Mercury 25 4 Stroke. Gas In Oil

[LittleRedFisherman]

Wow, I know I wanted an evinrude when I got that boat, but he was selling those moters at cost so went with it... As far as breaking in, I remember going to the st francis over here, and I ran it like they told me for about 2 hours breaking it in. I don't remember the exact procedure, but the first tank of gas I was trying to break in properly. No water in the oil, but it smells of gas for sure. when I changed it when I first noticed it, a buddy and I fished hard one day, and probably ran it a good couple hours worth. It didn't seem to me that it accumulated any more? I used it again a week later, but didn't check it, was kinda in a hurry and forgot, then it set up for a few weeks till I checked it Friday, and it was full. you think it's possible that there pressure building up in the heat, and forcing gas out that pump, where as the prime bubble can't pump it that tight? Ii'm pretty sure the tank is properly vented tho, plus it has some kind of apperatice on the fuel line that is suppose to keep that form happening as well?

Thanks for your help, i'll try the next procedure and see what happens, otherwise i'll just keep changing oil more frequently till she blows, then get an ETEC..

[bfishn]

Gasoline expands at a rate of 0.058%/degree F, so a tankfull on a 100 degree day that was filled from a ~60 degree underground tank willl increase in volume by 2.32% . The actual pressure developed in a closed (unvented) tank depends entirely on how full it is. A quater tank of gas has lots of vapor space which can be compressed, resulting in relatively low developed pressure. A completely full tank with little or no vapor space to compress is another story, and that seemingly small 2% increase in volume won't be denied. Whether deforming the tank, expanding the hoses, or pushing past the spring tension at the terminal end, it will find somewhere to go.

When I ran the shop for a Honda outboard dealer at the turn of the century, "making oil" was a fairly common problem, but as Wrench noted, those were all carbed engines. I earned a little bonus from the pontoon mfr we repped when I discovered a serial string of boats that had unvented fill stations installed by mistake (they looked exactly like the vented ones). These boats that had 2 strokes merely dribbled a little fuel out the exhaust, the 4 strokes "made oil".

I have no experience with fuelies, but logic dictates that the spring tension on the internal check valve(s) has to be low enough for a diaphragm type pump to easily overcome. Having never had an FI body apart though, there may be a "dead stop" there I'm not aware of.

Mostly, like you, I'm hoping for an easy fix, and a fuel vent fits that bill nicely. :-)

[Ham]

So what would happen if LRF added oil to his gasoline like it was a two stroke instead of a 4 stroke? Would that be enough oil to give the engine the lubrication it needs? Seems like he could drain off the oil from time to time and replace with fresh.

[fishinwrench]

There's really no "dead stop" in a EFI system, fuel circulates through the system via a fuel rail with all unused fuel being directed back to a vapor separator where the high pressure pump and pressure regulator is housed.

The only direct path fuel has to the crankcase in a EFI is through a ruptured pickup pump diaphragm which is fairly common. Or a stuck open injector which would be something that in all of my "projects" through the years I've never seen happen, and if it did the engine would run REALLY BAD if at all (especially a 2-3 cylinder one).

I once heard another tech throw forth the theory that a bad capacitor in the ECM was holding an injector open.....but that makes zero sense as a shorted capacitor (unable to hold voltage) would supply NO trigger voltage to an injector upon demand, leaving it CLOSED at all times... not open. But supposedly he was able to rotate the injector leads and "move the problem" to an opposite injector during a static test. Real head scratcher there !

Nevertheless he swapped the ECM (a pricey gamble) and claims that that "cured it".

[fishinwrench]

So what would happen if LRF added oil to his gasoline like it was a two stroke instead of a 4 stroke? Would that be enough oil to give the engine the lubrication it needs? Seems like he could drain off the oil from time to time and replace with fresh.

It would smoke like a steam engine, foul the plugs immediately on a cold start, generate tons of carbon in the exhaust tuner, throw the fuel pressure regulator and high pressure pump into a real hissy fit, and would fail to help lubricate the crank bearings and valve assembly.

[bfishn]

Thanks for the explanation Wrench.

Of course he claimed the new ECM fixed it. :-) I've got an HVAC tech that likes to replace boards when he can't find the real problem. He has a sizable stash of used boards in his truck, and no explanation why he won't throw them away...

On the other hand, while a shorted cap won't charge or discharge, it will pass the input voltage, as a shorted cap is essentially a piece of wire. No idea what that means for injectors though.

[fishinwrench]

On the other hand, while a shorted cap won't charge or discharge, it will pass the input voltage, as a shorted cap is essentially a piece of wire. No idea what that means for injectors though.

It would "pass it" sure enough.....pass it right to gnd. No ?

It's only 7-9v. Any short to gnd would knock that down to about .02 at the injector I'd think.

I dunno. THAT kinda knowledge doesn't help me one bit so I draw a line as to what gets into my brain and STAYS, and what to boot out in order to have more room for figuring out how to make fish bite.

[fishinwrench]

You think your 4-strokes are quiet now, just wait a bit and they'll get even quieter!

Sorry, I can't NOT throw in a derogatory remark about 4S outboards in general here. It just wouldn't be ME if I didn't.

[bfishn]

I don't know enough about EFIs to discuss it fairly, but the 'killed' voltage would depend on the resistance (or impedance if it's a pulsed signal) of the load (injector?). Ohms law stuff.

Ha! I actually think about that kinda stuff while waiting for a fish to bite. Maybe my ex was right...

[fishinwrench]

Well you just Rock at multitasking.

If you were to call me with a "tech question" when I'm out fishing, or on my way fishing....there's a good chance I won't even be able to tell you what color Mercury outboards are.

My worst fear is having my outboard fail to start when I'm out fishing and not knowing how to fix it.

Only SLIGHTLY exaggerating.