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VW MKIII-A3/B4 TDIs This is a discussion about MKIII-A3/MkIII Jetta/Golf (<99.5) and B4 Passats (96,97) TDI's. Non TDI related postings will be moved or removed.

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Old November 13th, 2017, 16:09   #1
argiopeweb
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TDI(s): 1997 Passat
Default Fuel filter drains on incline

Recently acquired a 1997 B4. On two occasions, while parked on inclines and left for ~24 hours, the car will start, run, and stumble to a stop in <15s with an empty fuel filter.

There is no smell of raw diesel in the engine bay and no sign of leaks around the IP or under the (new) fuel filter. No puddle of diesel on the concrete.

Is there a check valve somewhere toward the fuel tank that may have become clogged? Any suggestions are appreciated.
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Old November 13th, 2017, 17:42   #2
Mongler98
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no check valve. the IP (injection pump) sucks fuel from the tank though the fuel line from the fuel filter. 99% of all TDI's this make have air bubbles that come from the o'ring failure issue on the return line from the ip output back to the tank. my guess if yours is bad enough that its letting the line have a suction leak. your not going to see fuel leak or smell because its like sucking from a straw, not pressurized. Check the lines for leaks, cracks, etc. a leak will let air in and siphon the filter dry. my guess is at the filter or from filter to IP. You can get a uber kit from nicktane. You can also do the Dietzl mod, same things, just cheaper and a tiny bit more work involved. this eliminates the bubbles in the line and solves the o'ring issue. normal to see air bubbles in the line but if its bad enough it will drain your filter.

http://nicktane.com/

http://forums.tdiclub.com/showthread.php?t=352652
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Old November 13th, 2017, 18:55   #3
ToddA1
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Check valves will be at the sender.

-Todd
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Old November 13th, 2017, 20:07   #4
Abacus
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Todd is correct, there are 2 one-way valves (check valves) at the fuel sender on top of the fuel tank. It is (was) a common practice to drill them out during cold weather since it's the first place the fuel will gel because it's a restriction. I do not believe in the practice and instead just prevent fuel from gelling with an additive.



There is also a check valve on the injection pump itself, where the return line exits the pump. I've had that one go bad before and prevent fuel from flowing forward.


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Last edited by Abacus; November 13th, 2017 at 20:14.
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Old November 14th, 2017, 11:08   #5
argiopeweb
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Thanks for the quick replies, all. I cut the pinch clamps (they'll be replaced with fuel injector clamps) and pulled the supply and return check valves out of the car. Return line was empty (expected) and check valve checks out with good flow. Supply line was also empty (expected if the supply line was siphoning) and the check valve has lower flow both directions than the return check valve in the correct direction.

Supply check valve is now in the heated solvent bath being ultrasonic cleaned. With any luck it will come free. Otherwise, I'll need to source a new part.

Any chance this is a confounding issue rather than the primary problem?
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Old November 14th, 2017, 13:51   #6
jdulle
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the recent fuel filter I had my mechanic install (Mann brand), while he was resealing the IP, had a leak in the top of the cartridge allowing air into the system. He said it took him a while to find it and when he did he siliconed around the top of the cartridge and its been fine ever since.
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Old November 14th, 2017, 15:46   #7
argiopeweb
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Pulled the check valve out of the bath and ran some water through it with a (needle-less) hypodermic syringe. Big ugly chunks of brown gook came out. It's now water tight in the reverse direction and has good flow in the forward direction.

I'll note that blowing through the check valve in the forward direction still barely lets air through (presumably due to the high spring pressure of the check valve and the low PSI capability of my mouth), unlike the return valve which requires very low pressure to flow freely in the forward direction. The moderate pressure of a 20cc syringe ("sealed" by pressing them together firmly) is strong emough to induce good flow, so I'm going to assume the IP lift pump is entirely sufficient to overcome the spring pressure.

Quote:
Originally Posted by jdulle View Post
recent fuel filter had a leak in the top of the cartridge allowing air into the system
Well, that's remarkable. I'll have to keep an eye out for that. I had considered the water drain, but not a manufacturing defect like that.
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Old November 14th, 2017, 20:48   #8
Abacus
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Quote:
Originally Posted by argiopeweb View Post
...I'm going to assume the IP lift pump is entirely sufficient to overcome the spring pressure.
There is no factory lift pump in these cars, but it's somewhat common to install
one off a BEW. Was that done or is yours stock? If stock, it's suction all the way from the sending unit to the pump.

It's also not unheard of to get the wrong filter. The 1Z/AHU uses a different filter from the ALH. While they look similar they are not interchangeable. I wonder if this is the cause of the leak jdulle described. I've also seen cracked thermostatic-T's, which can introduce air and cause a bleed down.
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'96 B4V: 357,000 miles Malone 2+, PP520's, 6 speed, 02J short shifter, E-Codes, G60 brakes, Evo plate, DMF, stainless exhaust, heated leathers, cold weather package
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Old November 14th, 2017, 22:33   #9
Steve Addy
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Quote:
Originally Posted by Abacus View Post
There is no factory lift pump in these cars, but it's somewhat common to install
one off a BEW. Was that done or is yours stock? If stock, it's suction all the way from the sending unit to the pump.

It's also not unheard of to get the wrong filter. The 1Z/AHU uses a different filter from the ALH. While they look similar they are not interchangeable. I wonder if this is the cause of the leak jdulle described. I've also seen cracked thermostatic-T's, which can introduce air and cause a bleed down.
The thermo T system is a great idea but as someone else commented in another thread they often don't work the way they should.

This is one reason I've gone to the Mk2 fuel filters that don't use the thermo T, it's less complicated and there's no chance that air will be introduced via the thermo T.

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Old November 14th, 2017, 22:46   #10
argiopeweb
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Quote:
Originally Posted by Abacus View Post
There is no factory lift pump in these cars, If stock, it's suction all the way from the sending unit to the pump.
I was under the impression there was a low pressure mechanical suction pump included in the VE pump package that fed the high pressure injection pump. Happy to be corrected if that's incorrect.

No electrical pump upstream on my car that I saw, though I didn't take out the (pretty stock looking) sending unit.

Quote:
Originally Posted by Abacus View Post
I've also seen cracked thermostatic-T's, which can introduce air and cause a bleed down.
Yet another thing to be on the watch for. My thermo T made some pretty ugly noises when it came loose of the old filter. Thanks!
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Old November 14th, 2017, 22:55   #11
Steve Addy
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Quote:
Originally Posted by argiopeweb View Post
I was under the impression there was a low pressure mechanical suction pump included in the VE pump package that fed the high pressure injection pump. Happy to be corrected if that's incorrect.

No electrical pump upstream on my car that I saw, though I didn't take out the (pretty stock looking) sending unit.
There is no electric pump in the system. The IP has integral mechanical lift pump that pulls fuel directly from the tank. The system is identical to what VW has used for years.

As Mark mentioned some have fitted electric lift pump from the BEW cars but it's really not necessary.

Quote:
Originally Posted by argiopeweb View Post
Yet another thing to be on the watch for. My thermo T made some pretty ugly noises when it came loose of the old filter. Thanks!
Over time the T fittings get brittle and can break. Also, the o-ring on the fuel filter can degrade over time too. If the filter is old stock it can have a defective o-ring and that will cause air leaks. I pulled one out of my stock a while back and the o-ring wasn't worth crap. That's one reason I've got a few o-rings for those.

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Old November 16th, 2017, 14:05   #12
peteguenther
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My 2003 wagon has what appears to be a check valve in the supply line right above the tank. I suspect it of failure as fuel flows right back after I suck it through the filter. Anyone else know of this?
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Old November 16th, 2017, 16:04   #13
Steve Addy
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Quote:
Originally Posted by peteguenther View Post
My 2003 wagon has what appears to be a check valve in the supply line right above the tank. I suspect it of failure as fuel flows right back after I suck it through the filter. Anyone else know of this?
It's a reasonable assumption based on what you observe, fuel should not flow back to the tank via the supply line is the one-way valve is working correctly.

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