Hello,

I have this loud hissing noise coming from the engine bay the noise originally came and went now it is there all the time not troughing any codes and seems to only minimal power loss I have attached a recording does anybody have any input on this.

Head gasket ?
Intake Gasket ?
Cam lob closed exhaust valve ?

Also if i pull the #7 spark plug wire the noise goes away

 

Would suspect valley pan gasket. Might be a good time to do a compression check. Can you narrow it down by listening "thru" a stick or rod pressed against the engine and to one of your ears?

 

You are too lazy to look so we get to guess. Get you butt under the hood and listen till you find it, hell we don't even know what color your truck is and you want us to tell you what is wrong with it.
After you go do the work, find the problem, then get back to us if you need to know what to do next. By the way, how mechanical are you, will you be doing the repairs, if not, just go take it to a shop and have them find/fix the problem.

 

2000 discovery 4.0
This lazy Guy has been under the hood and cannot locate the problem hence why I have come here looking for help I have done a compression check of all the cylinders theye were all within 20 psi of each other and sprayed Carb cleaner all around the intake looking for for a possible vacuum leak I have come up with nothing I was so hoping that possibly someone at some point may have had a similar noise from the disco and could provide some insight..

 

Well, if it is a "hiss" like air coming out under pressure, as opposed to a "whistle" of a vacuum leak, perhaps a spray bottle of soapy water. Air coming out will make bubbles, just like on a leaky tire. But there is not much under a Disco hood that makes a constant air pressure. I suggested the valley pan, because a lot of it is hidden from easy visual examination. The old trick of listening via a broom handle might be modified for this - what about listening through a length of rubber hose, while you move the hose around suspect areas, snake in over the valley pan, etc.? Just something to block down the extra noise in the engine bay. Maybe even try a smaller diameter hose, and put it under one side of a pair of hearing protectors (OSHA earmuffs). There is no shame in hearing loss, whether it be from cannon fire, rock music, or just driving for years with the window down. I can't hear half of what she-who-must-be-obeyed lists on the daily duty assignment.....

 

It can also be an exhaust leak from a blown head gasket, if so you need to catch it before it cuts a groove in either the block or head.

 

Sounds like and exhaust leak to me. Hard to say from just hearing a recording but, I have heard of the manifold bolts loosening off before and making a sort of ticking noise. Could be a possibility but, may be a head gasket leak. Better track it down asap! Don't let it go too long, it may cost you an engine!

 

I have vehicle parked for now, tonight I pulled the exhaust manifolds in hopes of getting lucky wow that was a pain in the rear three of the bottom studs were so rounded the 12mm did nothing for it luckily I was able to hammer an 11mm on em apply some heat and get them out.
Its hard to say just by looking at the old gaskets as they all looked fairly rough so new bolts and gaskets on order..

 

Make sure you look at the manifold really close too, some were recalled because of cracking. I'm not sure about yours but you could look it up online. Just remember that if you get the new exhaust gaskets in there and it still does this and you don't see any cracks in the manifold it really may be a head gasket, if so it's going to need replacing VERY soon! For your sake I hope it turns out to be just the manifold gaskets! Good Luck!