Bonehead move on my part (somewhat long)

[mslim]

I had to drain about 3 gallons of non ethanol 91 octane out of my motorcycle when I put it up for the winter. I had a great old non-EPA Eagle gas can that I used to use to recycle motor oil until the California authorities decreed that they would only accept used motor oil in a black container going forward. I didn't want to dump the gas. That seemed pretty irresponsible so I put it in my '04 4R with about 15 gallons of regular 10% ethanol 87 octane gas. A lot of gas and a little bit of oil should be soluble right?

The car ran as normal so I thought "no harm, no foul". Later as I was getting ready to fill up the Eagle can with 91 for the bike, I shone a flashlight inside and still saw a coating of black motor oil inside. I went to the local gas station and bought 3 gallons of 91 octane again and dumped it into the 4R tank. It ran OK for a while but as the gas level dropped to 2/3 or 3/4 the car started surging. If I put my foot in it it really hesitated. It was almost like a knock sensor retarding the timing. The engine never backfired and I never got a CEL. It would idle smoothly at a stoplight. It got so bad that I was a hazard to traffic so after about 70 miles into the tank I pulled into a Shell station and topped off with 91 octane. I repeated this scenario several times hoping to dilute the amount of residual oil in the gas tank. I even dumped a can of Seafoam into the tank hoping to keep the injectors clean.

I'm pretty sure I've put 20-30 gallons of 91 thru the tank since my bonehead move. The car is running fairly good and I can maintain 70 on the highway OK and when I put my foot in it the V8 does its best "Crown Vic Interceptor" impression but I can make it flat spot if I let it downshift and keep my foot in it.

Going forward I am perplexed about what my strategy should be do alleviate my bonehead move. Mass airflow cleaner? New spark plugs? Marvel Mystery oil? New fuel pump?

 

[AuSeeker]

How much oil do you figure got into the gas?

If just a few ounces I don't think you're going to have too much of a long term issue, as you stated it is running better now and I think it will sort itself out over the next few tanks of gas.

If it was a half to a full quart of oil then the issues may persist for bit, in this case time and even a few more tanks of gas may still solve the issues, adding some more injector cleaner would help even maybe a couple of more times, I would inspect and if needed replace the plugs at some point after it seems to clear up a bit.

 

[mslim]

Hard to say how much oil. It wasn't any oil that you could pour out, just the film left by the viscosity of the oil on the inner surface of the gas can. New plugs wouldn't be a problem, I've done those before. I just didn't want to have drop the gas tank and maybe replace the fuel pump.

 

[AuSeeker]

Hard to say how much oil. It wasn't any oil that you could pour out, just the film left by the viscosity of the oil on the inner surface of the gas can. New plugs wouldn't be a problem, I've done those before. I just didn't want to have drop the gas tank and maybe replace the fuel pump.

I don't think that dropping the tank will be necessary, it should work itself out over time and a few more tanks of gas, the plugs if fairly new should also be fine but I would still pull them and inspect them for any fouling and replace if needed, if they are fairly old then I would just go ahead and replace them but wait it out a while for the system to clear most if not all of the oil out first, oil after all is a petroleum product and it will dilute in the gas and be burned in the engine with little to no ill affects in the long run.

 

[Legender]

Sounds like it seems to be firing OK as you've not had any lights/codes come on. I'd keep running some seafoam through there. Chance the thicker oil may have messed with an injector or two. Might not hurt to remove and clean the rails/injectors just to be on the safe side. Depending on how many miles, might just be good preventative maintenance. You can also look at the plugs and see if they're fouling differently than normal as stated above.

 

[nevada]

it sounds more like there was some water in that fuel.

many years ago I had a failing fuel pump, I thought, "to help it live long enough to afford to replace it.." I would dump engine oil into the fuel tank to help lube the pump. 15ish gallons of fuel and a half quart of oil, no big deal. I never noticed anything. no extra smoke, no strange running.

I doubt some oil residue would cause your issue, but a bit of water for sure would.

 

[mslim]

Thanks to all who have posted. Some food for thought there.

One more data point to consider that I realized today... When the tank gets down to 3/4 full, the "missing" or surging becomes more pronounced. It seems when I top the tank off again it mostly disappears. At first I thought that it improved as I was diluting whatever oil was in the tank and raising the combined octane so that the knock sensor wouldn't kick in.

Now I am wondering if it is a fouled fuel pump pickup or fuel filter or a strata of water or something in the gas tank?? Just to make sure that I didn't have any buried error codes I hooked up my OBD II and made two new scans. Still 0 errors and no CEL at all.

If the fuel pump and filter were accessible through the floorboards, I'd probably pull them and take a look at what's in the tank but I'm 71 y/o and don't feel up to dropping the tank to check the pump and filter.

Any ideas? I know from checking aircraft fuel sumps water is heavier than avgas and sinks to the bottom. Is fuel contamination the most likely scenario?

 

[Seymore Butts]

The fuel pump gets gas from the bottom of the tank, so if your problem was water, it would be evident regardless of fuel level.

I think the only way to deal with contaminated fuel is to flush the fuel lines, flush the tank and inspect or replace the fuel pump. I'd look for evidence of damaged fuel injectors as well.

 

[mslim]

and the rest of the story...

So others can learn from my mistake, here's the final chapter to Bonehead Move.

As AuSeeker predicted, the problem resolved itself after several tankfuls of clean gas. I was getting worried after two tankfuls didn't resolve the problem. I kept adding 91 octane after every 80-100 miles to keep diluting the oil and hopefully raising the cumulative octane in the tank. The missing (or retarded timing) has completely ceased and the V8 has its old pep and power. The sparkplugs don't seem to be affected. I'm confident enough in the car to take it on a 200 mile round trip to Costco next week for new tires.