Moans on overrun

[deetes]

Since converting my TVR 390(flapper EFI) to MS, fuel only, it makes a strange moaning noise on overrun. This will go as soon as the throttle is pressed again, even very lightly. I'm assuming it's air being sucked in through the closed throttle plate in the plenum, but I assumed that the by-pass idle system would be able to cope with that.
Perhaps another factor is that I repositioned the air filter near the bulkhead and possibly it always did this, but I didn't hear it.
Any suggestions? Preferrably helpful ones.

[ramon alban]

Since converting my TVR 390(flapper EFI) to MS, fuel only, it makes a strange moaning noise on overrun. This will go as soon as the throttle is pressed again, even very lightly. I'm assuming it's air being sucked in through the closed throttle plate in the plenum, but I assumed that the by-pass idle system would be able to cope with that.
Perhaps another factor is that I repositioned the air filter near the bulkhead and possibly it always did this, but I didn't hear it.
Any suggestions? Preferrably helpful ones.

I'm speculating here but, if there was one originally, did you leave the overrun valve on the rear of the plenum chamber?

If so the vacuum generated in the inlet manifold on overrun may be sucking in via that path.

They do moan a lot when the vacuum is high.

[deetes]

Ramon,

Never heard it moaning before, but as I mentioned I moved the inlet up to the back of the engine compartment and it's just more audible in this position.

Do the overrun valves fail? Could this cause the moan?

Thanks anyway

deetes

[ramon alban]

Ramon,

Never heard it moaning before, but as I mentioned I moved the inlet up to the back of the engine compartment and it's just more audible in this position.

Do the overrun valves fail? Could this cause the moan?

Thanks anyway

deetes

No, their job is to open when there is a high vacuum, and if you look at the construction, as the spring opens so does the valve and this relieves the vacuum so the valve may shut again and the vacuum then opens it again, setting up an oscillation and making a noise.

I asked if you have still got it on the rear of the plenum? also is it used on your current setup?

If you do not use it and it is opening to atmosphere then the noise will be more noticable. If it is still there block it off or remove it.

[deetes]

Ramon,

It's been on the car since I bought it. I assume it was part of the original flapper EFI system. Don't know if it works or not. Is it ok just to disconnect the hoses and block them off?

The AFM's gone and everything else is pretty much as Rover / TVR built it. Whether it needs the overun valve or not is beyond me.

Allan

[ramon alban]

Ramon,

It's been on the car since I bought it. I assume it was part of the original flapper EFI system. Don't know if it works or not. Is it ok just to disconnect the hoses and block them off?

The AFM's gone and everything else is pretty much as Rover / TVR built it. Whether it needs the overun valve or not is beyond me.

Allan

Allan, Me neither, not being familiar with MS and your modified setup I dont know what if any of the original components it requires.

It should be easy to test for valve moaning though.

Clamp off the input pipes to the overrun valve, or otherwise disable it, to prevent the valve opening under vacuum and see if the moaning goes away.