Technical Misfiring 1.2 16v Sporting

[AlanHealy88]

Alrite people,my Punto is Misfiring,we changed the plugs and still the same..Done a compression test and Cylinder 2 is reading 75 where as the others are 125 and above...

Any idea what could be the problem?
The car has 100,000miles on it if that makes any difference.

 

[Martin NI]

Could well be a blown head gasket

Martin

 

[AlanHealy88]

Its not the head gasket nyway...She aint taking water or nutin or over heating

 

[beau]

head gasket gone between oil ways not water or cracked head, or piston ring.

 

[AlanHealy88]

i was thinking maybe inlet valves or sumtin???

 

[reddy4bed]

Squirt some oil into plughole and see if compression improves, if it does its rings, if it does not its valves. Doubt if head gasket is the problem because that escape of gas would cause obvious problems elsewhere.

 

[AlanHealy88]

nice 1 bud,ill shall try that

 

[The Sultan]

have you just changed oil it could be a hydraulic tappet jacking a valve open if you have used the incorect oil grade

otherwise just go buy the threat above

you need 110 psi for proper combustion as a guide so your right in the diagnosis of poor compression if you have measured it properly as said try with oil

if you have a means to blow into the spark plug hole you can set the engine on top dead on the dodgy piston with both valves supposedly shut and see if you can hear it leaking out the inlet manifold or exhaust obviously unless you split the front pipe you will find it difficult to hear it in the exhaust but inlet will be vary audible worth a try a very good way to rule out burned valves but wont show up a valve jacking problem as it willl have settled shut again

also make sure there is no arching from the plug leads and no burn marks around the base it's very very common on 16v engines when plug gaps get to big they burn the leads

th3e best way to diagnose this is wile it's running pull the lead just off the top of the plug but do not expose the plug top from the bottom of the insulation

normally in this situation the spark will jump for the plug every time but if the lead is shot it will jump out the side into the head every time you will see and hear this like someone clicking there tongue kind of sound