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post #1 of (permalink) Old 01-28-2000, 02:12 PM
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EGR Problem?

My problem has to do with a 1978 Ford Bronco with a 400 V8 and it has me stumped. The truck has a new fuel tank, new fuel pump, fuel lines have been flushed out and I've had two different rebuilt carburetors on the engine. The engine has around 65000 miles on it, and was originally balanced and blue printed by a reputable shop. I bought the engine from my uncle when it had about 55000 miles on it, my uncle being real picky about keeping a new motor in his trucks. It has had lower than normal vacuum since I installed it last April, 8 to 9 inches. The EGR has a new vacuum switch that opens at 160 degrees. The EGR valve does hold vacuum, and opens with no restrictions in the exhaust gas flow. A week ago it blew out the power valve in the carb, and I decided to yank the entire intake manifold to find out why I had low vacuum. I found a small vacuum leak between the intake and EGR spacer. I put in a new power valve, installed a spare intake and EGR/carb spacer that I had and reinstalled all the other parts. After reinstalling I got 17 inches of vacuum, and everything ran fine, until the EGR opened up, then vacuum dropped to 8 to 9 inches and the engine started surging, not a lot but enough to notice. With the EGR plugged off I get 12 inches of vacuum, but the carb will not adjust out. I had the idle adjustment cranked nearly all the way down to keep it running, and the enrichment adjustment screws have to be nearly all the way in before the engine stumbles. I am beginning to think the carb is shot. Anyone else have any ideas?

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post #2 of (permalink) Old 01-28-2000, 02:25 PM
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Re: EGR Problem?

I don't have any experience with that particular engine, but I would expect about 20 inches or so of vac at idle, assuming it doesn't have some wild cam in it. There shouldn't be any EGR at idle, EGR should only start to open up at higher RPM. As for the carb, is your idle circuit in the carb working, or are you opening the throttle plate quite a bit to get it to idle on the main power?

8-9 inches of vac at idle sounds really sick. So bad, I wonder if its correct. Good vacuum gauge? Using a true manifold vac port on intake?

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