Bad (old) gas in car?

Tiny
STRICTLYDIMES
  • MEMBER
  • 2006 LINCOLN TOWN CAR
  • 4.6L
  • V8
  • 2WD
  • AUTOMATIC
  • 80,000 MILES
Car was sitting a while. But started periodically. One day it wouldn’t start.
It was a bad fuel pump. Changed fuel pump and car ran great. Also changed Fuel filter and fuel pressure regulator, as a precaution. The next day it ran very rough, after idling for two hours it was somewhat better, but still not smooth.

When I power brake it, you can hear the motor dieseling.

Gas does smell old.

It has about 1/4 of a tank.

Added some dry gas (Heet) to it.

I assume I have to siphon the old gas out but would rather let it run it almost empty and put some fresh gas in it.

What about sea foam treatment or similar?

Thoughts?

Thanks
Monday, July 24th, 2023 AT 11:08 PM

3 Replies

Tiny
STEVE W.
  • MECHANIC
  • 13,207 POSTS
The easiest solution would be to use the pump to pull the old gas out of the tank, put it in a gas can and use it in a mower or dispose of it. If it has ethanol in the fuel that likely has separated out and that is causing the problems as even the flex fuel engines don't like straight booze. To do that you just remove the fuel line from the fuel rail and attach a hose to direct the fuel away from the engine. Then go to the pump and connect power to it, Unplug the power connector and connect battery positive to the terminal (7) that had the pink w/ black wire and ground to terminal6 that has the brown w/white wire. Let it pump until it's dry. Now add in new fuel and let that run a bit to purge the line and filter. Now connect the fuel line back up and start it. The fresh gas should push the old stuff out of the injectors rather quickly.
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Tuesday, July 25th, 2023 AT 6:17 PM
Tiny
STRICTLYDIMES
  • MEMBER
  • 14 POSTS
Hi, thanks for the reply. I will give this a try. In your opinion, do you think I did damage to a) the engine and b) the fuel pump by idling the car and gently increasing rpm’s occasionally for about 2 hours? I thought it would clear itself out by doing this.
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Tuesday, July 25th, 2023 AT 7:45 PM
Tiny
STEVE W.
  • MECHANIC
  • 13,207 POSTS
It shouldn't have done any real damage. I would however flush it, then start it just long enough to get it warm and change the oil just to remove any contaminants that may be in it. I would expect it to start a bit hard and then clear out as the new fuel gets run through. If there was anything in the lines you might get an injector related misfire but those are not bad to change out if needed.
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Tuesday, July 25th, 2023 AT 8:10 PM

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