vaccum leak?
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New User
Joined: Sep 2008
Posts: 5
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From: South MS
vaccum leak?
I have a 1994 f 150 5.8 auto 4 x 4. For a few months when going up a hill the ac would start blowing through the defrost vents and then after toping a hill it would go back to blowing through the dash vents. Not a big deal to me so I havent done anything about it. I figured it was a vaccum leak. Last weekend I was out and the check engine light would come on and off. When it would come on the truck would shift really hard, idle very high and run like it was running out of gas when I would press the gas petal. If the light was off everything was normal, it would only act up when the light was on. I do not have a code reader. Could these symptoms be associated with the vaccum leak?
Laughing Gas
Joined: Mar 2005
Posts: 765
Likes: 1
From: ct
my truck is the same year as yours but its an f 250 with a 351 4x4.my check engine light was on to.The book said the check engine light is an emmisons issue.it turned out to be the oxygen sensor.now my truck runs alot better.you need to have someone read the code for you thats how you will find out whats wrong.someone told me autozone reads the codes.may wanna check that out and its free.
Lead Driver
Joined: Aug 2006
Posts: 5,670
Likes: 13
From: Sand Lake, MI
The switch to defrost is normal with little or no vacuum, defrost is the default setting to ensure it can keep the windows clear regardless of any possible engine performance issues that might arise.
Yea question is why is your engine vac so low, fairly steep and long hill to climb? Normal to an extent then.
If a small short climb or it didn't do it before on the same hill or hills then you have an issue needed corrected.
Check for vac leaks and check the engine base timing.
And yea check it for trouble codes, its gonna give you something to go on too. You can do so yourself with nothing more then a paper clip if you wish.
Ford Fuel Injection How To Run a Self-Test
Yea question is why is your engine vac so low, fairly steep and long hill to climb? Normal to an extent then.
If a small short climb or it didn't do it before on the same hill or hills then you have an issue needed corrected.
Check for vac leaks and check the engine base timing.
And yea check it for trouble codes, its gonna give you something to go on too. You can do so yourself with nothing more then a paper clip if you wish.
Ford Fuel Injection How To Run a Self-Test
Fleet Owner
Joined: Oct 2005
Posts: 20,786
Likes: 1,751
From: Kentucky
The white vacuum line running to the blend door is well known to break or be very brittle. Look near the passenger side of the engine bay on the side of the blower/evaporator case. There is also a small plastic reservoir mounted on the same case on the engine side that is known to crack. Third area to check is the metal vacuum reservoir that looks like a large coffee can. It will rust through which in turn can cause the vent problem and turning on the CEL. Pull the codes as mentioned before and inspect/repair the items I mentioned.
Fleet Owner
Joined: Oct 2005
Posts: 20,786
Likes: 1,751
From: Kentucky
Vacuum leak.....
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Senior User
Joined: Mar 2010
Posts: 137
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My 97 F250 just started blowing out of the defroster all the time now no matter how i am driving. I've checked all the vacumn lines and im at a loss. No CEL either.
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