what is pluged
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Senior User
Joined: Dec 2007
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what is pluged
i have come to realise that this is not normall the vacume line on top of the air breather on a 83-f100 make the engine run better when it is disconected! the engine speeds up gust a bit but smoothens out and gets way more power and sounds totally diffrent i put it back on i know i shouldnt run it wothout/ but why does it run better with it off? there is loots of vacume going trough it truck always runs good gas millage suck though
sorry for long qeustion
sorry for long qeustion
MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
Normally, on a healthy engine, combustion fumes escape past the piston rings and enter the combustion chamber. They are then directed back into the intake manifold through the PCV valve. A breather filter on the other end accepts fresh air into the crank case, through the breather hose.
If you're talking about the breather hose, then your situation is due to excessive blow by. On old engines, there is so much blow-by that the PCV system is in effect swamped by blow-by, and the crankcase fills with more fumes than the system can suck out. So it tries to escape any way it can - even out the breather hose. This is bad because the breather hose is supposed to take in fresh air, not dump combustion fumes out. What happens next, is the breather filter starts fouling, and eventually the air filter starts fowling. Another term is "throwing oil." The engine begins to bog down due to excessive crankcase pressure.
So, sometimes people will disconnect this hose to let the fumes escape, and it will run better because this helps release crankcase pressure and the engine bogs down less. Normally, you're not supposed to disconnect this hose because it needs a filter on it. But, if your engine's blow-by is so bad that it just keeps dumping fumes and fowling breathers, then your PCV isn't really helping anymore and it really doesn't matter if you leave it connected or not. My '77 LTD has a 351W and is this way. The blowby is so bad that it comes out the breather hose and the PCV hose at the same time. I just ran a 5/8" heater hose from the valve cover grommet down to the ground to dump the fumes.
This is all assuming you are talking about the breather hose, because this is the only case that would make sense. If you're talking about an actual vacuum hose, then it's not supposed to run better with it disconnected. Vacuum leaks are bad. If a vacuum leak makes your engine run better, you have a problem. My guess would be your idle is too rich, which would also contribute to the poor gas mileage you mentioned. You need to clarify which hose you are talking about.
Hope that helps, sorry but a long question needs a long answer.
If you're talking about the breather hose, then your situation is due to excessive blow by. On old engines, there is so much blow-by that the PCV system is in effect swamped by blow-by, and the crankcase fills with more fumes than the system can suck out. So it tries to escape any way it can - even out the breather hose. This is bad because the breather hose is supposed to take in fresh air, not dump combustion fumes out. What happens next, is the breather filter starts fouling, and eventually the air filter starts fowling. Another term is "throwing oil." The engine begins to bog down due to excessive crankcase pressure.
So, sometimes people will disconnect this hose to let the fumes escape, and it will run better because this helps release crankcase pressure and the engine bogs down less. Normally, you're not supposed to disconnect this hose because it needs a filter on it. But, if your engine's blow-by is so bad that it just keeps dumping fumes and fowling breathers, then your PCV isn't really helping anymore and it really doesn't matter if you leave it connected or not. My '77 LTD has a 351W and is this way. The blowby is so bad that it comes out the breather hose and the PCV hose at the same time. I just ran a 5/8" heater hose from the valve cover grommet down to the ground to dump the fumes.
This is all assuming you are talking about the breather hose, because this is the only case that would make sense. If you're talking about an actual vacuum hose, then it's not supposed to run better with it disconnected. Vacuum leaks are bad. If a vacuum leak makes your engine run better, you have a problem. My guess would be your idle is too rich, which would also contribute to the poor gas mileage you mentioned. You need to clarify which hose you are talking about.
Hope that helps, sorry but a long question needs a long answer.
Thread Starter
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Senior User
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the case around the air filter (the air breather is what i call it) has two line on the top of it with two spots to plug them into if you take the one that sucks air off the engine it idles up but has a better top end the blow by isnt bad the hose at the front of the valve cover on the oil cap has be ran to the growned because of it but it took about a month and 2week for oil two show up in the air breather case thats why its disconected
Cargo Master
Joined: Apr 2003
Posts: 3,476
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From: Frequently frozen MN
If I'm reading this right you're disconnecting 2 lines one goes to the underside of your air filter case. This is the one that helps your power. The other one is to your PCV. You disconnected the 2nd one because it squirts oil into your air filter.
I don't think these are related. Your PVC problem is probably what fmc400 said. As for the 2nd -- this is strange.
What you're describing should be the hose that causes the snorkel to switch to cold air after the engine warms up. Before that it's supposed to suck air from the hose going down by the exhaust.
I can see that you could have some kind of a restriction in your fresh air intake. In that case, you would be better if it kept sucking through the hose going down by the exhaust . If the hose to the exhaust is rotted away, then
it would work even better.
What I can't see is how you can get by with causing a vacuum leak. What happens if you pull the hose off of the air cleaner and plug the end? If it runs even better then you have a restriction in your cold air intake. If it runs worse, then you have one screwy problem.
good luck,
ford2go
I don't think these are related. Your PVC problem is probably what fmc400 said. As for the 2nd -- this is strange.
What you're describing should be the hose that causes the snorkel to switch to cold air after the engine warms up. Before that it's supposed to suck air from the hose going down by the exhaust.
I can see that you could have some kind of a restriction in your fresh air intake. In that case, you would be better if it kept sucking through the hose going down by the exhaust . If the hose to the exhaust is rotted away, then
it would work even better.
What I can't see is how you can get by with causing a vacuum leak. What happens if you pull the hose off of the air cleaner and plug the end? If it runs even better then you have a restriction in your cold air intake. If it runs worse, then you have one screwy problem.
good luck,
ford2go
MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
Okay, I understand what you're saying now. You already have the breather hose running to the ground because of blow-by (I had to do that on a car too, like I said). You're actually disconnecting a vacuum line. Your idle is going up because of a vacuum leak. Like ford2go said, that's odd. My guess is you're running too rich and the vacuum leak is leaning it out to spec.
