Low compression

[SuperSam]

I have a dilemma for y’all. So second time out on the lake this year and we had just been idling from the boat launch gave the boat a little throttle and hear a sound that sounds like rushing air or a hose pulled off the engine and the engine immediately starts to run really rough. I immediately shut it down and looked to see if any hoses came loose but none did. Attempted to restart and again was running really rough. For fear of a blown head gasket or cylinder I shut down right away again and get towed in. Checked compression on all cylinders and here is what I have found.IMG_1856.jpg

Please advise on next steps it is a 2005 Tige 22v with the marine power 5.7 340 hp. I am learning to be very mechanical but don’t have experience tearing apart engines but will if I have too...


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[chpthril]

Is that 3 or 6? Not sure if thats front or rear of engine or boat.

125 is low, but not catastrophic. Next step is to do a leak down test. it will tell you where the air is going. Rings, head gasket, valves, block etc.

[gumby]

agree leak down is where it is at. Especially if you used a push in compression tester.

[SuperSam]

Is that 3 or 6? Not sure if thats front or rear of engine or boat.

125 is low, but not catastrophic. Next step is to do a leak down test. it will tell you where the air is going. Rings, head gasket, valves, block etc.

I marked Front of the boat so rear of the engine...good catch I should have clarified that...


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[SuperSam]

Would you guys think that the rushing sound of air could be the sound of air being forced out of the low cylinder? Could the low cylinder not even be the culprit for the noise and the rough running? Would there be any concern to run the engine to try and identify the sound... I don’t think it could be a head gasket or anything like that since no water is in the oil which was my first concern to avoid running it.


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[JCP]

The rushing air sound is not coming from air being forced out of the low cylinder. Try to run the engine again and identify the source of the noise. Run it above idle in neutral if needed to keep it running while diagnosing.

[cbath]

Low compression

I would suggest checking your fuel pressure. Low fuel pressure can cause the symptoms you are describing and as the throttle body tries to compensate it creates a louder than normal intake noise... for lack of a better way to describe. Specs for compression on that engine should be no cylinder lower than 100psi and lowest cylinder not less than 70% of highest cylinder. You have 1 cylinder that is close to that spec, but I’ve seen those engines run fine at 100 psi in a cylinder.


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[SuperSam]

Quick update decided to change out my plugs and put everything back together to see if I could identify where the noise was coming from. Started it up and all was normal. I dropped the boat in and drove around for 30min and had no issues so hopefully it was just a spark plug that had failed that is now replaced. Fuel pressure was checked at the beginning of the season and held at 50psi running I believe. If it starts running rough again I will try and check the pressure while it’s happening to confirm fuel issue but I’m hoping we won’t need to.


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[chpthril]

Spark plugs do not effect compression, so unless that low cylinder was an anomaly, its still low. Did you by chance run a check on the low cylinder a 2nd tim just to make sure it was not a gauge issue the 1st time?

125 psi is 27% lower then the highest. Thats an issue.

[SuperSam]

Spark plugs do not effect compression, so unless that low cylinder was an anomaly, its still low. Did you by chance run a check on the low cylinder a 2nd tim just to make sure it was not a gauge issue the 1st time?

125 psi is 27% lower then the highest. Thats an issue.

I will look at doing it again and possibly a leak down test this week. I feel that I hopefully fixed the problem that presented itself... I don’t think my compression was the reason it was running bad. It doesn’t seem to have any lack of power or any issues so i might be inclined to just leave that cylinder until I’m ready to do a rebuild unless you would think that would cause more issues.

On a side note with a raw water cooled system is it normal for the temp gauge to be right around 175 all the time it will bounce up to 180 at the hottest and drops to around 165 at the lowest. It usually stays right at 175 though. I was looking at the manual and it said 143 thermostat and I am guessing mine has to be the 160 or 165. Do I need to worry about this??? I thought I read somewhere that it is a pretty normal temp but maybe that is for the freshwater cooled ones.


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