I have an mx5 that sometimes starts on 3 cylinders - any ideas?
It also has a rough idle when coasting - any help would be much appreciated.
Answers:
Pull out all four spark plugs and have a look at the electrodes - they should be a light grey, not black, greasy or covered in soot/ash. The mx5 engine (both the 1.6litre and the 1.8) have the plugs sunk deep into the rocker cover - you'll need the extension tube in the supplied mazda toolkit to get them out.
If you hold the outer bit of the electrode against the engine you can have a friend crank the engine with one plug out and see if it sparks. Try this for each plug. Of course there are multitude other things it could be but this is a simple(free!) test to do at home.
if you can reproduce the misfire try getting a mobile engine tune guy around with a diagnostic machine they can see whats going on a oscilloscope
Maybe change the HT leads, they can deteriorate over time and lose the charge they are holdinh, especially when wet.
Try :
mx-5.com
mx5oc.co.uk
clubmazda.co.uk
mx5nutz.com
mazdaforum.co.uk
I hope this helps.
Plugs and leads. Make sure you have the best quality, correct type of NGK plugs fitted, and a set of OE Mazda HT leads. If you can change the distributor cap at reasonable expense, then do so. Many cracks in caps are invisible to the naked eye.
I doubt it's anything to do with the plugs or leads. They tend to either work or don't work. It sounds to me like you've lost compression on one cylinder.
Have a look under the oil filler cap to see if any water has mixed with the oil (there will be a white sludge if it has) or look in the radiator header tank to see if there is any oil in there. If there are signs that they've mixed, then your head gasket has gone and that is what is causing the low compression & dodgy starting.
If there is no sign of oil & water mixing you need to get a compression test done. This will show if the head gasket has gone between two cylinders which would cause the symptoms you describe without affecting the oil and the water, or it'll show if you have a more serious problem like a burnt out valve.
hope this helps.
dodgy plug leads invisible water leak into cylinder are you losing any water?
I would replace the plugs and wires first as Miata's have a common problem with plug wires.
Bad plug wires and plugs usually misfire under load. It takes more voltage to fire a plug when accelerating for example. If the plugs are fouled or a bad wire, the spark will jump to ground rather than fire plug.
A bad fuel injector will flood one cylinder until car gets running and cleans it out. Try pulling plugs after cold start when engine is missing. If plug is wet, that is your problem and that cylinders injector.
Miata does not have a distributor cap. It has a crank angel sensor that signals 4 coil pack. Hard to clean or replace something that does not exist.
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