m16 220GTi - Missfire on Overrun [Archive]


MG-Rover.org Forums > Model Specific Forums > 'R8' Rovers (aka Wedges!!) > m16 220GTi - Missfire on Overrun PDA : m16 220GTi - Missfire on Overrun undaflip 23-12-2002, 12:14 My car has a misfire on overrun - not apparent when when accelerating - its not a continuous stutter, but only a single "jump" about every 0.4k decrease. It has had this through various changes of leads/dizzy etc - what else can cause a missfire and would cause it on overrun only? It has been a long term problem with the car, and various "fixes" have been tried (Leads/dizzy/sparks, injectors cleaned, HG, lots more), but the missfire inevitably comes back fairly soon after. Can anyone write a definitive list of things to check, and an order of checks to be employed - both electrical and mechanical - even remote causes, and one-in-a-million chances. When the car has run smoothly its a joy, but its only ever run smoothly for about 5000 of the 30000 miles I had it for......... Many thanks, Dom undaflip 24-12-2002, 10:53 Are there many mechanical causes for a misfire? I appreciate that water in the cylinders might cause this, but had the head off at 103K for new gasket set, head mods - Head gasket obviously changed, but overrun missfire still apparent. I am assuming that most causes are likely to be electrical - what are the less obvious causes?? Dr Dave 24-12-2002, 17:30 You cannot have an over-run misfire - the engine is running down - usually no fuel is injected [over-run fuel cut off] I'm puzzled - maybe it is the fuel cutoff that is causing the problem? undaflip 03-01-2003, 13:10 A long trip to London showed me that the missfire is actually happening most of the time, but under acceleration/cruising it is not-very-noticable, although you can feel it if you "look" for it. It becomes much more noticable on overrun, or whenever the foot is taken off the accelerator - an initial misfire (or jolt - engine rocking on mountings? quite noticable tho'), then at intervals (however not rapid) of about 0.4k revs What parts would this revision of facts point towards, as being the culprits? Many thanks, Dom cosb6 03-01-2003, 13:34 Sounds like a fueling issue to me?... Maybe Fuel sensor? / Air sensor? Seems odd though.... undaflip 03-01-2003, 13:57 Is there any way of testing the integrity of these sensors, or is it just a case of "replace & see" ?