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[Mr Gav]

My Omega is suffering a flat spot at 3500rpm on full throttle, it doesn't happen on part throttle and will pull through cleanly. It's fine below 3.5k and once it's past about 3.8k it revs cleanly to the rev limiter, I'm assuming it's something to do with the multi ram system but I would have thought if there was a fault with the multi ram it would affect either below 3.5k or above not just a small flat spot.
Anyone got any ideas or had similar problems?

[chrisgixer]

Breaking down spark plug? Or ignition issue.

[chrisgixer]

Multi ram would be above or below a certain rpm. About 4k is it?

[Mr Gav]

Plugs and leads got changed about 8k ago along with the can cover gaskets and cleaning out the breather box and the plug wells are still dry.
Not sure about the multi ram set up on the omega, there is a change over point, does it start at 4k and fully open at 4.5k or does it start at 3.5k and fully open at 4k?

[chrisgixer]

Ime it's flat above or below 4k depending on which multi ram is failed.


I suppose it could be slow vac leak affecting high rpm ...?

[Mr Gav]

The puzzling thing is it`s fine once it`s pulled through the flat spot, which only happens for about 3-400rpm, once it`s above 3.8/3.9k it flies.
Like you say if it was a multi ram fault it would affect either the high rpm or low rpm, it`s not a major problem but it`s just irritating   

[chrisgixer]

Had 2.2 round here that did the same. Spark plug was arcing down the side leaving a black track on the porcelain. Ran fine above 4k odd, and below 3k. Just refused to run at that rpm range.

Has it leaked in gradually getting worse, or arrived suddenly one day?

[Andy H]

Sounds a bit like the issue Webby had with a failed non return valve in the front vacuum tank

[chrisgixer]

Can we define the flat spot a bit? Just to be clear....?

Ie are we talking what feels like a lift on the throttle, when it's actually pinned to the floor? (Multi ram)

Or more of a cutting out or a stutter through that Rev range? (Ignition brake down)

..?

[Mr Gav]

Can we define the flat spot a bit? Just to be clear....?

Ie are we talking what feels like a lift on the throttle, when it's actually pinned to the floor? (Multi ram)

Or more of a cutting out or a stutter through that Rev range? (Ignition brake down)

..?

It feels like a bit of a stutter but the throttles pinned to the floor, It`s like it`s hesitating and then it clears it`s throat and flies just for those few hundred rpm. Can`t say how it arrived though, one of those things thats been niggling for a while but other things have taken precedence and I`ve just suffered it while I`ve been getting to grips with the crap hanling 

[chrisgixer]

I'd suspect a miss fire tbh.

Plugs still tight?

[Mr Gav]

It doesn`t feel like a misfire, I think for the cost of it I`ll just buy some new plugs to eliminate them and take it from there.
Because it happens at the same revs every time and for the same duration i was inclined to think it was a multi ram issue, the misfire I had before felt completely different.

[chrisgixer]

Miss fires reveal themselves in very different ways ime. From a completely dead cylinder to a slight miss at tickover to dropping one cylinder for a few rpm in the middle of the range under heavy load. There's no real rule to a miss fire IME.

[4x4]

Coil pack on its way out could be another possibility.

[Mr Gav]

I'll change the plugs first and take it from there.
I don't think a session on tech 2 would harm as I'd also like to get my climate on the latest firmware, anyone know who the nearest person to west Yorkshire is?