A very interesting thing happened today.

SilberUrS6 · 03-09-2012, 07:31 PM

First thing that happened - fuel gauge was reading half full, at 330 miles. Now, wow - I can drive it that hard and get over 25mpg? NICE!

Look down in the next minute and the warning lamp is lit. Hmmm. Pull into the garage and notice the idle is a bit lumpy, and remember that the hesitation at 1800RPM has been a little worse today. Kind of a stumble more than a hesitation. Think about that a bit as I let the dog out and see if the guinea pig has given birth yet. (Grumble - I'm not a fan of rodents in the house already. But that kid just *HAD* to have the damn thing... It came pre-impregnated, too.)

Go back out and get in the car to take it for a drive to pay attention closely to what it's doing. Idle is definitely worse, and the car is not accelerating as well as it did before. Fuel gauge is reading half-full again. :S

Well, let's just see what the real deal is with the fuel - go and fill up with Chevron 92. (That's [R+M]/2 to those folks across the Pond - 98 in your neck of the woods.) and fire up the car.

Smooth idle is back. Get going - very minor hesitation at 1800, and I have to pay attention to notice it - if I hadn't been looking for it, I wouldn't have noticed. Car is now *fast* again. Like it just got over some automotive flu.

Now, I remember back to when I filled the tank last - it was in late December. So, this fuel is 3 months old, *and* the bottom of the tank. So, old fuel, or weak fuel pump, or both?

porwolf · 03-09-2012, 07:36 PM

What about the fuel level sending unit? They can be delicate and are subject to corrosion. Could it have been that the 1/2 full reading was off and there was hardly any gas left in the tank before you filled it up again?

Oh Haha · 03-09-2012, 07:37 PM

By "warning lamp", do you mean the low fuel light or the alternator lamp due to the low idle speed?

If the fuel guage is working fine I would add some fuel stabilizer to the tank. Gas that's just 3 months old shouldn't cause any major problems.

pegasus9 · pegasus9's Garage

When my engine had hesitation symptoms it turned out to be the fuel pump.
Maybe change the fuel filter and go from there.

I'd add some fuel stabilizer i.e. stabil next time you think you're gonna shack it up for 3 months.

And my fuel gauge was pegged half away all the time even when I topped it off, typical of a bad sender.

SilberUrS6 · 03-09-2012, 07:44 PM

To clear up - the gauge light was the low fuel warning lamp.

The car took 18.9 gallons. So it was close to being done.

We'll have to see on the next tank about the sender and the pump. I guess I get to do some reading on changing the fuel pump and filter (and possibly the fuel level sensor.)

porwolf · 03-09-2012, 08:11 PM

Actually, if you are in for it, you can repair the fuel level sender unit. I have done it recently. There are some good threads on this forum. Also, if you suspect dirt in the fuel coming from the tank you should take out the mesh filter from the tank bottom, if your tank has one of those. You can replace them for about $50.- if needed. That would be your first line of defense against dirt coming into your fuel system.

SilberUrS6 · 03-10-2012, 07:03 AM

I think I will do the stuff in order - run this tank to see what happens when I get down to <2 gallons. If I get the same symptoms on fresher gas, then I have a pressure problem. At that point (without adding more fuel), I will change the filter, and run it again. Same symptoms indicate fuel delivery pressure issues, which *probably* indicates a fuel pump.

I am SO glad the pump on these cars is not in the tank. My S6 has an in-tank pump, and what a total PITA to have to be completely in the trunk with one arm down the hole trying to release clips that *really* need two hands to do well...

External pump with nice banjo fittings. Eric says, "WIN!"

DRACO A5OG · DRACO A5OG's Garage

I had the same issue, read half full but the low fuel light came on.

I removed the gauge and re-flowed the solder joints and issue fixed.

December? damn that is a long time. Since adding new clean fuel, it probably reduced any moisture that may have built up but it appears your filter may be clogged, replace it or remove and clean it out and replace or add some BG44K into it, it will definitely clean out any soluable debris.

Follow BG44K instructions to the letter do not add too much it will each any weak rubber/plastic fuel line components.

Jim

brads911sc · brads911sc's Garage

Mine runs like that when i almost run out of fuel.. I try to keep her above the warning light level since i assume that 30 yr old fuel guages may not be perfect... and i dont want to be left sitting somewhere due to running out of fuel...