4.3 mercruiser power loss

Billy-bob · Jun 17, 2019

Hi all, I need help knowing where to look! I had a total lose of power yesterday. was cruising along then slowly lost revs. first it would restart but stall when in gear, then it wouldn't even start. I had replaced cap, sensor, rotor wares etc. we did have a problem after all the replacement getting spark. A friend mechanic (not sure what he did) but jumped the ignition module to wake it up and it ran well. took it on the water the next week, no issue, then took it out yesterday, ran no issue for about 30 mins. Anchored for about 30 mins, then heading home was when the issue started. I did have water in the tank, I thought I got rid of it, maybe not? Just not sure how to pinpoint the problem. Ignition module isn't cheap so I don't want to go there unless I need to. If it is water in the gas, I am also unsure how to completely drain the tank. HELP!

zellerj · Jun 17, 2019

I don't know what your gas tank configuration looks like, but all boat manufacturers are required to make the tank accessible for inspection. After uncovering the tank, you will probably find a gauge sender fitting that has a number of screws in a circular pattern, Remove that sender fitting, stick a hose in the tank, and suck out the gas from the lowest corner. Examine what you suck out for water separation. I use an oil extraction can with a vacuum air pump. If the tank is aluminum, water in the tank can corrode and cause pin holes to form, so pump out all of the gas and examine the tank for corrosion. Plastic tanks do not have this issue. Keep sucking out gas until all of the water is out by evidence of no phase separation. Also check your gas cap O ring - most water gets into gas tanks on boats because of an old and cracked O ring.

Billy-bob · Jun 17, 2019

do you think it sounds like a water problem. Yes I think it is my first place to look, just wonder what else could be going on. Idle speed was also hardly keeping it going after the lose of power, where just mins before it ran just fine