Crazy problem.

[bulachip]

My car only starts when the gas tank is above 1/2 full or so. If started it will run fine regardless of tank level but if it is shut off it will only start if the tank is nearly full. The only fix seems to be to put in more gas. A gallon or two always does the trick. Any ideas?

[SoCal Driver]

Exorism.

[legion]

New fuel pump?

[bulachip]

But it starts fine when it is full? And it runs well!
Any other ideas?

[Razorback1980]

Check the venting of the gas tank? My guess is that it's not the extra gas fixing the problem, it's the opening of the gas cap. Just a long shot guess though. Where does one find a car exorcist? Might be a good contact to have!

[Tishabet]

Originally posted by Razorback1980
Check the venting of the gas tank? My guess is that it's not the extra gas fixing the problem, it's the opening of the gas cap. Just a long shot guess though. Where does one find a car exorcist? Might be a good contact to have!

This seems like a pretty good possibility to me.

When you say it won't start, you mean the engine is turning over etc but it's not catching, right?

[bulachip]

Yes the engine is turning over but no catch. How do I check the venting? Is there supposed to be a vent in the gas cap or is their a seperate vent?

[bulachip]

I have noticed that when I remove the cap there is always a lot of pressure that comes out

[Eldorado]

actually i think that's the other way around... it's a negative pressure sucking air in..

[SoCal Driver]

Any gas tank that does not vent a bit will colapse into itself like a crushed beer can.

You may have trash floating around in the tank that covers the intake at the bottom when the fuel level is lowered. Pumping fuel into the tank dislodges it or causes it to float a bit higher. Heard of someone having a golf ball in their tank that would do about the same thing.

[Eldorado]

i agree with socal.. could be crud in the tank..
but this doesn't explain why it will stay running after that point...

what happens if you run the car until it's below the half way mark, and you turn the engine off and then immediately back on again.. will it start?

[Razorback1980]

Best thing is to put a fuel pressure gauge on the engine and see what the pressure is when it doesn't start. That will tell you whether you need to search down why the fuel pressure isn't there or not. If you have adequate fuel pressure and it still won't start, then look for what else is suppose to be there but isn't. If you don't have fuel pressure, start working your way back until you find the blockage. Takes four things to make an engine run..fuel, spark, timing and compression....trace down the one that is missing. Still want that exorcist contact though!

[Granite 944]

Get it up on blocks/whatever............drain the tank, pull the tank screen out and look at it, replace/clean if/as needed (I'm betting on it). Change your fuel filter, and get on with life. typical maintenance issue. Do it anyway. You may even wanna pull out the sender unit, so you can look down into the bottom of the tank from above.........just to see the "crap" thats in there, possibly acting like a check valve.

If not it, come on back with your findings AFTER that.

[jezza944]

While we are on this subject, is the cap vented? I have heaps of pressure (or suction) whenever I remove my filler cap. The smell of fuel vapour is really overpowering.

[SoCal Driver]

Gas tanks are supposed to be venting through the charcoal filter. There is a vacuum switch and line set up to scavenge the vapors back into the intake.

[bulachip]

Where is the tank screen located?

[earlr85944]

my moneys on the in tank screen and fuel filter also. and check the inlet screen on the fuel pump while your at it.
the filter unscrews from the tank where the rubber fuel line attaches from it to the fuel pump.