this post was submitted on 13 Oct 2025
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Mechanic Advice

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90's EGR Systems (lemmy.world)
submitted 4 months ago by Fuckfuckmyfuckingass@lemmy.world to c/mechanicadvice@lemmy.world
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Anybody know anything about 90's vacuum controlled EGR systems? I've got one of those goofy little Japanese import trucks, and finding info about how it's supposed to work is a nightmare.

There's a pretty good vacuum leak out of the top of the vacuum amplifier/signal doodad. Kinda UFO shaped deal between the vacuum advance, intake manifold and the canister.

Any ideas on diagnosis, or ways I can figure out what's doing what would be helpful.

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[–] sramder@lemmy.world 3 points 4 months ago (1 children)

Replace parts until it works? That shit is black magic, the one in my 90’s prelude required a wax plug to melt that then allowed vacuum to operate a valve, this valve then allowed some exhaust gas into the plenum on top of the block.

What you need is the Factory Service Manual, should be roughly the same size as a 90’s phone book and was a requirement for vehicles sold in the US.

[–] Fuckfuckmyfuckingass@lemmy.world 2 points 4 months ago (1 children)

A wax plug is truly insane. Parts for the emission system are pretty slim pickings, mostly just used off eBay. I think my bigger problem is the carb needs a rebuild something fierce. I have the carb kit and the time now so I should be able to tackle that soon. The fuel air mix screw has a little rubber washer in it that is pretty much gone so that can't be helping any.

[–] sramder@lemmy.world 2 points 4 months ago

Pure Rube Goldberg… today it would be solenoids, temp sensors and the ECU powered up 24/7, which I guess is the advantage.

It also made a random robot-farting noise about 8 hours after cooling down which I believe was the evap purge canister venting. Gave me the heebie-jeebies a few times when I was out late at night, smoking a cigarette.