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Discussion Starter · #1 ·
I was doing some research and I have read that in other audi's pre 1991ish they used a coating on the inside of the fuel tank, and that coating after time comes off, and clogs the screen before it leaves the tank, making the fuel pump work harder and starving the motor. I just aquired a '86 4kq, and wonder if i should look into this; i also wonder if my late build 1990 20v 90q has the same issue....
tia...
 

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Re: fuel tank coating (jungle)

I've never heard of this, but that doesnt mean it's not true.
 

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Re: fuel tank coating (jungle)

That's exactly what happened to me, and I'm still in the process of fixing it. If the fuel pump is occasionally a bit noisier (i.e. you can hear it clearly with the car running) or the car cuts out momentarily going 'round sharp corners it's a good sign that this is happening.
Problem is, there's really no good way I can think to fix the problem short of hacking up the fuel tank or buying another one. Let me describe my experience.
Got the car in January and it was doing what I described above. Replaced the fuel pump, accumulator, both filters, and the check valve, and it didn't help.
Figured it must be the fuel tank, especially since fuel would only trickle out when I undid the supply line, as opposed to the return line, where the fuel would fairly gush out when draining the tank.
Pulled the tank. Sure enough, I can barely blow into the supply pipe--there must be an obstruction. Reaming it out with a wire wasn't working. Neither were compressed air or water.
Ordered a POR-15 fuel tank repair kit for about $50. Great product, with excellent instructions. Followed the steps indicated: Rinsed the tank several times with Marine Clean, swished a quart of Metal Ready around in there. Dried the tank out completely. At this point the inside of the tank is spotless and I can blow through the supply line freely. Life is good.
But I had to seal the tank somehow with the thick sealant otherwise I'd have rust problems galore, not to mention a couple of pinhole leaks in the tank. So I poured in the sealant and coated the inside of the tank, letting it cure for a couple of days.
And sure enough, the sealant covered over the screen before the supply exit. I couldn't even blow in the supply line at all anymore. Crap. My options at this point were:
1. Find a junkyard tank with questionable coating integrity and rust issues on the inside.
2. Strip everything off the inside of my tank and try again, figuring out some way to keep the sealant off the screen (I've no idea how I would do this).
3. Take an angle grinder/dremel to the bottom of the tank, clean/remove the screen manually as best I can, and MIG weld everything back up.
I'm currently in the middle of option no.3. I plan to take pictures tonight so you can see how the inside of the tank (at least underneath the baffle) is put together.
Hope that provides some insight.
Best,
 

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Discussion Starter · #4 ·
Re: fuel tank coating (spaceship)

how hard is it to remove the screen? i have heard some people just take the screen out and replace thier fuel filter more often. So with out that coating the tanks will rust, and that rust will clog either the screen or filter or fuel pump or injectors.....GREAT!!! hmmmm maybe i should get a fuel cell.
 

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Re: fuel tank coating (jungle)

The screen requires cutting the tank open to remove.
Without the factory coating you just coat the inside of the tank with fuel tank sealer, as I'm doing. It's a thick, gummy coating that prevents rust and seals small pinhole leaks in the tank.
The screen would only filter out the largest particles. Between two easily-accessible and relatively inexpensive fuel filters, I think I'll be alright with the fuel tank sealer and no screen. I guess we'll see.
 
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