Hissing noise from engine

[Devil Doc]

A few weeks ago, I was involved in a minor vehicle accident in my beloved XJ. Most importantly everyone was ok and both vehicle had relatively minor body damage. My jeep still drives straight and I haven't noticed any change in ride quality. My temperature and oil pressure guages are normal and there is no change in performance or idle.

BUT...I noticed immediately afterwards, I have a hissing noise coming from what sounds like around the fuel injector rod or on the right side of the valve cover, but its that general area from the front of the valve cover to the rear. I'm wondering if it might be a small crack in the manifold? Would it make that kind of sound without having any performance issues? The impact was on the side of my jeep and it spun my jeep horizantal in front of the truck that hit me and I slide sideways at about 40mph before stopping. Fortunately the nerf bar I reallly believe prevented me from flipping because it got caught under the dudes front bumper. And it also prevented any major body damage. But the amount of force it took to bend the crap outta those bars had to be pretty significant so I'm hoping it didn't crack or bend something in the engine.

[cantab27]

have you got pics.....any new fluids leaking.....

[4.3LXJ]

Sounds like it might be a vacuum leak. Check your hoses. Idle speed up by any chance?

[XJEric]

Id imagine if it was a vacuum leak, and as loud as you say, I'd think you'd notice some engine problems, as even small leaks can make it run rough. Check all your vacuum lines though I guess, perhaps one fell off? I changed my air filter, and one of the two vacuum lines that run to the back of the box fell off, and that was very loud.

Maybe it impact caused the exhaust manifold to crack? I had a loose bolt on mine that caused it to leak, made a noticeable noise, but I can't recall if it was a hiss.

[4.3LXJ]

If you only have a very small leak, less than the idle air controller passes for idle, it will compensate by passing less air and the engine will run normally

[bigjim350]

It does sound like a vacuum leak. Here is a good way to check. Try your best to narrow down where the sound is coming from and start spraying wd40 or starting fluid in that area. When the fluid is sucked into the leak your engine will increase in RPM if it is a vacuum leak. This will also help narrow down the area.

[Devil Doc]

Thanks for the responses, you guys are awesome. As an Army Medic, I use to say if it bleeds or breaths I can fix it, but I don't know shit about cars. And now I've bought the mechanics book for my jeep and have traded blood on my hands for oil. I can live with that!

I checked all my hoses today and nothing seems out of the ordinary. I crawled around a bit under the hood and tried to locate exactly where the sound was coming from. I highlighted the area in red on the picture I've included. It's not super loud but it's audible over the rest of the engine and fan noise. Perhaps tomorrow I'll take a short video clip if you guys think it'll help?

http://i218.photobucket.com/albums/cc257/DjCounterpoint/2yvnode.jpg

[4.3LXJ]

Yo have highlighted the most likely spot. Plenty of possibilities there

[steph74]

check that the exhaust/intake manifold is till tight.... mine was the last bolt closer to the firewall was somewhat missing... the hissing stopped once I replaced it.

And of course as everybody says... check the vacuum lines

[Mudderoy]

A few weeks ago, I was involved in a minor vehicle accident in my beloved XJ. Most importantly everyone was ok and both vehicle had relatively minor body damage. My jeep still drives straight and I haven't noticed any change in ride quality. My temperature and oil pressure guages are normal and there is no change in performance or idle.

BUT...I noticed immediately afterwards, I have a hissing noise coming from what sounds like around the fuel injector rod or on the right side of the valve cover, but its that general area from the front of the valve cover to the rear. I'm wondering if it might be a small crack in the manifold? Would it make that kind of sound without having any performance issues? The impact was on the side of my jeep and it spun my jeep horizantal in front of the truck that hit me and I slide sideways at about 40mph before stopping. Fortunately the nerf bar I reallly believe prevented me from flipping because it got caught under the dudes front bumper. And it also prevented any major body damage. But the amount of force it took to bend the crap outta those bars had to be pretty significant so I'm hoping it didn't crack or bend something in the engine.

Have you inspected your exhaust system carefully? From collector all the way back. Also you can use a 3 foot long piece of vacuum hose and place one end up to your ear the other end as a way to pinpoint exactly where the hissing is coming from.

[LizardRunner]

since your a medic, you probably have a stethascope, that will help you locate the leak. I have one and it has come in handy many times. I also have mechanics model and it really helps with locating pesky internal engine noises.

[Devil Doc]

since your a medic, you probably have a stethascope, that will help you locate the leak. I have one and it has come in handy many times. I also have mechanics model and it really helps with locating pesky internal engine noises.

Hey, that was a really great idea!!! I used one of my old stethoscopes and narrowed it down to the near side intake manifold. And once I could hear where it started getting really loud, I put my finger there and it would stop and the idle would adjust a little. So now I'm wondering if I'll need to replace the whole gasket or if I can try to just torque down the bolts a little (maybe they came loose in the acident)?

[4.3LXJ]

It might be just coincidence. Torque them down and see what happens.