Bad Compression on one cylinder?

[NorGodzilla]

Recently my R32-GTR started running really rough at all rpms, so i did a compression test. 

the results: 

Cylinder 1: 165 

Cylinder 2: 165

Cylinder 3: 130 => 165 when doing a wet test.

Cylinder 4: 155

Cylinder 5: 165

Cylinder 6: 175

Cylinder 3 with 130 concerns me, do i need a rebuild? should i check for other reasons my engine is running bad? and what could cause this (suspect its the infamous ringland) i also have pressure in the sump, but no smoke from the exhaust. 

extra: i have changed, injectors, plugs, coil, ignition module and wiring loom so far. 

Thanks for all replies! :) 

-NorGodzilla

[GTSBoy]

Given the evidence of a significantly different cylinder health, of course it could be to blame.

However, just about everything else on the car could be responsible. AFM, CAS, wiring and connectors for each, coil loom, dirty/dud injector and/or the injector loom. Low fuel pressure from failing pump, boost rag, blocked cat, burnt valve, chipped cam lobe, timing out, valve timing jumped a tooth.....do you want me to go on?

[NorGodzilla]

I get that there is alot that can cause this. i have checked the cas, maf's, injector filters, fuel pressure, i dont have a cat, i have a new coil loom, timing, and that the timing belt has not jumped a tooth. still i understand that there is a hundred more things that can cause this. anyhow thanks for the input.

[tridentt150v]

The difference between a dry and wet test says bore issues, rings, lands, gudgeon out etc to me.  Can you get a bore scope and have a look, you might see marks on the wall?

[GTSBoy]

46 minutes ago, tridentt150v said:

The difference between a dry and wet test says bore issues, rings, lands, gudgeon out etc to me.

Oh yeah, but while the compression was a bit low, it probably isn't low enough to cause rough running on its own. I mean, it might, but it's just as likely to not. Hence why I gave the laundry list. Many other things more likely to cause rough running than a cylinder down 15% or so.

[tridentt150v]

On 13/07/2020 at 1:24 PM, GTSBoy said:

Oh yeah, but while the compression was a bit low, it probably isn't low enough to cause rough running on its own. I mean, it might, but it's just as likely to not. Hence why I gave the laundry list. Many other things more likely to cause rough running than a cylinder down 15% or so.

Very true, I wasn't really thinking of the rough running issue when I replied.   I guess he went hunting rabbits and looks like he might have shot a squirrel

[NorGodzilla]

On 13/07/2020 at 4:36 AM, tridentt150v said:

The difference between a dry and wet test says bore issues, rings, lands, gudgeon out etc to me.  Can you get a bore scope and have a look, you might see marks on the wall?

i have now taken a look with a camera on the cylinder walls, it seems like there is a decent amount of scratches in all cylinders, i suspect this is just normal wear, due to the engine being almost 30 years old. in cylinder 3 there seems to be one scratch that is alot deeper than the others, this one seems to be quiet deep into the cylinder wall. i understand that this can explain the pressure in the sump and blowing out the dip stick. do you guys think i should continue searching for other issues that may cause the engine running rough, or should i pull the engine now, any suggestions on what to do?

[GTSBoy]

Well, look, the engine is f**ked right now. You should rebuild it just in case that scratch is the warning that something is about to break away/seize the piston/wreck a valve/turbo/etc.

If you do that, then whatever the very likely other cause of the rough running will still be there when you try to start up the freshy and run it in, which won't be good.

So fix both.