Hissing sound

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Dec 8, 1999 | 08:58 AM

Herby

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Hissing sound

My '90 F150 has developed this hissing sound coming from the right front of the engine (302).
I haven't had time to really investigate but it seems to be coming from the EGR area. The truck runs okay except the idle is about 100-200 rpm higher when warm. I plan to research more this weekend. Any ideas on what I should look for? The obvious culprit is vacuum. Any others.
Thanks in advance,
Herby

Dec 8, 1999 | 11:23 AM

PAUL_2

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Hissing sound

Herby ,
Sounds like you have a vacuum leak , hose and or gasket . They can be hard to locate . Thats what is causing your higher than normal idle .

Dec 8, 1999 | 04:03 PM

Kyle

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Hissing sound

You definatly have a vacuum leak. I just got one fixed in my '88 F-150. I have a 302V8 also, the leak was in the intake gasket. It was cheap to fix, and there was a very noticable improvment in power and take-off.

Kyle
'88 F-150 4X4

Dec 8, 1999 | 07:47 PM

Herby

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Hissing sound

It was a vacuum leak in the intake manifold. On the inside at the middle bolt. Is this fairly easy to fix? It's my only vehicle.
Herby

Dec 17, 1999 | 12:45 PM

Dylan Schwilk

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Hissing sound

I just had the same symptoms on my 5.0 EFI. Also some surging coasting downhill. I fixed the vacuum leak at the upper intake manifold gasket where there was about a 4-inch long leak. (1990 F250). I'm a auto novice -- this was my first non-routine under-hood repair -- and it went smoothly but did take some time what with removing the air hoses, upper radiator hose and throttle body so we could see what we were doing.

-Dylan

Dec 17, 1999 | 03:13 PM

Chuck

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Hissing sound

I know it's obvious, but I'll reiterate anyway.. make sure to label all vacuum hoses, lines, etc, so you don't hook them up incorrectly on reassembly. You may think you'll remembers where they all go, but trust me.. after 3-4 hours under the hood, you'll forget!

Chuck

Dec 21, 1999 | 03:10 PM

Herby

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Hissing sound

I got the gasket replaced with no problem. It took the better part of a Saturday because I took my time and I cleaned out the throttle body and the upper intake. It was really caked in there. I also planned to replace the valve cover gaskets but they were "glued" on pretty good and I was running out of daylight. Next time. By the way, thanks to all for the info.
Herby