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Fuels & Lubricants Discussion all about Fuels & Lubricants. synthetic oil, conventional oil, brands, change intervals, diesel grades, gelling and such debated items like that. Non TDI related postings will be moved or removed. This forum is NOT for the discussion of biodiesel and other alternative fuels.

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Old June 17th, 2017, 20:47   #1
tdi-wagoneer
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Join Date: Dec 2006
Location: Anton Chico, NM
Default misfuel, driven & died, fuel draining, liftpump failure

I have a misfuel situation that has I believe been poorly handled.

Here are the points:

1 - My wife fills up our 2005 tdi which we have had since it was new. Vehicle had 1/8 tank when fill up occured. She is not sure she put diesel in the tank and the car seemed to run badly.
2 - Drove car approximately 100 miles until it died.
3 - Delivered car to local mechanic with instructions that a misfuel occurred and to to drain tank and flush the system.
4 - Mechanic drains tank by using lift pump, replaces filter and adds diesel.
5 - I get car back and diagnose a failed lift pump. Fuel from pump before filter is green but fuel return before pump is black.

Here are my questions:
1 - With a ratio of 7:1 gas to diesel can you drive 100 miles?
2 - Using lift pump do drain contaminated fuel from the tank seems like a bad idea as it could trash the pump and you might not get all of the fuel out of the tank?
3 - I know the pump died but I do not know if it died after pumping all the fuel it could out of the tank.

Let me know what you think.
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Old June 18th, 2017, 10:04   #2
QuickTD
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A PD is pretty forgiving of low lubricity, but 100miles is a lot. If the weather was warm it would probably stay running, but poorly. I doubt it would restart if shut off. Hard to say if it hurt anything. Does it run OK now?

It's possible that pumping out that much gas could have killed the lift pump, but they also die from natural causes. Often it isn't discovered until you change a filter and need to prime the car again. A marginal pump may still pump into an open hose, but not make much pressure. I probably would have siphoned the bad fuel out since access to the sending unit is easy and it would probably be faster.

PD return fuel is often a bit black due to engine oil contamination. The injector plunger has no seals other than a close mechanical fit so a small amount of engine oil tends to get in there. Usually just blackens everything in the tank.
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Old June 18th, 2017, 16:18   #3
tdi-wagoneer
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Location: Anton Chico, NM
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Thanks QuickTD,
Car runs well except for being starved for fuel by lift pump. I can get 4k rpm for an instant on the road until fuel is used. 2500 rpm is doable.

Lift pump was less than 1 year old and its symptoms of the prior failure were subtle. Misfire going uphill and at 75mph. The behavior is much worse (see above) with merely a spurt of fuel (1/2 cup or so) before no flow for an open hose.

A concern I have is that the lift pump failed before pumping out the contaminated fuel and that the lift pump did not remove all of it. I think I should consider the tank contaminated and drain it.
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Old June 19th, 2017, 01:39   #4
Mako
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The in tank lift pump is no different to the lift pump in petrol tanks. The lift pump will fail if it's allowed to run dry such as when it's hotwired and left to pump while the mechanic has a tea break. Black fuel is normally associated with leakage on the seals that isolate the delivery and return fuel galleries in the cylinder head. The copper seal at the base of the PD unit can allow combustion gasses to enter the fuel galleries if they are faulty. It's not uncommon but needs to be fixed. Did the shop remove and replace the PD units by any chance?

Last edited by Mako; June 19th, 2017 at 01:42. Reason: spellink
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Old June 19th, 2017, 05:26   #5
tdi-wagoneer
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No PD seals replaced, tdi has about 200k miles on the engine. Mechanic claimed it wasn't left unattended.

Got a pump on order and I'll replace it myself.
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Old June 19th, 2017, 07:31   #6
Mako
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PD's can run well without the lift pump if the supply line has no restrictions. I've run my PD for many years without a lift pump. The only drawbacks are difficulty scavenging the last fuel in the tank when climbing a hill and slightly more difficult to prime when changing fuel filters.
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Old June 21st, 2017, 19:27   #7
tdi-wagoneer
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Default new pump, odd behavior

So I installed a new lift pump and it behaves like the old one and the vehicle runs perhaps a little better.

Installed a new fuel filter after the test drive with new lift pump, filled the new filter using the VCDS to run lift pump for approximately 30 seconds and fuel is being exited from the pump.

Now the car will not run at all?

No faults displayed via the VCDS.

Now I'm wondering if air in the lines, injection pump failure, or shutoff valve has stopped at injection pump?

The mechanic who drained my tank told me he used the lift pump. How could he do that considering the lift pump as I observed only puts out about 1/2 cup of fuel when the ignition is cycled? Is there a jumpering of some circuit?

This is getting bad.
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Old June 29th, 2017, 17:18   #8
Dannyboy
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You need to run the pump more than 30 seconds, PDs are a bit of a pain to bleed but it will fire eventually
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Old July 3rd, 2017, 14:41   #9
tdi-wagoneer
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Default Up and running, Tandem pump at fault

As DanyBoy suggested, I ran the lift pump quite a while using my VCDS and it took some time to fire up.

Still having the low power and appearing to be starved for fuel at rpms over 3k I put in a new tandem pump on the suspicion that at 200k miles and 90 miles being run on gasoline compromised it. I should have done the pressure test on the pump to be thorough but guessed right and the tdi now runs much better than it has in a long time I think the injectors may have been cleaned by the gasoline and that the original pump was worn.

Made a couple of mistakes installing the pump such as folding the alignment tab for its gasket under and spilling fuel and also crossing fuel lines by following the flow arrows on them which had been connected opposite by someone else previously.

Primed the tandem pump using my Mityvac before starting and after some cranks started up.

One change to the system here was installing clear fuel lines from filter to engine. This I appreciate as I now can see fuel out and returning checking for bubbles and discoloration. The black fuel I saw before is no longer present and there are no bubbles either.

A thought I had was to have a permanent pressure gauge on the tandem pump test port. May just do that.
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