Engine problem - '85 Mercruiser 170

scook

scook

God
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?
 
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.
 
spareparts said:
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.
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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.
 
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
 
Keeping it simple
A engine needs three things to run
Air
Oil
Gas
I would start there check to make sure all those things are good
Just my 2 cents
I could get lucky sometimes, but definitely check your water separator The gas they sell today is not hood e 10
 
Don't forget spark.

Yeah, I agree - need to check for gas in the oil and address all fuel issues. At the beginning of the season, I emptied the tank thoroughly, drove a few extra miles and filled up with non-ethanol gas and thought this was going to be a trouble free season. 30 year old boat, I guess I've got to expect an occasional problem, but I'd rather it wasn't during fishing season.
 
also, if they haven't been replaced recently, replace all your fuel lines, I've been doing that on boats only 5 years old to fix issues. This new fuel whether E or non-E is tough on rubber lines.
 
Hah - Spare, I think you nailed it. I got the boat in '05 because it was doing exactly what it's doing now - ran 20 minutes and died. We changed the fuel line ant it ran OK.

The guy who owned it before me was a complete non-mechanic (knew how to change the oil and that was it). He had lots of money and when he got frustrated with the V-20, he went out and spent $65k on a new 23' Striper WA and told me later that the V was a better boat in the ocean.

They were only going to give him $1700 trade-in for the boat and trailer and he said "no, I love my old boat and I'm not giving it away to a dealer". My daughter did some work for him and got the boat for me for my birthday with the assurance it was going to a good home. I've done a lot of work on it, but I see why he loved his old boat.:clap:
 
Do I need to use USCG approved, below deck fuel line, either because it is required or because it is safer than automotive line? I haven't checked automotive pricing but the approved stuff is around $6/ foot at West Marine.
 
For inboard in engines use A1 rated fuel line. The automotive line isn't approved and won't hold up as well as the marine hose. Look on line, you should be able to get a better price than that. I think I retail it for $3/ft. West marine has good prices on tackle and electronics, but they raape you on everythign else. Even with my Port Supply(comercial side of West Marine) I can beat their prices on engine stuff most anywhere else. Check with Jamestown Distributors or Ebasicpower.com
 
Automotive line also isn't meant to be used under vacuum, and will collapse. Learned this one the hard way. I paid $2.69 a foot for 3/8" marine fuel line from my local hose shop.
 
You guys were right about West Marine prices. ebasic power had the hose for about half - next project, I'll plan ahead and buy smarter. I decided I wanted to get it done last weekend, so I went ahead and let WM thank advantage of me. Got my fishing buddy to help me fish in the new line, changed the fuel/water separator filter and plumbed through the transom to the kicker motor line. Got the line installed with no sharp bends anywhere. A little gas down the carb and it fired right up.

Hoping to sneak out early one morning this week to give it a good trial workout.

Funny thing (it's funny now that it's resolved) when I got it running, I looked down and the volt meter was pegged at zero - this is after just putting on an alternator kit recently. I kidded myself that it could just be the gauge but decided to test it. Not running, the battery voltage was good and running, the charging voltage was good, so it was the gauge. I whacked on the gauge for a while and it came up to a correct reading. Another project to do this winter.
 
Changed the fuel lines - did a careful job - only gentle bends. When I cut the 10 year old hose open, was surprised to find it in good shape - slit it in half, bent it both ways back onto itself - no cracks, loose rubber or anything like that.

Still the same problem - started great & ran great for about 20 minutes and RPM started dropping off. Turned around and headed back - as it started coughing and wanting to die, I pumped the throttle and got a little more out of it. That tells me it must be a fuel problem - right?

I put some air pressure on the fill tube and got nice air flow out of the vent, so I don't see how it could be bad venting causing a vacuum to build up in the tank.

Oil doesn't smell of gas so fuel pump not leaking into crank case but I can't think of anything it could be at this point but the fuel pump???

Before I order a fuel pump, is there anything I'm missing? Remembering back 10 years when I got the boat because it was doing exactly the same thing, I replaced both the fuel lines and the pump before running it and distance, so it could have been the problem then.

Found this pump for a lot less than other prices I've seen - anyone know anything about this supplier or the product? http://www.cpperformance.com/p-23396-fuel-pump-mercruiser-861676a1.aspx It made me a little nervous that for this mechanical pump, the product description said it had solid state electronics and a simple 2-wire connection.
 
scook said:
Changed the fuel lines - did a careful job - only gentle bends. When I cut the 10 year old hose open, was surprised to find it in good shape - slit it in half, bent it both ways back onto itself - no cracks, loose rubber or anything like that.

Still the same problem - started great & ran great for about 20 minutes and RPM started dropping off. Turned around and headed back - as it started coughing and wanting to die, I pumped the throttle and got a little more out of it. That tells me it must be a fuel problem - right?

I put some air pressure on the fill tube and got nice air flow out of the vent, so I don't see how it could be bad venting causing a vacuum to build up in the tank.

Oil doesn't smell of gas so fuel pump not leaking into crank case but I can't think of anything it could be at this point but the fuel pump???

Before I order a fuel pump, is there anything I'm missing? Remembering back 10 years when I got the boat because it was doing exactly the same thing, I replaced both the fuel lines and the pump before running it and distance, so it could have been the problem then.

Found this pump for a lot less than other prices I've seen - anyone know anything about this supplier or the product? http://www.cpperformance.com/p-23396-fuel-pump-mercruiser-861676a1.aspx It made me a little nervous that for this mechanical pump, the product description said it had solid state electronics and a simple 2-wire connection.
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You sure thats the right pump? It says it's for a 3.0L not a 3.7L. ust looked it up and see nthe 2.5L, 3.0L, 3.7L, and I guess the straight 6 all used the same pump. I see IBOATS also has it for about the same price for a sierra, and ebasicpower has a GLM for $129.95.
 
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With people who say a mechanical pump has solid state electronics and, 2-wire connection, I'm not real sure of anything but the Mercruiser part number they start with is the correct one. For a few bucks more, I'll go with a known supplier.

You think I'm on the right track swapping out the fuel pump at this point? Anything I'm missing?
 
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