Discussion
You seem certain its the AFM? Another component possible to make the noise described 'during deceleration' is the over-run valve. If you have one, you'll be aware that it can be adjusted to modify its behaviour.
If the spring is loaded, by pure chance, to allow the valve plate to resonate in sympathy with all its associated pipes, etc, I guess it would be like a sweet spot on a trombone. It can also have it's valve plate jammed by small debris causing it to harmonise. If you are minded to, take the Over-run valve apart and give it a good clean.
Note the setting of the adjusting nut and for an experiment set it to the recommended position of '5 turns out from fully home'. Your engine exhaust will be less likely to pop and bang at my suggested setting, but I must admit I don't know what would be the optimum setting for a 3.9. Trial and error, perhaps??
If you want to know more about how this little jigger behaves I have written two excellent (*) articles describing function and scientific analysis. But then I would say that, wouldn't I?
Because you describe the harmonising as increasing 'more and more' also have a look for the beginnings of a rogue air leak in one of the tubes, pipes gaskets that must have 100% integrity. Sure, the engine is currently running without any noticeable issues but perhaps, soon, as the condition deteriorates some more symptoms may arise.
If the spring is loaded, by pure chance, to allow the valve plate to resonate in sympathy with all its associated pipes, etc, I guess it would be like a sweet spot on a trombone. It can also have it's valve plate jammed by small debris causing it to harmonise. If you are minded to, take the Over-run valve apart and give it a good clean.
Note the setting of the adjusting nut and for an experiment set it to the recommended position of '5 turns out from fully home'. Your engine exhaust will be less likely to pop and bang at my suggested setting, but I must admit I don't know what would be the optimum setting for a 3.9. Trial and error, perhaps??
If you want to know more about how this little jigger behaves I have written two excellent (*) articles describing function and scientific analysis. But then I would say that, wouldn't I?
Because you describe the harmonising as increasing 'more and more' also have a look for the beginnings of a rogue air leak in one of the tubes, pipes gaskets that must have 100% integrity. Sure, the engine is currently running without any noticeable issues but perhaps, soon, as the condition deteriorates some more symptoms may arise.
Edited by honestjohntoo on Thursday 3rd July 12:10
Thanks Honestjohn....Cool if its starting to behave like a Trombone, I play the saxophone so it would be nice to do a duet with my Wedge...
The idle control valve was cleaned and new gaskets were fitted a short while ago...The noise was there before this and is there now?...All of the air/Plenum hoses are regularly checked and i actually checked them again this morning.
Its definitely coming from the AFM area...I have gently cleaned the opening of the AFM and as much of the internal flow chamber as i could..I have cleaned the air filter and re-fitted using oil to seal the edges...I have a spare AFM so when i get it back i will see if the one does it...If its nothing to worry about then I'm not going to start messing with it as (Touch wood) she seems to be running okay....Cheers....Ziga
The idle control valve was cleaned and new gaskets were fitted a short while ago...The noise was there before this and is there now?...All of the air/Plenum hoses are regularly checked and i actually checked them again this morning.
Its definitely coming from the AFM area...I have gently cleaned the opening of the AFM and as much of the internal flow chamber as i could..I have cleaned the air filter and re-fitted using oil to seal the edges...I have a spare AFM so when i get it back i will see if the one does it...If its nothing to worry about then I'm not going to start messing with it as (Touch wood) she seems to be running okay....Cheers....Ziga
honestjohntoo said:
OK, but what is the 'Idle control valve' that is spoken of? Is that peculiar to a 3.9?
Sorry for the confusion...I stand corrected..I have an "Overrun valve"...Not sure where i got.."Idle control valve" from?...By the way its a 3.5 and not a 3.9...Wishful thinking me thinks....Cheers...ZigaPS: Forgot to say...I re-fitted the air filter again and the noise has gone?.....
Edited by mrzigazaga on Friday 4th July 11:53
http://en.wikipedia.org/wiki/Lucas_14CUX
It seems not - Rangey only (and the usual gaggle of sports cars).
It seems not - Rangey only (and the usual gaggle of sports cars).
mrzigazaga said:
Sorry for the confusion...I stand corrected..I have an "Overrun valve"...Not sure where i got.."Idle control valve" from?...By the way its a 3.5 and not a 3.9...Wishful thinking me thinks....Cheers...Ziga
PS: Forgot to say...I re-fitted the air filter again and the noise has gone?.....
I think you've fixed it Zig, on to the next challenge.PS: Forgot to say...I re-fitted the air filter again and the noise has gone?.....
Edited by mrzigazaga on Friday 4th July 11:53
V8 Fettler said:
I think you've fixed it Zig, on to the next challenge.
Seems that way mate...Thing is i think its down to the air filter being a slightly different size due to it being a modern equivalent , The two plates that its sandwiched in-between need to be re-made a tad wider in circumference to fit the edges of the K&N and this would help to seal it up better...I have tried some large "O" rings but they failed miserably, I could try a sponge type seal as suggested but i think the plates are the problem...I supposed i could just change to a conical K&N but think the volume of intake will be less....Cheers...Zigamrzigazaga said:
Seems that way mate...Thing is i think its down to the air filter being a slightly different size due to it being a modern equivalent , The two plates that its sandwiched in-between need to be re-made a tad wider in circumference to fit the edges of the K&N and this would help to seal it up better...I have tried some large "O" rings but they failed miserably, I could try a sponge type seal as suggested but i think the plates are the problem...I supposed i could just change to a conical K&N but think the volume of intake will be less....Cheers...Ziga
As I recall, I made a sealing ring out of a coolant hose for a similar issue.
As mentioned fella its really easy to see if the seal is causing the farting noise.... Just take the air filter off and run the car and test .... simples....
As mentioned and as I have heard it, I think its the AFM flap bouncing about due to a weak spring . Get your other one on there and test...
Chris
As mentioned and as I have heard it, I think its the AFM flap bouncing about due to a weak spring . Get your other one on there and test...
Chris
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