fuel delivery issue at less than half tank

[Bavarianhoarder]

Hello all,

I will preface by saying I searched diligently for an answer via google and the search function on this board.

I am trying to settle my new 1976 2002 and work out some bugs and the next on my list is that when the car has a half tank of gas or less, it does not enjoy running. At all.

At this point, if the car is parked at all facing down a hill, it has great difficulty starting and I usually have to roll it to level ground. I am able to get about 6-8 gallons of gas into the tank when it reads around half, for the record.

I am going to ohm out the sending unit tomorrow as per instructions I found regarding other F.S.U. issues and see if it is not calibrated or something.

Is there perhaps a fuel pick-up tube that is not long enough or something simple like that?

Any help is greatly appreciated!

Thanks!

[Colin]

Did you check the easy stuff first like is the fuel filter clean? There is a screen on the pickup in the tank that may need cleaning as well. You can also drain the tank to get the crud out. If the car hans't been driven much, the tank can really be a mess!

[Guest Anonymous]

This can happen on the later cars with evap systems, if the fuel tank vent system gets plugged up. The fuel pump will pull some gas out of the tank until there is too much vacuum to overcome then that's it "no more fuel".

Also small cracks in the rubber lines, that are very hard to see with the braided cover that BMW uses, can do basically the same thing. The cracks will let in air (but not leak fuel) which makes the pump lose it's prime....

Dave_Ganzer

[Guest Anonymous]

your idea about a too short fuel pick-up tube might be worth checking out. You need to pull the tube anyway, to see if the screen is clean, so measure it then. On earlier cars there are differnt length tubes for different sized tanks (I think 2002 vz. tii).

[Bavarianhoarder]

Thanks for the replies, guys!

I planned ahead with this post so that when I tackle the issue initially (this weekend perhaps) I would have a head start as to where to begin.

I will report back with my findings, keep the wheels turning in the mean time!

Thanks!!!

[adawil2002]

Advise cleaning the in tank screen and replacing the fuel lines and filter. Can use a siphon to vacuum the scale from the bottom of the tank, filter the crud and reuse the gas.

[TobyB]

I vote air's getting into the suction side of the pump somehow...

t

[Bavarianhoarder]

Hello all,

For the third time in as many weeks, I had this problem repeat itself. Tonight I was within sight of the trusty petrol station when I apparently went below the point of safe return.

I took the fuel sender out while I waited for a local friend to arrive with a gas can, and it appeared at a quick glance that there was just about exactly a half tank remaining. When I refueled, it accepted about 6.5-7 gallons.

I was able to get it re-primed by running the engine on starting fluid for a minute and then once again everything returned back to normal.

The fuel sending unit appears to be in good shape, although it is remarkably easy to turn and thus remove it. For good measure, I have a replacement O-ring for it coming in my next pelican order with a slew of other maintenance items.

I think it seems wise to upgrade to an electric fuel pump regardless, but is anyone convinced that maybe the mechanical one is just mysteriously not up to the challenge?

As mentioned before, all soft lines in engine bay are new, carb was just rebuilt very thoroughly, fuel pump is pretty darn new and upon inspection the diaphragm is in fine shape.

thoughts are always appreciated

[Colin]

Did you drain and clean the tank yet?

[Bavarianhoarder]

I have not drained the tank yet, but I agree that is certainly a great idea.

When I had the sender out, the tank appeared to be remarkably clean.

Is the best method for draining/maintenance to simply remove it?

[Colin]

I have not drained the tank yet, but I agree that is certainly a great idea.

When I had the sender out, the tank appeared to be remarkably clean.

Is the best method for draining/maintenance to simply remove it?

There is a drain at the bottom, actually. Mine looked clean from the sender hole but when I drained it all kinds of crud came out!

[eurotrash]

+1 ^^

I had the same issue when I first got my car, and always on longer commutes. Turned out to be either a weak pump, or sediment packing the screen full as the tank ran down, or both.

The filter (at the firewall) would be dry when it happened. And then after sitting a while, there would magically be fuel in the filter. I believe that the sediment clogging the screen, stalling the car, would fall away as pressure bled off and fuel would get pulled up the line. But in turn, the clogging weakened the pump over time and the car, accordingly, became more susceptible.

Draining the tank, as mentioned above, will eliminate a major culprit in these situations. And should always be the first step. Then, if it persists, throw on a good used pump and see if that takes care of it.

In regards to electric pumps, you'll find its about 50/50 yea and nea from the crowd. But if you go that route, you need to hold the pressure to 3-4 lbs. for a carb, IIRC.

[jgerock]

This can also happen if your fuel lines are old and cracked, allowing air to be pulled into the line from the tank by the engine-mounted pump.

Very frustrating - just ask Marc Caden and his patient wife Stephanie during their Vintage trip this year.

[Bavarianhoarder]

Bummer, my tank does not have a drain plug.

The fuel pump was said to be recently replaced by the p/o, and it looks more or less brand new.

When I had the sending unit out, its' screen was fairly clean surprisingly.

What is the best way to empty/clean a tank without a drain plug, by removing the tank?

[Zenon]

+100 on checking for proper venting. One clue is if you get a sucking sound when you remove the gas cap. Your symptoms sound exactly like what I have observed with a plugged vent (done by a PO that didn't understand).

It needs to be vented such that there should not be any pressure - negative or positive - in the tank, ever.

Replace ALL of the rubber fuel hoses as a matter of course on a new-to-you '02. You don't need fancy hose - garden variety low-pressure fuel line is adequate for a carbed car. About 10 feet of 5/16" ID should do it, with about 1 ft of 1/4" ID for the segment from the mechanical pump to the carb, IIRC. Any strong fuel odor is not normal and a sign that this needs to be done, running problems or not.

HTH