Hi dunno if I’m in right place but I have Range Rover sport 4.2 v8 sc and I’m having trouble She’s gone into reduced proomance and getting missfire and I can hear a hissing noise witch sounds like the drivers side of the engine I have just bought new plugs and plan to fit them to moro but struggling with the hissing noise is it ment to be there or not the symptoms are it won’t really rev past 3k and u can only put ur foot on peddle light witch will gradually pick up speed if u put it on to much the car looses power and same with when going up hills it will lose power 😔

You need to find the air leak and sort it, squirting a bit of easy start around the intake joints will tell you if its drawing air (the engine speed will increase). You obviously don't want to squirt lots as it's flammable and your exhaust manifolds can ignite it (so pro tip is to test when the engine is cold).

Check the oil filler cap is tight as well.

Ok thanks I will try this to night so shouldn’t be getting a hissing noise from engine

Nope, fingers crossed it’s something simple. Start at the air filter and work your way back to the throttle body. If you have a leak after the throttle body repairs start to get expensive

Ok thanks I’ll give it try to night hope not lol

Just been looking and the picture attached the pvc long pipe wat goes to back engine if I undo it on the valve and start the car put my thumb over it the hissing leak sound stops and when I re attach it u can hear the hissing again

Just been reading and seems the jag engines have slight hissing due to the pipe or something and it’s normal I sprayed carb cleaner all over and no change in engine gonna fit new spark plugs to moro and hope for the best lol

You’ve found your leak then, it’s probably the pipe that’s split or a damaged ‘o’ ring. Check the pipe for leaks, if there aren’t any then it might be worth replacing the pcv valve.

Update on the car changed plugs and noticed the coil pack on cylinder 2 been changed and isn’t Denso 1 so I Range car place up and couldn’t get a Denso 1 so bought another witch was suited to the car fitted it and still got the same problem reduced profirmance and car still like bucking and looses power mainly at 3k revs or on hills etc would u go for injectors next seemes like fuel problem I think as the way it doesn’t want to go under load but will rev up when in park 😔

It’s down to the air leak, there should be no hissing from the engine.

Get the fault codes read and it will point you in the right direction as I highly doubt that it’s an injector that’s not right, but rather than pulling the injector (pretty big job) try putting a can of BG44 fuel additive in, if it improves then it may well be a failing injector.

When adding the BG44 I usually wait till the fuel warning light comes on, put in the additive and £15/£20 of fuel. Run it till the fuel light comes on before filling it again.

The hissing noise will stop when I put my hand over the pcv valve pipe but I think it’s just the noise it makes with the plastic pipe and it’s tricking my ears Otherwise the hissing near were number 2 cylinder is but not sure

Is there any 1 close to Wigan with the 4.2v8 supercharged engine we’re can listen there engine

Block the pipe with some electical tape and go for a drive. See if that fixes it.

Take it the pipe off the pcv and block the long pipe

Just disconnected it and blocked the long pipe had no change I reset the engine light so went off and went round corner and reduced proformance came back on when trying to take it over 3k revs think might be fuel issue as seems to Langton 1s it gets to 3k like it’s looking for fuel