compression

[16v Nova Kev]

what should the compression be on my xe 124 are 125psi and 3 is down to75 just tested it today dont know where to start valves/headgasket/rings:(

[Adam]

They are all low.

Was it done with the throttle wide open?

[16v Nova Kev]

no thought it might fire with 3 plus engine cold so i warmed it up 1.2and4 went up to 200 and 3 was 150 tried oil down 3 and it went a bit up so think i need rings bummer

[Adam]

Do it with all plugs out, warm engine, with throttle wide open

[16v Nova Kev]

124 doing 140 3 is doing under100 its humped getting a block tommorrow with new rings and honed bores for free my m8 built it a while back total pisser man thought i was nearly there too:(

[meritlover]

did you do a wet test? its the only way to determine whether its valve or bore damage without removing the head or using a boroscope.

[16v Nova Kev]

if you mean pour some oil down the bore yes i did it made 3 a bit better. got a block today it has new rings/pistons/oil pump problem with it was it had a dodgey crank regrind so i will use my crank/shells/bigends with the new block and pistons

[16v Nova Kev]

got the engine stripped number 3 piston looks a bit melted at top edge so im going to fit new pistons and rings and get it honed

[meritlover]

you must find out why its melted, especially if the other 3 are fine.
check the no3 injector is not blocked causing a lean burn or Detenation

[16v Nova Kev]

funny that we changed no3 injector least year but never checked the compresion till last week must have been that

[meritlover]

was the injector you changed exactly the same? ie flow-rates identical?
it would be money well spent to remove all 4, get them flowed, cleaned and check they are a matched set.
sounds like thats been the problem