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Misfire, no acceleration, rough idle

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A8 / S8 (D2 Platform) Discussion Discussion forum for the D2 Audi A8 and S8 produced from 1994-2002

Misfire, no acceleration, rough idle

Old 10-01-2018, 03:49 AM
  #51  
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Join Date: Oct 2005
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I've added fuel via the filler to a nearly dry tank to reprime the system and it took a few fills (fill, start, run, stumbles, dies) of maybe a half gallon each before it cleared all the air out of the scavenge system and ran properly. I think this is a good way to do it so you know the system is working properly before refilling the tank to the point where it runs without the scavenge system.

I think it works better to add small amounts as you may need to refill the fuel cup several times to get all the air out of the system and that happens via a small amount of the gas you put in getting diverted to the fuel cup. If you just put in 3 gallons that fills the cup once, maybe not enough to blow out all that air in the scavenge system, and also not enough to drown the fuel cup. Better IMO to add a half gallon three times or however many times is needed. You can even add more while it's running if you hear it start to stumble.
jfrahm is offline  
Old 10-01-2018, 09:54 PM
  #52  
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Join Date: Jan 2004
Posts: 585
Default A pint

I've done a few. The fuel filler pipe should pour right into the cup. I've pumped out on a new install until the tank was empty and sputtering, poured in a gallon and then pumped a little over 3/4 of it back out.
I suppose at such a low level the angle of the car on the ground might matter. Mine were parked level or nose low. Regardless, it takes very little to prime the pump. Install it, pump it all out using a threaded fuel barb, then add a gallon or two tops and you should get nearly all of it back.

I had to cut my first one out with a foot long hole saw down over the retaining bolt and took EVERYTHING out. If it doesn't prime on less than a gallon from empty, then your fuel filler pipe (unclipped?) is not aimed into the cup assembly, or you have a leak on either one of the far reaching suction hoses or the high pressure hoses from the top of the pump. The in the tank suctrion/venturi hoses can become unclipped from the bottom of the cup assembly if you yank it about. The ends are easy to reshape to clip on more securely.

if you are not pissing into the cup when you refuel, but always fill the tank completely, then you will never notice if your aim is off, because the cup , once primed, will stay primed unless you run it completely empty. However, if you run it empty, and only add a gallon or two, it will pump out completely if everything is right.
BrianC72gt is offline  
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