UHF CH5 Engine Interferrence on GME4200

Hi Guys, and the Gals.

I am picking up engine interferrnce through my GME 4200 UHF CB on Ch5.

It's picking up the revs of the engine and when i accelerate, this is emulated through the GME speaker.
This causes hassle as i can't scan - the bloody thing keeps locking onto the engine!

I was told to go and buy a EMI block thingy.

As the car i have is a Mitsubishi magna '95 V6 3.0ltr, do i need to buy 6 'EMI thingys' one on each plug lead, or do i need one EMI thingy for somewhere else, or attach it to the GME somewhere?

I'm using a RF Ind 6db anntenna.

Is there any specification that i need when buying a EMI thingy - they look just like a ferrite core thing - for different cable thickness's upto 10mm.

Any help would be appreciated.

Thanks,
Alan.