Engine resonance

Q A year ago, I bought a 2007

Morgan Plus 4 with a 2.0 Duratec engine that has covered 35,000 miles. There is a resonance when accelerating that occurs in the region of 2500rpm, both on- and off-load. It’s OK at lower and higher engine speeds.

At first, I thought it might be a loose component in the exhaust system. However, checking the engine when stationary, it seems to vibrate at those revs. I am currently not sure if this is a mechanical or fuelling issue. If mechanical, I guess the flywheel could be a suspect. I think these engines are supplied by Ford Industrial and don’t know which flywheel they fit. Performance-wise the car seems OK, with a bit of pinking noticeable on occasion, but I assume the ECU adjusts the timing to eliminate this when it occurs.

Apart from the flywheel, are there any other components that could be out of balance or causing this slight vibration? Is there a decent workshop manual available for the Duratec engine, including the fuelling and emission control components? I have a Haynes manual for the Mondeo, but they don’t go into much detail, so it is not possible to identify some components. I was trying to see if the engine had swirl flaps – there seems to be a vacuum-operated servo under the throttle body, but I can’t see a connection to a driveshaft. Mike Smith

A From the data I have, the Morgan Plus 4 has a standard sprung centre-plate with a solid flywheel and uses the Mazda GETRAG five-speed transmission. The engine is the Ford Duratec 20 unit, which is part of the Mazda MZR range of engines. Your manifold should not have swirl flaps and I am unsure what the vacuum component is that you can see. It may simply be a supplementary vacuum reservoir fitted by Morgan as part of their engine tuning measures.

Any vibration in the engine would be more likely to be due to a mechanical problem than misfuelling, unless the vibration was the result of a misfire although, from your description, I don’t believe this to be the case. The most common area of such problems is the exhaust system or manifold, but as you’ve already checked this it can hopefully be discounted.

If the type of vibration is in doubt, I would recommend connecting a diagnostic scanner to ensure that the parameters are all even when the engine is running at 2500rpm. Any anomalies between cylinders should clearly show up on a live data graph.

The camshaft drivechain may cause a slight resonance if the tensioner is not operating correctly or if the chain has stretched, but this is not something I would expect to see on an engine with only 35,000 miles. In the same area of the engine, it is possible that the automatic belt tensioner for the auxiliary drivebelt is the source of the vibration, and I would check this with the engine running at 2500rpm to ensure it is not unduly bouncing around.

As the noise is most apparent when accelerating, this may suggest inlet manifold problems and I would also check the induction system for any areas that the sound may be coming from. Another area worth inspecting is the engine mounts – these too can be the source of such a vibration.

Finally, I am unsure which sump will be fitted to your Morgan, but if it is a low-line unit (slimmer than the standard sump) these do have internal baffle plates to maintain a constant oil feed on harsh cornering. It may be that one of these baffle plates is resonating at a particular engine speed.