Talk Morgan Forums Morgan Sports Cars Classic Morgans (pre-CX) +8 Engine Noise

I have a 1990 Plus 8 3.5 EFI which I've had from new and has 32K miles on the clock. It has developed an engine noise at exactly 2600 rpm, take the speed up to 2700 and the noise disappears. It is a very high pitched whistle and my initial diagnosis was that it sounded like air being drawn into the plenum chamber or maybe a hose connected to the plenum chamber. The noise is exactly the same irrespective of engine load. Due to general engine noise it is difficult to determine which area it is coming from. I am going to remove the fan belt to eliminate the alternator and water pump but I believe this is a long shot as it is not your typical bearing noise. I'd appreciate any suggestions, particularly if you have experienced this type of noise on you +8 EFI

Check the inlet manifold bolts to the head for tightness, you can also get air leaks at the butterfly spindle.
Does it tick over fast?

A way to check for air leaks around the inlet is with a can of easy start (but be careful of fire from a wayward spark) if tickover increases thats where the leak is.

David Byrne

Check the fan belt. It is a known location for “belt squeal” or slight belt slip. My car had that and I cured it by taking the belt off and cleaning the pulleys and wiping the belt clean. I think ( it was several years ago) I used brake cleaner on a cloth for the pulleys to avoid overspray onto bearings etc and meths on a cloth for the belt. Refitted the belt and tensioned it. No noises after that. The noises pre cleaning came and went as revs changed and MIGHT be the case with your car. A simple job that can find or eliminate the cause.
Gomog has a section on it and another option was to replace the belt with a slightly narrower one.

Without more information this one is gong to be challenging.

There will always be a high pitched whine/whistle from the induction intake . Do you have the original "black cylinder" with a circular air filter inside? Or have you upgraded to less restrictive type (cone etc)

It does sound like something on the air intake side , so I would be checking the air filter , the "black box" and the air mass/air flow sensor (do you have 13 CUX "Flapper", or 14CUX "Hotwire"?) for leaks and correct functioning . It is unlikely to be within the inlet manifold , but I guess we can't rule it out yet. Also check all of the rubber connectors and electrical connections into the plenum. You may have an air leak there.

Can you attach an audio file with a recording of the sound?

Thanks to all above for your replies. I will check the fan belt when I remove it as I want to rule out the alternator and water pump although I'm still convinced it is more of an air leak on the induction system. The air intake hoses, air filter element and filter box are all standard factory fitment (ie round plastic filter housing). Idle speed has not changed. The EFI is flapper type. My next job is to physically check all of the induction connections and plenum chamber for possible leaks. I will attempt an audio recording