or so) had POSITIVE backpressure EGR valves. My LT1 has a NEGATIVE backpressure EGR, first one I have seen in years. You have to determine the type to know how to test it. Ported are rare. The new cars all have linear. The 90's cars often had digital, but only on Port EFI cars. Mainly Buick designed engines.

The Positive types need to be revved up enough that backpressure is high enough to close the tiny valve in the EGR Valve to allow it to turn on. No amount of vacuum will activate it until it has backpressure. A clue, is it won't HOLD vacuum until it gets backpressure either. If you remove it, you will see the valve opening in the bottom of the pintle.

The negative backpress types I think will hold vacuum ok, so they are easily tested. Positives are harder to test. GM FSM shows how to though. I think you have to rev it up or load it up to get pressure enough.

I am not a fan of EGR, I feel a carefully selected cam like used in the Warrior Pontiac can accomplish the same thing. VERY careful, fast ramps (roller) are key. The overlap will start to cool the charge enough to keep combustion temps from getting too high, even with high compression. The Warrior was a 455 Pontiac with 11:1 compression, ran on 93 octane, and passed California Emissions for the 1986 model year. (Failed visual) The guru who built it was the chief emissions inspector for the state of CA. He KNOWS emissions! No EGR, no AIR pump, and it all passed. BUT, a technical fail as a 1968 Firebird didn't come with those "emissions" devices and carb. It even had a Holley carb! Properly set up that is.

Tom
 
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