87 Nissan Sentra, newer fuel pump & filter. Note: (mechanical pump located on the block & not the tank). Filter can be full until driven a few miles out on the highway, but when returning the fuel in the filter seems to be driven way down and almost empty. That is where the problems begin.
I watch the fuel inside the filter and start to see air pockets along with the fuel being pulled to the line towards the pump. Could I have a clogged fuel line between the filter and tank? a bad cross valve near the tank? or just a bad filter? It seems as if fuel is being pulled from the filter, yet the filter itself isn't drawing so much fuel from the tank.
I haven't heard this one before.
First thought would be air sucking into the line from a cracked hose or bad/ rusty connection.
Secondly, maybe a clogged return line?
Or, maybe a rusty gas tank and/or poor seal on the gas cap?
Yeah, that is pretty normal if the car is not running at the time.
Try removing the gas cap with the car idling and then look at the filter to see if there is a difference.
Ive seen this prob once before and it was due to a crack in the main feed line to the fuel filter, but in your case I think its different...
If I understood you correctly, you mentioned that theres vacuum in the fuel thank.
This should not be!
Let me use an example...
Sipping some liquid out a bottle with a straw.
As you sip, the liquid in the bottle drops.
As the liquid in the bottle drops, air comes into the bottle at the same rate.
If you somehow seal the bottle, preventing air from getting in, it would be difficult to sip up the liquid due to an air-lock situation
I suspect a similar thing happening with your fuel thank.
A fuel thank has a breather pipe attached in conjunction with the filler pipe to allow for air displacement during filling, expansion and contraction, and fuel level drop.
This may be blocked!
What could be happening is, as the fuel pump tries to suck fuel, it eventually encounters the air lock mentioned above.
As this air lock increases, fuel flow diminishes, and the vacuum created tries to equalise itself by sucking air from wherever it can.
Hence the bubbles you see in the filter.
Since my last post my car had been running better than ever! I changed the fuel filter again for a last ditch effort and the car ran for at least 5 days of 60 mile round trips to and from work. The moment that I changed the filter, it filled up with fuel completely, and I also decided to run unleaded plus gasoline.
Last night I stopped for gas, and decided to try running regular unleaded once again. Driving to work everything was fine, but my trip back I found myself back where I started with the car starving for gas again. All I can figure is that I have dirt in the tank and its clogging up the filter, or I've been getting some bad gasoline. The car ran strong and better than ever for a good 5 days, and I was convinced that it was fixed.
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