1G Low compression readings on all cylinders

[dsm_jeb]

I have been recently diagnosing and fixing various performance issues on my mostly stock 6 bolt. I found that I had a boost leak into the crankcase. I did a compression test with the engine warm and the throttle open. Cylinder 1 and 2 were about 70 psi dry and 80 psi wet. 3 and 4 were about 80 dry and 90 wet. Each cylinder was test three different times. My question is what is the most likely cause? I would imagine even if the rings were toast that the compression readings would have substantially increased with oil in the cylinder. Although I have noticed the car runs very hot even with an mishimoto radiator I wouldn’t think that the brand new MLS headgasket would be blown. Any input or advice would be appreciated. Thanks!

 

[92AWDHX40]

Time to pull the head and check everything out.

 

[dsm_jeb]

Time to pull the head and check everything out.

So likely not rings?

 

[92AWDHX40]

Hard to say could be hg or rings

 

[DSMPT]

I have been recently diagnosing and fixing various performance issues on my mostly stock 6 bolt. I found that I had a boost leak into the crankcase. I did a compression test with the engine warm and the throttle open. Cylinder 1 and 2 were about 70 psi dry and 80 psi wet. 3 and 4 were about 80 dry and 90 wet. Each cylinder was test three different times. My question is what is the most likely cause? I would imagine even if the rings were toast that the compression readings would have substantially increased with oil in the cylinder. Although I have noticed the car runs very hot even with an mishimoto radiator I wouldn’t think that the brand new MLS headgasket would be blown. Any input or advice would be appreciated. Thanks!

Could be improper valve timing, blown head gasket, bad piston rings, bent valves etc etc.

How did you find that you have leak to crankcase? Did you already run a leakdown test? You can't know if you have leak to crankcase through piston rings by boost leak test or compression test. Some air coming from crankcase while running a boost leak test is normal.

First I would make sure if the valve timing is correct. And if the timing is good, I would run a leakdown test before removing the head, just for in case.

 

[dsm_jeb]

Could be improper valve timing, blown head gasket, bad piston rings, bent valves etc etc.

How did you find that you have leak to crankcase? Did you already run a leakdown test? You can't know if you have leak to crankcase through piston rings by boost leak test or compression test. Some air coming from crankcase while running a boost leak test is normal.

First I would make sure if the valve timing is correct. And if the timing is good, I would run a leakdown test before removing the head, just for in case.

Yes I checked valve timing and all good there. I don’t know what is causing the crankcase boost leak but I know it’s not pcv. The crankcase boost leak seem excessive, it’s the only leak I have left and it leaks down to 0 psi from 30psi in 2 min

Thank you I will run a leak down test once I get the tool and how would I determine the results of that test?

 

[pauleyman]

You keep saying crankcase boost leak. A boost leak is from the intake not the crankcase. Are you saying you have excessive crankcase pressure? What and how are you testing?

 

[dsm_jeb]

You keep saying crankcase boost leak. A boost leak is from the intake not the crankcase. Are you saying you have excessive crankcase pressure? What and how are you testing?

I’m saying when I hook my boost leak tester up to my turbo inlet or my ic inlet I have boost leaking from my pcv fresh air hose and from my oil cap. So I have boost leaking from the combustion chamber into the crankcase via hg, or rings.

 

[DSMPT]

Yes I checked valve timing and all good there. I don’t know what is causing the crankcase boost leak but I know it’s not pcv. The crankcase boost leak seem excessive, it’s the only leak I have left and it leaks down to 0 psi from 30psi in 2 min

I’m saying when I hook my boost leak tester up to my turbo inlet or my ic inlet I have boost leaking from my pcv fresh air hose and from my oil cap. So I have boost leaking from the combustion chamber into the crankcase via hg, or rings.

You can not know the cylinder sealing condition by a boost leak test, that's what Paul and I mentioned above. And while running a boost leak test, it doesn't hold the air pressure forever. The air pressure would drop faster than you imagine and always some air go into crankcase and you will hear that from oil filler cap, pcv holes on valve cover or dip stick tube, that's is normal. This is because you can not close all the intake valves in the same moment if the cams/timing belt are installed. Some cylinders have intake valves open (but exhaust valves are closed to hold the pressure), and then the air go into cylinder and go into crankcase through piston rings. Also if you are applying the air from turbo inlet, also the air go into crankcase through the turbo oil drain pipe. To determine what kind of cylinder sealing issue you have, you need to run at least a leakdown test. Boost leak test is not for that purpose. And compression test won't tell you from where it is leaking.

it leaks down to 0 psi from 30psi in 2 min

To me. it doesn't sound abnormal.

Thank you I will run a leak down test once I get the tool and how would I determine the results of that test?

You can find a lot of how to run a leakdown test videos in google. The point to run a leakdown test, you run the test each cylinder one by one (when the engine is hot would be better), and the cylinder that you are working on must be in the end of compression stroke which means the cylinder has the both side intake/exhaust valves fully closed. Then you apply the compressed air to a cylinder and compare the pressure difference % between the air compressor side and cylinder side. Also you try to hear from where the air is escaping. So you can know if it's leaking from intake port, exhaust port, coolant passage or crankcase.
As you mentioned that wet compression test didn't make much difference, it could be more like the valves are not sealing well rather than piston ring sealing, like a lot of carbon deposit on valves, damaged valves or valve seats etc.

When you run a leakdown test :
Cam dowel position at 12 o'clock = Cylinder #1 has IN/EX valves fully closed.
Cam dowel position at 3 o'clock = Cylinder #3 has IN/EX valves fully closed.
Cam dowel position at 6 o'clock = Cylinder #4 has IN/EX valves fully closed.
Cam dowel position at 9 o'clock = Cylinder #2 has IN/EX valves fully closed.

 

[pauleyman]

I agree with DSMPT. Leakdown is the next step. The leaks you hear sound normal.

 

[dsm_jeb]

You can not know the cylinder sealing condition by a boost leak test, that's what Paul and I mentioned above. And while running a boost leak test, it doesn't hold the air pressure forever. The air pressure would drop faster than you imagine and always some air go into crankcase and you will hear that from oil filler cap, pcv holes on valve cover or dip stick tube, that's is normal. This is because you can not close all the intake valves in the same moment if the cams/timing belt are installed. Some cylinders have intake valves open (but exhaust valves are closed to hold the pressure), and then the air go into cylinder and go into crankcase through piston rings. Also if you are applying the air from turbo inlet, also the air go into crankcase through the turbo oil drain pipe. To determine what kind of cylinder sealing issue you have, you need to run at least a leakdown test. Boost leak test is not for that purpose. And compression test won't tell you from where it is leaking.

To me. it doesn't sound abnormal.

You can find a lot of how to run a leakdown test videos in google. The point to run a leakdown test, you run the test each cylinder one by one (when the engine is hot would be better), and the cylinder that you are working on must be in the end of compression stroke which means the cylinder has the both side intake/exhaust valves fully closed. Then you apply the compressed air to a cylinder and compare the pressure difference % between the air compressor side and cylinder side. Also you try to hear from where the air is escaping. So you can know if it's leaking from intake port, exhaust port, coolant passage or crankcase.
As you mentioned that wet compression test didn't make much difference, it could be more like the valves are not sealing well rather than piston ring sealing, like a lot of carbon deposit on valves, damaged valves or valve seats etc.

When you run a leakdown test :
Cam dowel position at 12 o'clock = Cylinder #1 has IN/EX valves fully closed.
Cam dowel position at 3 o'clock = Cylinder #3 has IN/EX valves fully closed.
Cam dowel position at 6 o'clock = Cylinder #4 has IN/EX valves fully closed.
Cam dowel position at 9 o'clock = Cylinder #2 has IN/EX valves fully closed.

Thank you this will help a lot! Hopefully just needs some new rings. I will post again when I get the tool and test.

 

[DSMPT]

IMO, it would be easier if the issue is the head gasket or valve sealing since it can be done by removing just the head, no need to drop the entire engine or open up the bottom end.

 

[pauleyman]

Was it running well at any time? Rings don't just "go bad". Something else is more likely. What changed? What did you change?