I doubt that viewers would be aware of the details of compressor filtration and, moreover, for those in the audience who are divers it would be plausible to them that an old compressor might not have a sophisticated filtration system anyway. Removing a filter cartridge would cause an immediate objectionable taste to the air although the audience might not appreciate this nuance and it therefore could be believable. However, tampering with an exhaust manifold would cause the engine tone to change and would be obvious and therefore not credible and make for a weak plot. Moreover, portable compressors are never positioned with exhaust up wind. Rerouting an intake hose would be visible and obvious and hark back to the hokey plots of old. However, it has dramatic license going for it. Everybody can see it and understand it. Isaac is right, adding a spoonful of kerosene to the compressor sump would likely cause dieseling and carbon monoxide. However, this kind of manipulation might be difficult to convey to the viewers of the film as it requires some knowledge of the issues on the part of the viewers. For example, a charcoal filter would remove the bad taste but not the poison. But, later, when the truth came out, the dramatic impact would be increased as Sherlock Holmes or somebody of similar stature revealed the scheme to an enthralled gathering. DA has a point but only if it were part of a scene where the compressor could be manipulated in a way which was not obvious to the scene's characters.
