Can You Help Me?
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Joined: Jul 2015
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Can You Help Me?
I have a 1994 4.9L F150 and I have two problems. 1) it idles rough, however runs fine when in drive. 2) I have a vaccum leak like sound when I drive past 40 or 50 mph. It's more hear able going up hill. Before the issue, the truck going up hill sounded somewhat like a diesel, just giving an idea, and now it sounds like the sound someone makes when they're sucking on an empty cup with a straw. Those two issues are driving me insane and it's been like that for a couple of months now. So, I'd happy to hear any solutions or ideas from whomever can help with these problems and if I missed a detail I'd be glad to inform some more.
New User
Joined: Mar 2015
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Have the vacuum lines been checked? Vacuum likes love to crack and cause leaks. My 88 F150 has had pretty much every line replaced on it. Some are just spliced in where a hard line cracked, but the owned before me replaced all the rest end to end as a precaution.
Vacuum leaks will cause rough idle issues. I wold think you have a pretty good leak if you are hearing it that clearly when driving. I would suggest inspecting the lines, along with all the intake tubing. Also look around the manifold for any signs of a bad gasket. Usually intake gasket leaks lead to higher idle as the computer tries to compensate for the extra air though.
Vacuum leaks will cause rough idle issues. I wold think you have a pretty good leak if you are hearing it that clearly when driving. I would suggest inspecting the lines, along with all the intake tubing. Also look around the manifold for any signs of a bad gasket. Usually intake gasket leaks lead to higher idle as the computer tries to compensate for the extra air though.
Postmaster
Joined: Mar 2005
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From: Earth
You can check for vacuum leaks with a cigar. Pull the brake booster hose and clean off the end so you can wrap your lips around it. Light the cigar and start puffing, then blow the smoke into the booster hose. It takes a few drags to get the intake, etc. full of smoke but eventually you'll be able to see smoke coming from anywhere it's leaking. The cigar takes the place of a ~$1,500 smoke generating tools some shops have to do the same thing.
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