bad gasoline? (not!)

[JD1964]

Edit: this thread has morphed into other than bad gas but if you're interested in the saga, read on

We went to put gas in the wagon with LT1 engine. It was close to empty. It ran perfect on the way to the gas station. We put in $50 of 93 octane. Literally 15 seconds after starting it back up it developed a stumble. It continued to stumble on the way home and got gradually worse.

Did some typical diagnostic work to rule other things out and couldn’t find anything wrong. Took a sample in a glass jar and compared it to other 93 octane I had and the suspected bad gas was slightly more yellowish in color. Drained all the gas out of the wagon tank. Took a risk and put 5 gallons of the suspected bad gas in my transit work van with 4 cylinder engine. It was low on gas too. It took the gas and ran fine with no missing of any kind.

Went and got 5 gallons of 93 octane from a different gas station and put it in the wagon. I need to run it longer to be sure but had to come in for the evening. Ill run it more tomorrow. Anyway, the wagon LT1 ran good again with this other gas, at least initially.

Is it possible that the suspected bad gas was “borderline” and the LT1 didnt like it but the 4 banger transit had no problem with it?

 

[DRIVEN]

What wad the ethanol blend? E10? E15?

 

[JD1964]

What wad the ethanol blend? E10? E15?

I’m not sure exactly. Some of the pumps around here say “may contain” and then list either 10 or 15%. So how do you ever really know for sure?

 

[Built6spdMCSS]

If the car sat for a bit, you stirred up some moisture in the tank and it went into the engine. Add some HEET.

 

[Ernest]

Automotive gremlins, gotta love'm.... did you possibly feed(gas up) your engine after midnight?

Electric fuel pump issue perhaps... you're not supposed to run with less than 1/4 tank or near empty, the fuel keeps the pump cool, possibly over heated and damaged, check the fuel pressure and do a leak down test.

 

[Clone TIE Pilot]

If your tank was low you might have sucked some gunk into the fuel or when you added gas it stirred up the gunk and got injested by the fuel system. Either way it would be a good idea to replace the fuel filter.

 

[JD1964]

The engine swap is recent and the tank had been removed , cleaned and inspected. It’s spotless inside. At first I suspected water so I let it sit for 2 days to allow any water to settle to the bottom. Then I took about a quart of gas into a glass jar directly from the fuel line at the rail by cycling the key using the priming event that the PCM controls. Not a single drop of water or other debris in the sample.

The pump was new with the recent swap. I understand repeatedly running low on gas can damage the pump but that is not the case here I’m pretty sure. This pump has not been in service long enough to be subjected to that condition.

Nonetheless, during my diagnostic efforts I put a pressure gauge on the rail and the pressure is exactly where it should be for the LT1. That includes both vacuum line connected and disconnected.

So, no problem with fuel delivery or pressure.

I connected my laptop with EEhack program and there are no stored or pending DTC’s. All sensors are behaving normally.

 

[JD1964]

Alright, after changing the gas it’s still missing. It’s actually doing the same thing it had done when I was first tuning it after the swap. I’ll have to go back and search my various forum posts to see what I had done to sort it out. Maybe the valves came out of adjustment. I hear some tapping at hot idle. Possible vacuum leaks also maybe. I think next I’ll check the valve adjustment. I’ll post back with what I find.

 

[Ernest]

I see noone mentioning checking spark plugs... could be one or more out of the bunch that suddenly went bad.

 

[JD1964]

Here’s a video of the hot idle stumble in gear.