80 PSI Cly 4 Compression and Leakdown

[BoscoGuo]

Hello everyone. I just did Compression and Leakdown test yesterday for my 2018 STI which is 38000KM. After I was waiting almost 4 hours outside, the machanic gave me the result of the compression and leakdown test.

Compression: Cylinder 1: 140 PSI
Cylinder 2: 140 PSI
Cylinder 3: 150 PSI
Cylinder 4: 80 PSI

Leakdown Test result: Cyl 1,2,3 are all pass, but Cyl 4 read 80% Leak. I also dont know why the leakdown result only shows "pass" without specific number.

My location is in Toronto CA, I am runing Cobb Stage 3 setup and Cobb OTS 91 MAP. Before I was runing 93 MAP but there is always too many Feedback knocks and Fine knock learn in this winter, yep!!!! it is only happened in this winter(usually greater than 4.2, always keep around 6, even a few times greater than 8, only one time FDK is 10!!!! and DAM has dropped down several times, but everytime I reflash ECU MAP, DAM went back to 1.000, that is why I change back to OTS 91 MAP) .the cobb stage 3 kit was done in Jan, 2020, I was runing 93 MAP before with Petro 94, Knock was not as bad as in this winter,ususally keep around 4.2

2 more weeks ago, I also tried to adjust timing to -5 via AP, I definitely read the both knock are less. but only omen I can image is a lot knocks and few times DAM dropping , but no any misfires, hesitating idle or something else. Chaning oil every 3000~4000km, warm up every single day when it is cold start before I send it, but also push it hard to many times. is it must ringland failure?

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[Blackfin]

With an 80% leak rate I'd expect you could easily hear air exiting the oil filler cap or dipstick tube when that cylinder was pressurized.

But yeah, low compression hand in hand with high leakdown usually means a ring land failure. This assumes there wasn't any evidence of bubbles or pressure in the cooling system or air escaping the intake or exhaust while that cylinder was pressurized.

[Jedi03]

dang...if you need i have an extra longblock palletized...

[Waddlz]

sounds like ringland failure

my 2012 had cylinder 4 fail with 60 psi compression, unknown leakdown. When I popped the piston out about 1/4 of the ringland was gone.

[r8888]

Originally Posted by BoscoGuo

Hello everyone. I just did Compression and Leakdown test yesterday for my 2018 STI which is 38000KM. After I was waiting almost 4 hours outside, the machanic gave me the result of the compression and leakdown test.

Compression: Cylinder 1: 140 PSI
Cylinder 2: 140 PSI
Cylinder 3: 150 PSI
Cylinder 4: 80 PSI

Leakdown Test result: Cyl 1,2,3 are all pass, but Cyl 4 read 80% Leak. I also dont know why the leakdown result only shows "pass" without specific number.

My location is in Toronto CA, I am runing Cobb Stage 3 setup and Cobb OTS 91 MAP. Before I was runing 93 MAP but there is always too many Feedback knocks and Fine knock learn in this winter, yep!!!! it is only happened in this winter(usually greater than 4.2, always keep around 6, even a few times greater than 8, only one time FDK is 10!!!! and DAM has dropped down several times, but everytime I reflash ECU MAP, DAM went back to 1.000, that is why I change back to OTS 91 MAP) .the cobb stage 3 kit was done in Jan, 2020, I was runing 93 MAP before with Petro 94, Knock was not as bad as in this winter,ususally keep around 4.2

2 more weeks ago, I also tried to adjust timing to -5 via AP, I definitely read the both knock are less. but only omen I can image is a lot knocks and few times DAM dropping , but no any misfires, hesitating idle or something else. Chaning oil every 3000~4000km, warm up every single day when it is cold start before I send it, but also push it hard to many times. is it must ringland failure?

your problem is you ran the wrong Map. Should have used ACN91, Toronto fuel is crap. The map ign is less aggressive. I believe it stated on COBB bulletin. Get a protune when you replace, your engine and don't send it when you see knock and DAM goes down.

[BoscoGuo]

Originally Posted by r8888

your problem is you ran the wrong Map. Should have used ACN91, Toronto fuel is crap. The map ign is less aggressive. I believe it stated on COBB bulletin. Get a protune when you replace, your engine and don't send it when you see knock and DAM goes down.

Definitely I know 91 and 93 MAP is not capable with best fuel 94 in Canada. I just cant stand it being to slow with ACN91. Actually I was planing to do a protune after Comoression and leakdown. But…… everything is too late***128514;

[BoscoGuo]

Originally Posted by Jedi03

dang...if you need i have an extra longblock palletized...

which one? Is that IAG?

[blurred]

Originally Posted by r8888

your problem is you ran the wrong Map. Should have used ACN91, Toronto fuel is crap. The map ign is less aggressive. I believe it stated on COBB bulletin. Get a protune when you replace, your engine and don't send it when you see knock and DAM goes down.

That bulletin was for western canada about a decade ago for fuels with 0% ethanol.
Fuel in toronto is good, just off the shelf tunes are not good for every car or he had mechanical issues that made it run badly. getting a proper tune is always the answer.

[Jedi03]

its a stock one, from a 2018 46k miles had great compression when pulled...am putting together a ridiculous build block that i am currently also debating about selling or running lol and motor in the car now is running great so dunno when i will actually need one, just figure keep it as an option for those in need!