Technical Compresion test

[johnnyk]

Hi,
just done a compression test on my 1.2 8v Punto.
The results are 3 cylinders on 12 bar and one on 12.5 does this seem ok?

Thanks

John

 

[fingers99]

OK ish. If it eere a race engine you'd pull it apart, but ......... Did you do them with the engine up to temp and throttle fully open? A wet test (teaspoon of oil down the plug holes) might indicate why 3 are lower.

 

[johnnyk]

Thanks for the reply,
I`ve just tested it again, warmed up and throttle open.

I got 14 , 12 13 and 14 bar.
The engine has a miss fire, not loosing oil or water.

Just replaced the H T leads, no better.

Are we thinking head gasket?

Thanks again

John

 

[fingers99]

Could well be. How is it on start up?

 

[johnnyk]

starts easy

 

[bredsticz]

If there's no other signs of head gasket, it could be your piston rings are worn or cracked cylinder head, there's not a major difference though i wouldn't worry too much so long as she's driving ok. I just did compression test today and got 12,8,12,12. Not good

 

[johnnyk]

Car has an intermitent miss fire, so ignoring it isn`t an option.

Pushing it off a cliff sounds good though

 

[fingers99]

If there's no other signs of head gasket, it could be your piston rings are worn or cracked cylinder head, there's not a major difference though i wouldn't worry too much so long as she's driving ok. I just did compression test today and got 12,8,12,12. Not good

Both of you should do a wet test, too (helps tell if the bores or the valves are the culprit). Two adjacent cylinders down is a fair indication of HG failure.

I've yet to come across a cracked head on a FIRE engine.

 

[rallycinq]

Lumpy idle is indicative of headgasket failure between two cylinders.

If this is suspected, watching the compression tester as you turn the engine over will show double pumps.

Cheers

SPD

 

[Noddy]

My experience is that it tends to be the valves that are the problem (to the point I have a speare cylinder head all ready to go). Have never had any other problems with rings or cracking etc.

 

[johnnyk]

Had the car on a diagnostic machine to day and it refused to missfire, replaced both coil packs, seemed to do the job.