[gearyg]

A few weeks ago I was running at aroung 3,000 to 3,500 RPM looking for the bait receiver. I heard my alarm going off, (not sure how long it was sounding as I had my head in the wind and could not hear it until I brought my head in the console). I looked back and saw alot of white smoke (maybe steam) coming from the port just below the cowling in the rear. I tilted the engine up and saw a plastic bag floating away. I shut it down for about 10-15min and then after starting it again, everything seemed ok.

About a week later, I decided to do a compression test. Numbers 1-3 were around 175psi and number 4 was 90psi. I did several tests and they were the same. I then squirted some oil in number 4 and the psi came up to 175. I then started the engine for about 5min. A week later, I did another compression test and all 4 cylinders were 175psi, 1st, 2nd and 3rd test. Not sure what could cause the....any advise? Do these engines hic-up like this...kind of wierd, not sure what I should do.

The only thing I did on the second test is that my oil was on the low side, so I added about 3/4 qrt of oil.

[rodbolt]

dunno, actually I cant recall ever running a compression test on an F115. I always use a leakdown test cause its so much quicker and more accurate.
I would wait a bit and try it one more time with engine warm and throttles fully open and all plugs removed.
ALWAYS remember to pull the stop lanyard when runing a compresion test on that motor.

[gearyg]

I think I am going to take it in to get a leakdown test done, I don't have the equipment. I am wondering if it is low on oil, could this have anything to do with it. It is just really wierd that I could even get a 90psi reading out of cyl #4. I can understand that it will increase my psi once I squirt some oil in the cylinder, but that should dissipate once I idle the engine for a few minutes and it sits for a week correct? I am baffled, and would hate to take it to a dealer and have them do a teardown when it is not necessary...it is alot of money.

Question, I did my compression test as you mentioned above, but why is it so important to "Remove the Lanyard" when cranking the engine over. If all the plugs are removed, it can't start anyway correct?

[rodbolt]

without removing the stop lanyard you will have to disable the ign AND fuel systems.
otherwise you may have sparks AND a chemically correct Air/Fuel mix blowing out the plug holes.
the fire ball can be funny .
with the lanyard removed it disables both ign and fuel systems. you will get an alarm when cranking with the lanyard removed so it tests the horn as well.
I watched some guys light up a 150 mariner oneday. just after I warned them and they looked at me like I was stupid, so I walked away to watch the show
and that is why with EFI the ign AND fuel systems need to be disabled when running a compression test
however a leakdown is just to quick and easy and I only have to rotate the flywheel 4 times by hand 180* at a time.
1&4 will be at TDC,only one will be on compression stroke,180* and 2&3 will be at TDC with only one at compression stroke,another 180 and 1&4 are back at TDC check the one that was not on compression stroke the last time, another 180 and your back to 2 or 3 .
no cranking no muss no fuss and if its bad I know what is leaking and where.

[gearyg]

Thanks for the info, I will definately remember the Lanyard thing. I naturally did not connect it when doing a compression test, but had no idea of the reprocussions if I did connect it. I will update once I get the results of the leakdown test.....