Low Vacuum Reading but running normal.
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5th Wheeling
Joined: Aug 2019
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Low Vacuum Reading but running normal.
Hello all,
01 F250 with around 371,000. Not sure if mileage is correct.
I have been trying and trying to find a vacuum leak since I got this pickup 2 years ago. I have checked the PCV hose and found one line unhooked and fixed it. It seems to sputter a little at idle,runs great otherwise, but I still hear a hissing noise and it seems to run rich by smell, mileage, and the amount of condensation coming from the exhaust. It reads about 9.9 inches at idle. Am I chasing a ghost?
01 F250 with around 371,000. Not sure if mileage is correct.
I have been trying and trying to find a vacuum leak since I got this pickup 2 years ago. I have checked the PCV hose and found one line unhooked and fixed it. It seems to sputter a little at idle,runs great otherwise, but I still hear a hissing noise and it seems to run rich by smell, mileage, and the amount of condensation coming from the exhaust. It reads about 9.9 inches at idle. Am I chasing a ghost?
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5th Wheeling
Joined: Aug 2019
Posts: 39
Likes: 1
Must be thinking of a different forum...
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5th Wheeling
Joined: Aug 2019
Posts: 39
Likes: 1
The PCV valve rattles, and the lines all look solid. The gauge is fairly steady. It's just a cheap digital gauge though so take that for what it's worth..it holds steady around 9.8-10.1 in/hg. There is a hissing noise around the throttle body area, almost sounds like a carburetor engine if that makes any sense.
FTE Leadership Emeritus
Joined: Jul 2002
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From: Long Island USA
My '01 made that same sucking noise - brand-new. 
Remove and plug every potential vacuum leak - including the brake booster. If there's no change, you either have a hell of an intake leak (or throttle body gasket) or just a tired engine.
Did you do a compression check yet?
Remove and plug every potential vacuum leak - including the brake booster. If there's no change, you either have a hell of an intake leak (or throttle body gasket) or just a tired engine.
Did you do a compression check yet?
Thread Starter
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5th Wheeling
Joined: Aug 2019
Posts: 39
Likes: 1
My '01 made that same sucking noise - brand-new.
Remove and plug every potential vacuum leak - including the brake booster. If there's no change, you either have a hell of an intake leak (or throttle body gasket) or just a tired engine.
Did you do a compression check yet?
Remove and plug every potential vacuum leak - including the brake booster. If there's no change, you either have a hell of an intake leak (or throttle body gasket) or just a tired engine.
Did you do a compression check yet?
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FTE Leadership Emeritus
Joined: Jul 2002
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From: Long Island USA
Maybe the IAC is stuck open. Pinch it's hose and see if the vacuum goes up.
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5th Wheeling
Joined: Aug 2019
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But, this does remind me that I had to clean the IAC when I got the pickup. It's a good place to start looking.
FTE Leadership Emeritus
Joined: Jul 2002
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From: Long Island USA
Don't quote me on this, but I think the PCM will try it's damnedest to get the idle down, even to the point of pulling the timing. Which would explain the low vacuum.
I seem to remember my '01 would pull around 14 or 15 at idle. And yes, I actually did install a vacuum gauge
I seem to remember my '01 would pull around 14 or 15 at idle. And yes, I actually did install a vacuum gauge
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5th Wheeling
Joined: Aug 2019
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Hm well that would make sense, since I've suspected the timing being a little off before...I will go get an actual vacuum gauge first chance I get and see how accurate my little digital one is, then go from there. If its just an IAC then that's not too big of a fix!
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5th Wheeling
Joined: Aug 2019
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Okay, so I went out and pinched the IAC hose, and the vacuum went up to 10.5ish on my little OBD reader.
If I completely take the hose off, the vacuum went up to 15ish and of course the engine went crazy, but does any of this make any sense?
If I completely take the hose off, the vacuum went up to 15ish and of course the engine went crazy, but does any of this make any sense?
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