Engine problem - '85 Mercruiser 170

scook · #1 08-17-2015, 06:13 AM

Pertronix electronic ignition last year - starts and runs great (for a while).

Early June ran at approx. 3000 RPM for around 15-20 minutes, ran near idle for a few more minutes before anchoring up to fish - no problems. Maybe a half hour later tried to start up to move a little, idled very rough, wouldn't run up above idle (not in gear - no load). Tried a few times to start again over next hour or two, best it would do is very rough idle, wouldn't run up at all and died.

Yesterday, started with a little gas poured in carb (hadn't been run since Early June), idled and ran great, ran at approx. 3100 RPM for around 20 minutes and noticed RPM's very slowly decreasing, took it down to idle, it got rough and died almost immediately. At idle the oil pressure dropped to near zero - checked oil and it is good. Didn't try to restart - another long trip back on the outboard trolling motor.

Water temp in the river is around 70 degrees if that helps any.

It's got me stumped. Anyone have any ideas?

smokeonthewater · #2 08-17-2015, 10:13 AM

Sounds like it may be a fuel problem

bradford · #3 08-17-2015, 01:22 PM

Agree with Smoke. Sounds like fuel and possibly water in the fuel.

spareparts · #4 08-17-2015, 06:47 PM

does your oil smell like gas? Could be a bad fuel pump leaking gas into the engine, that will make your oil pressure very low and at teh same time cause a fuel delivery issue.

THEFERMANATOR · #5 08-17-2015, 09:14 PM

Quote:

Originally Posted by spareparts

does your oil smell like gas? Could be a bad fuel pump leaking gas into the engine, that will make your oil pressure very low and at teh same time cause a fuel delivery issue.

This is what I was thinking as well. Neighbor went through this on his 4.3L. They didn't put but a small filter after the pump, and it quickly plugged up with rubber from the pump. His carb plugged up, engine would barely idle, and his oil pressure dropped like a rock after a gallon of gas went into the crankcase.

scook · #6 08-17-2015, 11:31 PM

I'll do some oil sniffing. Probably should change the fuel water separator filter to be sure it's not water (the tank is full so shouldn't be condensing moisture). I wouldn't think it would start and run great for 20 minutes if the carb was clogged up - this is the second time it's done this. Was leaning toward ignition since it's the only thing that's changed but will work the fuel issues first.

Thanks