low compression in 3 and 6 / t/t 89 2+2

i need some help diagnosing this low compression issue..

when i bought this t/t no.6 wasn't firing ...when i got it home i changed the plugs and coil packs and started firing and idling good....at one stage it ran very low on petrol than its ever been and i have ever seen, then after re fueling no. 6 stopped firing at idle and at higher rpm's it would kick in...i initially put it down to possibly a partially blocked injector.

so today i did a compression test, cold engine ,cas unplugged, throttle open, all plugs removed...so, 1,2,4,5 had good readings between 150-160
3,6 were very low 90 and 50

1/

2/

3/

4/

5/

6/

i poured a little oil in 3 and 6 and the readings improved a little but not much

3/wet
6/wet

while i had the plugs and coil packs off i attempted to do a leakdown test
and it seems 3 and 6 under pressure can hear the air in the plenum

would that mean the rings are gone?
any input will be appreciated

 

bad rings will typically cause air to come out the dipstick tube during the leakdown test. air coming from intake plenum would indicate intake valves allowing air to pass.

how did you get each piston to TDC for the leakdown test?

 

im not adept at doing leak down test, this was my first attempt...with screwdriver, felt for piston through spark plug hole, while turning the crank manually...

so if i wasn't TDC would that show me something inaccurate ?

 

lysergic has raised a valid point about the cylinder under test being at TDC on the compression stroke, if it isn't, valves could be open.
However that won't affect the compression test results.
Hate to be the bearer of bad news, based on your results, it would appear maintenance is required on that engine.
You mentioned oil was added to the cylinders in question which didn't noticeably improve the figures.
This would normally indicate valve related issues or possibly severe piston/ring/bore damage.
Prior to dismantling perhaps a borescope inspection is warranted.

 

you probably have a couple of melted pistons ,due to the boost being wound up,the head has to come of ,so you might as well pull out the engine and put it on a stand first. if you can get hold of a bore scope ,that will tell you more.

 

thanks for your valued input
yes...i am aware that this motor is in need of maintenance ! ive been expecting the worst ....

im going to do the leakdown test again so im 100% sure each cylinder is at TDC...also , is it recommended doing it when motor is up to temperature ?

and, i will try and source a borescope...

thank you ...ive got a PM incoming

so please tell me how you arrived at that diagnosis ??
boost was NOT wound up!

and i have all intentions in pulling the motor as i want to do the turbo's and possibly some other work

thanks