AMC Eagle Den Forum
The Mighty 258 => The Engine => Topic started by: IRON HORSE on August 18, 2014, 12:16:17 AM
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Greetings,
For several years I was having problems with oil fouled air filters, and a lot of oil in the air cleaner assy. Well today I found the cause, it was a bad "trap door vacuum motor" as they call it. If the diaphragm in this vacuum motor goes bad the trap door stays closed. The trap door seals so well that the engine pulls air into the air cleaner assy. from any where it can get it. The PCV "air in" hose becomes an air out hose through which oil is pulled into the breather and fouls the air filter. I just rigged the trap door to stay open all the time, car runs better now too. I can't believe it took me so long to see it. Anyway thought I'd pass it on in case anyone else is having the same problem.
Regards, IRON HORSE :o
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Wow! Where is this vacuum valve located? Do you have more details?
Were you using a lot of oil? Blowby?
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I think he's talking about the door in the neck of the air filter housing. There is a vacuum line that runs to a diaphragm assembly on the neck that actuates a door. If it is malfunctioning, you are severely restricting airflow.
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Hello,
Draekon got it right .. If you remove the air cleaner cover ( where the filter is ) and look into the hole which the air flows into the breather .. you'll see the trap door closed if the engine is off. The trap door will be open if the engine is running, if the vacuum motor is working.
Does anyone know the reason why this was designed to close so completely ?? Then open right up when the engine starts ?? Maybe to keep the mice out if it sets for a long time ..
IRON HORSE :o
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It should work off of temperature When the engine is cold it should be closed and draw are through the stand pipe from the exhaust. after warm up it will open and pull are from the snorkel.
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Hello,
Draekon got it right .. If you remove the air cleaner cover ( where the filter is ) and look into the hole which the air flows into the breather .. you'll see the trap door closed if the engine is off. The trap door will be open if the engine is running, if the vacuum motor is working.
Does anyone know the reason why this was designed to close so completely ?? Then open right up when the engine starts ?? Maybe to keep the mice out if it sets for a long time ..
IRON HORSE :o
It was designed for pollution control. As soon as the engine is turned off, all the remaining gasses and vapors are trapped in the air cleaned and are supposed to be collected by the charcoal canister. This is how some of the last of the carbureted cars in the late 80s still passed EPA standards before fuel injection was required.
There are actually two vacuum operated doors on the air cleaner. The one rmick mentioned is right above the stand pipe, and won't completely block off air flow. The pollution control one is closer to the center and will close all the way when there is no vacuum.
That still doesn't explain the oil in the air cleaner though. I suspect blow-by. My engine starting getting super oily in the air cleaner that it would completely saturate the felt wad of the breather everyday. I rebuilt my engine and haven't had any trace of oil on the breather since.
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Hi All,
TLC87Eagle .. trapping the vapors as a pollution control was something I didn't know, thanks for that info. I never expected the failure mode to be fully closed so I never checked the trap door, I assumed it was open. Runs a lot better now, and gets right up to 85 without any problem, should notice some mpg improvement also. I hope it's not blow-by, engine does have 269,000 on it, no smoke out the tailpipe, but leaks around the valve cover. I installed a new air filter, so I'll see if the oil soaking persists, I'll give it a month or so and post what I found. Thanks again for that info ... good stuff.
Soon, IRON HORSE :o
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I've also noticed the early Amc 4.0s will suck air from the exhaust manifold when cold, and use the same flap. It is also interesting to see that the 4.0 also has issues with oil getting into the air cleaner.
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Hello, Well it' been about a month .. noticed a huge inprovement in MPG, which is understandable. As far as the oil in the breather, there is still some oil getting to the filter but not like it was. Suppose what I see now is from blowby and I'll just have to live with that. The rust is what will bring this Eagle down, I figure at most I'll get another year out of 'er. I bought it in late 1990's, put on the road in 2000 and been drivin' it ever since; I'll miss this old bird when it's gone. Later, iron horse :o but I have six more to choose my next one from ... http://i351.photobucket.com/albums/q442/IRONHOURSE/IM001809.jpg[/IMG][/URL]
http://i351.photobucket.com/albums/q442/IRONHOURSE/IM001807.jpg[/IMG][/URL]
http://i351.photobucket.com/albums/q442/IRONHOURSE/IM001804.jpg[/IMG][/URL]
http://i351.photobucket.com/albums/q442/IRONHOURSE/IM001813.jpg[/IMG][/URL]
http://i351.photobucket.com/albums/q442/IRONHOURSE/IM001720.jpg[/IMG][/URL]
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You're crazy. I love it. :3
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I run a hose from the valve cover into a cannister, then to the air cleaner to catch the nasty stuff.
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Love the pics iron horse
Seems like owning an eagle turns us into hoarders, I feel better knowing I'm not the only one
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Thanks carnuck for the info :) .. I am going to make a canister to catch the oil. :o or I could route it into the frame to keep it from rusting !! just kidding.
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thanks again
moved picts that were here to "your eagles"
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Hello everyone, I put my blow-by to good use ... here's what I ended up doing ... I removed the PCV and attached a hose .. then I removed the hose that ran to the breather ( from the breather ). Now I have two hoses that blow oil vapor from blow by or what ever the cause. I ran one hose into the left and one to the right front frame areas where they tend to rust. At first I just laughed at the idea but finally thought .. why not .. recently took this Eagle off the road .. but it actually showed signs of getting wet with oil, it was working !!! Disclaimer: Probably not EPA approved :-X Iron Horse :o
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Since you removed the PCV valve, make sure you have a filter on those lines, because they will also have a vacuum on them at certain times and will suck dirt into your engine.
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It seems my vacuum motor does the reverse. With the car not running. the flap is down covering the hole that leads to the exhaust and when the car is running and at temperature, the flap moves up and closes off the snorkel. Could it be my car is not achieving operating temp? I have a big aluminum radiator and the temp gauge needle never gets to half way up in the green zone.
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The heat stove diverter flap will operate and pull air in from around the exhaust manifold as long as the TAC temperature sensor calls for warmer air. The whole setup works based on the heat of the exhaust manifold and the radiator type won't affect it. You can test if its working by putting a heat gun or blow dryer on the sensor.