Compression testing

[Fazman101]

Hi. last month i blew my engine up so i got a scrapy engine. Anyway engine runs but it misfires. so i did a compression test got readings on all for between 13.5 - 14 bar. isnt that a bit high?

 

[frank]

the 5 speed 1.0,s were high comp eh (10.3:1 iirc) so fine if its one of those

 

[Fazman101]

its the 1.2 only done about 50,000 miles.

 

[rustyroger]

The important bit is not much variation between the cylinders, and good compression too.

New plugs and a thorough tune up should fix your misfiring.

Roger.

 

[Fazman101]

its got new plugs, oil filter and new oil twice. it starts fine after about 30 secs it starts to misfire and the exhaust starts steaming. Headgasket?

 

[davew]

Roger's quite right. Compression testing is a dubious art at best - depending upon accuracy of gauge (usually poor), seal to head, cranking speed, throttle butterfly position, amount of oil floating around in ring area, engine temp, etc etc.

Your readings are all about same so that's good. 15 bar is high!!!

If head gasket had gone a cylinder would have water in it when you started up and you'd have an instant misfire. Steam from the exhaust is normal - condensation burning off.

Does it tick over good when cold and when hot? Is the misfire only when revved or does it clear when revved?

If it misses on tick over and clears when revved I'd be thinking an exhaust valve. If it gets worse when revved, petrol, electrical??

 

[Fazman101]

Thank for that. it all sorted now. just got to make the brakes Work.