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Hello everyone! This is my first post on this wonderfully useful site, been perusing its pages for a while now. I'm hoping someone might be able to offer some help with a seemingly unusual problem.

My 2005 2.0L 16v Megane II (F4R engine) is making an odd hissing/blowing noise similar to a very small turbo when accelerating hard or under load eg. up a hill. If I drive the car gently it doesn't make the noise at all and the car runs and idles very well. If I keep pushing the car once it begins to make the noise it will eventually misfire or skip and dramatically lose power until I release the accelerator.

I'm fairly sure it is a vacuum or inlet problem because of the misfire - sucking in excess air and making it run lean - plus it just doesn't sound like an exhaust leak to me, no ticking/tapping or inappropriate farty noises...

I checked all hoses and connections going to/from inlet manifold and couldn't find any cracks or holes so I ordered new inlet manifold gaskets - the ones between nylon upper and aluminum lower manifold sections, and the throttle body to inlet manifold gasket. When I removed the old ones they were all were pretty hard and rough looking. The area behind the join on cylinder number one had a small oil leak around it and that gasket was a little worse than the others. There was also a fair amount of oil in the inlet manifold, maybe 100mls or so.

After changing the gaskets there was a slight improvement in the noise ie. it seems to need to be pushed a little harder to make it misfire and skip. But the hissing/blowing is still there.

Next thing I replaced was the oil vapor valve, its hose and 'resonance' box that connects to the crankcase. I didn't expect them to be the problem but they were the originals and seemed a little gummed up with oil, changing them made no difference.


Given that I have checked and replaced the most obvious culprits, I am a little stuck and am now wondering about the gasket/shim between the lower inlet manifold and the block. When I first got the car the engine mounts were shot and so I replaced all of them ( I didn't drive the car until the mounts were changed so I cant be sure if it had this problem before I got it). When poking around for other possible locations for a leak I noticed that the top drivers side engine mount connects to a cover that attaches to the top of the engine and to the aluminum portion of the inlet manifold. Perhaps the vibrations from the old bad engine mounts have damaged the gasket, but only a little, just enough so that on acceleration, as the engine tilts back towards the firewall the inlet manifold 'hangs' and temporarily opens a tiny gap?


This is just my latest hypothesis and I'm not sure how to test/diagnose it other than replacing the gasket. I thought about removing or loosening the bolts that connect the mount cover to the manifold and taking it for a spin - the theory being that it would free the manifold to move more easily with the rest of the engine and may stop or reduce the gap? But I thought this might be a little foolhardy and I could end up damaging something else.


There doesn't seem to be any similar topics on any of the Renault forums that I can find, apart from an unanswered question on the Megane II Owners Club, which makes me think its either glaringly obvious or as obscure as an 'intermittent inlet crack only on significant engine tilt'.


Any help or suggestions that can be offered would be much appreciated - hopefully I can work out a testing procedure that will allow me to stop throwing parts at it and actually repair it...


Cheers.
 

Super mod..
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29,429 Posts
Hello everyone! This is my first post on this wonderfully useful site, been perusing its pages for a while now. I'm hoping someone might be able to offer some help with a seemingly unusual problem.

My 2005 2.0L 16v Megane II (F4R engine) is making an odd hissing/blowing noise similar to a very small turbo when accelerating hard or under load eg. up a hill. If I drive the car gently it doesn't make the noise at all and the car runs and idles very well. If I keep pushing the car once it begins to make the noise it will eventually misfire or skip and dramatically lose power until I release the accelerator.

I'm fairly sure it is a vacuum or inlet problem because of the misfire - sucking in excess air and making it run lean - plus it just doesn't sound like an exhaust leak to me, no ticking/tapping or inappropriate farty noises...

I checked all hoses and connections going to/from inlet manifold and couldn't find any cracks or holes so I ordered new inlet manifold gaskets - the ones between nylon upper and aluminum lower manifold sections, and the throttle body to inlet manifold gasket. When I removed the old ones they were all were pretty hard and rough looking. The area behind the join on cylinder number one had a small oil leak around it and that gasket was a little worse than the others. There was also a fair amount of oil in the inlet manifold, maybe 100mls or so.

After changing the gaskets there was a slight improvement in the noise ie. it seems to need to be pushed a little harder to make it misfire and skip. But the hissing/blowing is still there.

Next thing I replaced was the oil vapor valve, its hose and 'resonance' box that connects to the crankcase. I didn't expect them to be the problem but they were the originals and seemed a little gummed up with oil, changing them made no difference.


Given that I have checked and replaced the most obvious culprits, I am a little stuck and am now wondering about the gasket/shim between the lower inlet manifold and the block. When I first got the car the engine mounts were shot and so I replaced all of them ( I didn't drive the car until the mounts were changed so I cant be sure if it had this problem before I got it). When poking around for other possible locations for a leak I noticed that the top drivers side engine mount connects to a cover that attaches to the top of the engine and to the aluminum portion of the inlet manifold. Perhaps the vibrations from the old bad engine mounts have damaged the gasket, but only a little, just enough so that on acceleration, as the engine tilts back towards the firewall the inlet manifold 'hangs' and temporarily opens a tiny gap?


This is just my latest hypothesis and I'm not sure how to test/diagnose it other than replacing the gasket. I thought about removing or loosening the bolts that connect the mount cover to the manifold and taking it for a spin - the theory being that it would free the manifold to move more easily with the rest of the engine and may stop or reduce the gap? But I thought this might be a little foolhardy and I could end up damaging something else.


There doesn't seem to be any similar topics on any of the Renault forums that I can find, apart from an unanswered question on the Megane II Owners Club, which makes me think its either glaringly obvious or as obscure as an 'intermittent inlet crack only on significant engine tilt'.


Any help or suggestions that can be offered would be much appreciated - hopefully I can work out a testing procedure that will allow me to stop throwing parts at it and actually repair it...


Cheers.
Welcome to R/F..post approved so off you go..:smile2:
 

Super fantastic Mod Technical Supremo Nice Guy
Joined
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Can you try this .. will need a helper

Get a large cloth/rag,, hold it over the exhaust tail pipe, .but tell helper to stand at the side of the exhaust
Now start to rev , note what happens.. Slowly pressing the accelerator here.

Once at 3,000 revs, remove cloth,, just make sure whoever is at the back is standing at the side , as if any part of the exhaust baffle is faulty, it could well shoot out..


If the baffles, or lining in the exhaust are failing/dropping, then your symptoms match this

Exhaust gases cannot get out, but the gases need to go somewhere, .. your hissing
Now you releasing the pedal, exhaust gases can now slowly escape.
 

Registered
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You can try getting a pump and a latex glove/balloon/whatever works. Make a hole in the latex glove and put the hose from the pump in there. Now put the large opening from the glove on the intake.
You could make an extra step securing those openings, maybe with a zip tie or whatever your find handy.
Now you pump air and listen for any leaks. Change the location of the testing as you see fit.
Another variant is getting a jar, a hose, a latex glove, an air pump, baby oil, a rag and a soldering gun. You put some baby oil on the rag, then put it in the jar. Make 3 holes in the jar's cap: for the soldering gun to enter and make contact with the rag; for the pump hose to enter; for the other house to enter. Secure those in place with whatever you want. Now connect the free hose to the latex glove, secure it in place, then connect it to the intake. Turn the soldering iron on, wait for it to smoke the jar, then start pumping air at the rate to see fit and watch for smoke coming out of cracks.
Now you have a car that Vapes.
You can replace the ingredients as you see fit, just don't get the car too high, as it's not safe to drive like that.
 

Registered
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Discussion Starter #5
Thank you for the quick responses, I should have mentioned I tested the exhaust in much the same way when I first noticed the sound and I couldn't really hear or feel anything odd other than annoying the neighbours...:grin2: Nevertheless I will give your version of the test a try when I next have a chance, it sounds as though it might produce a little more pressure in the system.


Will also try the inlet test you suggested Mike, I have been trying to work out a way to leak test that part of the system. I have a small air compressor that I can hook up, I'm assuming it will need a fair bit of air because of the inevitability of some blow-by, so this will be a useful method. My only problem will be getting hold of some Gitanes or Gauloises for the 'vaping machine' - I'm assuming that is what a Renault would prefer.:franco:


I recently got hold of a Renault CLIP diagnostic system to see if that would give me any further info - nothing doing there unfortunately, just three minor faults recorded, all to do with the doors (which seem to operate just fine).


Thanks again for the replies guys, I will update the thread as I try things out.


All the best.
 
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