Fuel System Issue

[Gregmy123]

Hi Folks,
I hope you can help me.
Just bought 2006 Baja Sport. 53K miles
It has been sitting in a lot for many years. New battery, Spark Plugs and Oil. Added gas + 2 bottles Sea Foam.
Started up. Got CEL code P0463.
Gas gauge was staying on E.
Replaced Fuel Pump only - on passenger's side and sock/filter.
Replaced Drivers Side Secondary Fuel Level Sending Unit + new filter.
CEL went out.
Runs fine when tank is full.
Fuel gauge now works but:
When gauge drops to 3/4 tank, engine runs like crap like it is about to run out of gas, backfiring but there is plenty in tank.
It had some very old gas in it.
What do you think?
Thanks in advance for any help!
Gregmy123

[FlyByNite]

Fuel filter?

[Gregmy123]

Fuel filter?

This filter is inside of tank - part of Fuel Pump Assembly.
I replaced it when I replaced fuel pump.
But it might have clogged up already from all the crap on bottom of tank that sat for like 10 years. Thanks

[Guacamole]

I'm no mechanic, so here's my 2c:
Did you drain the fuel tank when you changed the pump? I know it's not required as the pump is accessible from the top, but that's decade-old gas we're talking about that likely had ethanol added. The likelihood of that ethanol turning to water is pretty much guaranteed at this point. Plus since water is heavier than gas, it will settle at the bottom of the tank under the gas. When your tank runs low it means the pump is sucking up a higher percentage of water than actual gasoline potentially causing your engine troubles.
Just a thought.

[ZUBAJA]

While I haven't checked my Baja yet (never really thought about it until now), all my other Subarus also have a fuel filter up in the engine compartment. Other possibilities could be any pinched or deteriorated lines in the fuel evaporative system, charcoal canister, etc. Dennis

[kamesama980]

Zubija: Turbos (and IIRC, later NAs) don't have a fuel filter in the engine bay. They only have the in-tank filter.

I'm no mechanic, so here's my 2c:
Did you drain the fuel tank when you changed the pump? I know it's not required as the pump is accessible from the top, but that's decade-old gas we're talking about that likely had ethanol added. The likelihood of that ethanol turning to water is pretty much guaranteed at this point. Plus since water is heavier than gas, it will settle at the bottom of the tank under the gas. When your tank runs low it means the pump is sucking up a higher percentage of water than actual gasoline potentially causing your engine troubles.
Just a thought.

Unless you know a whole lot more about fuel chemistry than I do, ethanol doesn't turn into water. It absorbs water rather than separating (like gas or oil) and creates more water in the combustion process than non-oxygenated fuel but it won't turn to water in the tank.

At 10 years old, the ethanol content is irrelevant, you have garbage in there and it needs to be removed.

Gregmy123: have you tested that it has problems at 3/4 tank (ie, filled it up and it ran fine till it got back down to 3/4 again) or it just started having problems and you happen to have burned 1/4 of the tank so far?

[ZUBAJA]

Unless you know a whole lot more about fuel chemistry than I do, ethanol doesn't turn into water. It absorbs water rather than separating (like gas or oil) and creates more water in the combustion process than non-oxygenated fuel but it won't turn to water in the tank

Not to argue chemistry, water isn't going to turn into fuel, and fuel isn't going to turn into water. That we can agree on. From my experience down here, on a humid day (90% of the 365), you can take a quart of ethanol, pour it into a pan, and watch the surface become cloudy as it absorbs the moisture from the air. You can then cover the pan, come back a day later and there will be water in the bottom of the pan. This is because the water will separate from the fuel. I see so many small equipment failures for just this reason, there will be water in the tank or carb bowl even though the machine has not been left out in rain.
Likewise, especially with ethanol, I have seen fuel that was drained because of a no start and there is no water present. The old fuel however, will not be flammable enough for the engine to run. On these machines, fresh fuel and they crank right up. This is the reason that all my small equipment runs on ethanol free fuel only.
Regarding the OP's problem with running rough after a certain level, I don't think this involves fuel quality. Dennis

[Gregmy123]

I'm no mechanic, so here's my 2c:
Did you drain the fuel tank when you changed the pump? I know it's not required as the pump is accessible from the top, but that's decade-old gas we're talking about that likely had ethanol added. The likelihood of that ethanol turning to water is pretty much guaranteed at this point. Plus since water is heavier than gas, it will settle at the bottom of the tank under the gas. When your tank runs low it means the pump is sucking up a higher percentage of water than actual gasoline potentially causing your engine troubles.
Just a thought.

Did not drain tank.
That was dumb of me.
I am pulling passenger side fuel pump and driver's side
fuel level sending unit.
And cleaning tank. And replacing filters.
And I am doing the Spray Seafoam thru Throttle Body procedure.


Thanks

[Gregmy123]

Zubija: Turbos (and IIRC, later NAs) don't have a fuel filter in the engine bay. They only have the in-tank filter.

I'm no mechanic, so here's my 2c:
Did you drain the fuel tank when you changed the pump? I know it's not required as the pump is accessible from the top, but that's decade-old gas we're talking about that likely had ethanol added. The likelihood of that ethanol turning to water is pretty much guaranteed at this point. Plus since water is heavier than gas, it will settle at the bottom of the tank under the gas. When your tank runs low it means the pump is sucking up a higher percentage of water than actual gasoline potentially causing your engine troubles.
Just a thought.

Unless you know a whole lot more about fuel chemistry than I do, ethanol doesn't turn into water. It absorbs water rather than separating (like gas or oil) and creates more water in the combustion process than non-oxygenated fuel but it won't turn to water in the tank.

At 10 years old, the ethanol content is irrelevant, you have garbage in there and it needs to be removed.

Gregmy123: have you tested that it has problems at 3/4 tank (ie, filled it up and it ran fine till it got back down to 3/4 again) or it just started having problems and you happen to have burned 1/4 of the tank so far?

I think you are correct. Crap at bottom of tank.
And car is running like crap no matter what the fuel level is. I am removing fuel pump assembly and draining/cleaning tank.
Thanks