Gasoline/ahol question

[Rickysa]

First off, I'm happy to display my ignorance in public .

I've been so impressed with the results in using corn-free gas in all of my 2-cycle stuff (and really happy with the '90 carbed jeep rebuild) that I thought I'd try a tank in the pcar. Octane, of course, was lower (89...93 premium), and now I have about 2 seconds of dieseling at shut off. How come?

[red-beard]

Bad anti-dieseling solenoid?

[red-beard]

Lower octane is allowing the higher compression engine to compression ignite.

[sammyg2]

The injectors should close completely as soon as the key is turned off. No fuel, no dieseling.

But if one or more of the injectors leaks and allows fuel to keep getting into the combustion chamber until the pressure in the fuel rail bleeds off, that would explain it.

if that's the case you need to get it fixed regardless of which fuel you use.

Gas in the oil is bad, M'key?

[Rickysa]

I know this experiment has sample size n = 1, but the engine is a complete rebuild and has operated brilliantly over 500+ miles, until this one fuel change. So the (I'm guessing) slight difference in octane would lead to this? I feel pretty sure that a shot of octane boost might remedy the situation, I was just curious as to the mechanical cause.

Thanks for the feedback

[wdfifteen]

Originally Posted by red-beard

Lower octane is allowing the higher compression engine to compression ignite.

This. Your engine needs the higher ignition temps of the the 93 octane to prevent pre-ignition and dieseling. The dieseling is only the symptom you hear, too-low octane fuel increases engine temps and wear and tear at all running speeds. It's ironic I know, but fuel that ignites at a lower temperature (89 octane) makes the engine run hotter than fuel that ignites at a higher temp (93 octane). If gasohol is the only 93 octane fuel available, then use it. It's better for an engine that requires 93 octane than using 89 octane pure gas.
BTW my Stihl dealer recommends the the highest octane available at the pump for the 2 cycle equipment he has sold me (in the past 5 years). They are built for high octane gasohol and run best on it. That doesn't speak for older 2 cycles with soft fuel system parts that might be damaged by ethanol.

[Charles Freeborn]

we can find 92 clear all day around here. Try pure-gas.com

[GH85Carrera]

You 88 911 was designed to run on premium. It is in the owner's manual. There is NO knock sensor of any kind. The engine will indeed hole a piston if you drive with a heavy foot. Unless the rebuild was done to lower the compression ratio. You may will be fine with lower grade fuel, but it is NOT want the engineers designed for your car.

[sammyg2]

My wife sometimes asks me a question and when I answer she says, no that's not it.



Engines do not run without fuel. For an engine to diesel after it is shut off, it needs a continued source of fuel (and source of ignition).

Back in the olden days some carbureted cars would diesel after getting shut off because the fuel in the float bowls would boil and over-flow into the manifold, or the float level was set to high to begin with.

No matter how well your car was running before, there was a symptom that was covered up by the higher octane fuel and uncovered by the lower octane fuel.
An injector can work just fine during operation and still leak when shut off.

You can switch back to the higher octane and ignore the problem or fix it.
But a leaking injector can eventually dilute the oil with gasoline.

If i were you and you're glad I'm not, I'd dump a bottle of techron in the tank and see if that makes and difference.

[Fast Freddy 944]

What's Ahol?

[Deschodt]

Pure-gas lists almost zero ethanol free gas in Cali... Or close to it. Zero in the Bay area, it's nuts. Was hoping our new twitter in chief might have an irrational hatred of Ethanol (on the same level as his other phobias), but seems it's the opposite, so we're screwed... In fairness though, I have never noticed any ethanol derived issues in my oldies... Only in 2 stroke garden tools...

[GH85Carrera]

The farm lobby in the corn states is powerful. We will be burning food for fuel for many years to come. As soon as the special federal subsidizes for growing and producing it is stopped and they have to produces at a profit to survive, it will be over.

[flipper35]

In WI Kwik trip sells 93 octane as pure gas and the lower as e10. Iowa state law requires two of the octane levels to be e10 so some have 87 octane for sale as pure gas and e10. It is about $0.30 difference in price right now. I get all my gas for the Cobra and lawn equipment at Kwik Trip.

[Rickysa]

Sammy...never thought that I'd uncovered a hidden problem, thanks for the heads-up

No 91/93 pure around here, sadly, so tectron to finish this tank and back to premium corn-gas

[KNS]

I add a little bit of Lucas Ethanol Treatment (the green stuff) occasionally to the tank to combat ETOH issues. Finding pure gas in AZ is next to impossible unless you're buying some race gas and that website is usually out of date.

[red-beard]

Rick, look around, you might find some octane boost.

[red-beard]

5 Best Octane Boosters and Additives 2016 - MyCarNeedsThis

[Por_sha911]

Originally Posted by GH85Carrera

The farm lobby in the corn states is powerful. We will be burning food for fuel for many years to come. As soon as the special federal subsidizes for growing and producing it is stopped and they have to produces at a profit to survive, it will be over.

Paging the POTUS...