Mercruiser 3.7 distributor & fuel pump questions

[gw204f]

Thanks again. Mind if I run something else by you?

Checked compression this evening. Cylinders 1 thru 3 were 150 give or take a few. Cylinder 4 only pumped up to 42. I checked it like 6 different time with 2 different gauges.

So, I added a tsp of motor oil to the cyl, rechecked and there was no change. This was the first wet compression test I had ever attempted so I wasn't sure how much oil to use. Been doing some reading since and I don't think I used enough.

Anyway, I ran it again for probably 10 minutes and let it get good and hot. 1, 2 and 3 each came up about 5 psi. 4 came up 50 to 92.

Still not quite sure what all this means. Oil doesn't appear to be contaminated w/ coolant. I did note what looked like some rust on the number 4 plug though.

The longer I let it run, the smoother it got. She definitely loses power when you pull the plug wire to that cyl, so it IS contributing.

Took a few videos of it running.





The oil pressure guage was jumping between 40 and 60.

Any thoughts?

Thanks again for your help.