found that the inside was covered in soot and smelled like gas.... we were told this was caused by mechanical timing problems. True??? OR is it normal. Whats the best way to get all the carbon/soot out anyway?>?
How can I stop it from getting BACK in there???

Thanks,
Tony

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Tony

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Whoever told you that is an idiot

The soot is from the exhaust gases that pass trough it. They come from the EGR ports right at the entrance in the plenum. I guess the only way to keep that from coming back is to disable EGR. Now gas shouldnt be in there. I guess the only way it could have gotten in there is trough the EGR ports or from the gas tank vapor recovery canister. Maybe you can try changing the filter on that. I'd all this is pretty much normal. I've looked at a lot of plenums and they were all dirty inside, including the runners. Now, mine's clean because I don't run EGR anymore, but I could care less if it's clean or not. That's my 2 cents on this

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I believe this is caused by the EGR, which cycles exhaust gases back into the intake to facilitate full burn of the fuel. You will inevitably get some buildup of soot, but it shouldn't be excessive if the EGR is functioning properly.

 

As far as getting the soot out... go buy a couple of cans of carburator cleaner and spray it all in there. That will clean it pretty damn good.

 

The smell of gas in the plenum could be an indicator of the engine running rich, as there would still be fuel in the exhaust gases that get routed back through the plenum. I would expect some odor to exist even when the car is running properly tuned.

 

Carb cleaner or access to a parts washer will clean it up.

 

...and in three months it will all be back again. No air filter is 100% effective in trapping all particles and moisture. Once the moisture hits the hot walls of the plenum, the little spec of dust that the water droplet was encapsulating will bond to the wall when the water is evaporated. A few million more specs of dust glued to the walls of the plenum, along with a good dosage of evaporated fuel and oil vapors every time you shut off the warm engine, and the dust and dirt will be baked on really well.

The buildup isn't even a problem unless it is about 1/8" thick or more.

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Vader
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The joys of a tuned intake...

Unless you have a leaky valve, or one of the above maladies, you are experiencing the normal reversion from a tuned intake setup. There is enough shock wave returning up the intake to send some fuel vapor flying the wrong way, and thats where the gas smell is coming from. I have seen this on every TPI I have had apart, some to a lesser extent than others probably due to valve sealing issues. The intake I cut to death with a mill no longer has this problem. I cleaned the runners and plenum before I swapped the intake on, and 4000 miles later there was no trace of fuel, and very slight buildup from the EGR. The base however still had some fuel and more buildup than the rest of the system, so its stopping there rather than heading back up the runners and into the plenum.

Generally its more of an annoyance than a problem. Just keep the TB and IAC area clean, and it will be fine.

 

thanks guys u put my worries to rest.....the buildup wasn't really that bad it was the smell of gas that worried me but its all good now...did some mild porting(Thanks Vader great write up on that) and clean it all up

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Tony

 

Man, all you EGR soot haters, lol. Don't forget that the PCV system use the EGR passages to dispers, so on top of what vader and max mentioned, there is also crankcase oil vapors constantly being run through there, which i imagine is a better glue than any of the aforementioned funks.
...ed

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