Lift and Tandem Pump Troubles

Mike_04GolfTDI

Mike_04GolfTDI

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Windex said:
This thread is fun.

Now the question is can a gasser in-tank pump supply enough fuel to omit the tandem pump entirely?

Inquiring minds want to know :D
Click to expand...
Sure it could, but you'd need to upgrade your fuel lines, fuel cooler, and fuel filter to handle 100 PSI, and you'd need another pump to make vacuum for the brake booster and VNT control system.

It makes more sense to transfer the fuel with cheap low-pressure components, and then bump up the pressure only at the final point where it needs to be higher pressure (in the passages in the head that the injectors feed from).

I can't think of a better way to run the vacuum pump that right where it is on the end of the camshaft, and since that's gotta be there, you might as well make it pump fuel too.
 
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Inverhyt

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Does the fuel filter act as a regulator?

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Mike_04GolfTDI

Mike_04GolfTDI

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No, the fuel filter does not act as a regulator.

Fuel goes from the fuel tank, through the filter, and then to the tandem pump, where it is essentially blocked until the tandem pump turns, allowing some fuel in, which it then spits out at higher pressure into the passage in the head.

There is a fuel pressure regulator on the tandem pump output, so it doesn't send too much pressure to the injectors. Too much pressure there could end up slipping past the injector seals (O rings around the injectors that seal it into the bores in the head). Fuel that is bled off to regulate the pressure is sent to the fuel return line, which goes back to the filter via the thermostatic T fitting, or back to the tank. When it's cold, the T fitting allows warm fuel to return to the filter to keep it from getting blocked with gelled fuel or ice. When it warms up enough it just returns to the tank.

On the return line to the tank there's a fuel cooler, mounted under the car. This keeps the fuel from getting excessively hot.

Buy yeah, the filter plays no part in regulating the pressure.
 
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Inverhyt

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Cuz if it does the tandem pump shouldn't have gotten anything more than it needs and the pump shouldn't affect much?

I was talking to the diesel tech who put the pump in my car and he had in his notes that the place supplying them used pumps actually gave him a gas one first, which he returned and got that he had to clean diesel out of the pump before installing it into the car, so he was sure it was a diesel pump, but part numbers don't match up?

He said that he would replace it anyways with a part number that matched. He said that the fuel filter should act as a regulator and the tandem pump shouldn't have gotten anymore than it needed.

Because it was a used tandem pump and it could have very well failed just because it was used, unless I can provide unquestionable evidence that the fuel pump is what causes the damage to the tandem pump they aren't going to cover that. They offered a free tow. I declined.

I'm going to put a new tandem pump in and then bring it to the shop to have them put in a new lift pump. The mech was really nice to me and printed out a few manufacturer diagnostic sheets for me so I could do some checks myself.

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Inverhyt

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Mike_04GolfTDI said:
No, the fuel filter does not act as a regulator.

Fuel goes from the fuel tank, through the filter, and then to the tandem pump, where it is essentially blocked until the tandem pump turns, allowing some fuel in, which it then spits out at higher pressure into the passage in the head.

There is a fuel pressure regulator on the tandem pump output, so it doesn't send too much pressure to the injectors. Too much pressure there could end up slipping past the injector seals (O rings around the injectors that seal it into the bores in the head). Fuel that is bled off to regulate the pressure is sent to the fuel return line, which goes back to the filter via the thermostatic T fitting, or back to the tank. When it's cold, the T fitting allows warm fuel to return to the filter to keep it from getting blocked with gelled fuel or ice. When it warms up enough it just returns to the tank.

On the return line to the tank there's a fuel cooler, mounted under the car. This keeps the fuel from getting excessively hot.

Buy yeah, the filter plays no part in regulating the pressure.
Click to expand...
Oh gotcha. Disregard my original statement. He didn't have his computer up so he couldn't check anything, their phones and wifi were down for the day but he asked for me to come by tomorrow for it.

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Mike_04GolfTDI

Mike_04GolfTDI

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He’s probably looking at the thermostatic T fitting and thinking it allows excess pressure to return to the tank.

It doesn’t do that.

It has a check valve and allows flow into the filter, but not out of the filter and back to the tank.
 
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Inverhyt

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I installed a new tandem pump and changed my oil, and just for absolute certainty and photo evidence I got a fuel test kit from harbor freight.

The pump is popping up to 68 psi about when the pump runs and then it's being bled off fairly quickly.

I don't think my tandem pump is bad. I think it might have been the gasket that failed actually. It's completely soaked, the gasket. I'm going to pull the pump apart and see what's going on.

If the gasket failed it would be spraying from all directions right? It wouldn't just tunnel it's way over to the vacuum section for the oil?

I pulled about 3 gallons of diesel/oil out of the car. That seems like a lot for it to just be the tandem pump?

I guess we'll see.

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Mike_04GolfTDI

Mike_04GolfTDI

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Yes, the tandem pump can leak on the inside so fuel goes into your crankcase.

I can think of only a couple other ways that fuel could end up in the crankcase.

One way would be if the O-rings on the injectors leaked, but I believe that is not very likely. The fuel return passage connects between the two larger O-Rings on the injectors, so fuel leaking from the pressurized side would just go into the return passages, which are presumably low pressure. Fuel should take the path of least resistance and just go out the return line. Unless it was installed wrong, it's unlikely that the upper O-Ring would allow fuel to come out into the crankcase.

If you look at a picture of an injector, there are three O-Rings. Fuel supply is between the middle one and the smaller one near the tip. Fuel return is between the middle one and the other large one.

The other way I can imagine fuel getting into the crankcase would be if there's a crack in the head. In that case, fuel could go anywhere. I don't think that's common, and your car would probably run very badly.

It's most likely just the tandem pump leaking fuel at the shaft where it meets the cam. A fuel leak there would go right into the crankcase, because it has nowhere else to go. The gasket between the tandem pump and the head should prevent fuel from going anywhere except into the crankcase. If it's spraying all over, then maybe that gasket has failed too.

Did you replace the electric pump in the tank? That's the one that's putting out too much pressure and possibly making your tandem pump leak. I hope you didn't just put a new tandem pump in and leave the high pressure gasoline engine pump in.

You can pull fuse #28 to disable the in-tank pump. Some cars will run without it, and that would probably be better than sending 68 PSI to your new tandem pump. (Until you can get the proper in-tank pump)
 
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Inverhyt

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Mike_04GolfTDI said:
Yes, the tandem pump can leak on the inside so fuel goes into your crankcase.

I can think of only a couple other ways that fuel could end up in the crankcase.

One way would be if the O-rings on the injectors leaked, but I believe that is not very likely. The fuel return passage connects between the two larger O-Rings on the injectors, so fuel leaking from the pressurized side would just go into the return passages, which are presumably low pressure. Fuel should take the path of least resistance and just go out the return line. Unless it was installed wrong, it's unlikely that the upper O-Ring would allow fuel to come out into the crankcase.

If you look at a picture of an injector, there are three O-Rings. Fuel supply is between the middle one and the smaller one near the tip. Fuel return is between the middle one and the other large one.

The other way I can imagine fuel getting into the crankcase would be if there's a crack in the head. In that case, fuel could go anywhere. I don't think that's common, and your car would probably run very badly.

It's most likely just the tandem pump leaking fuel at the shaft where it meets the cam. A fuel leak there would go right into the crankcase, because it has nowhere else to go. The gasket between the tandem pump and the head should prevent fuel from going anywhere except into the crankcase. If it's spraying all over, then maybe that gasket has failed too.

Did you replace the electric pump in the tank? That's the one that's putting out too much pressure and possibly making your tandem pump leak. I hope you didn't just put a new tandem pump in and leave the high pressure gasoline engine pump in.

You can pull fuse #28 to disable the in-tank pump. Some cars will run without it, and that would probably be better than sending 68 PSI to your new tandem pump. (Until you can get the proper in-tank pump)
Click to expand...
I haven't replaced the lift pump yet but I haven't run the car either. It's sitting waiting for the shop to buy me a new pump.

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BobnOH

BobnOH

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Mike_04GolfTDI said:
..............................Did you replace the electric pump in the tank? ..............
Click to expand...
Geez, lets hope so
Inverhyt said:
...................... It wouldn't just tunnel it's way over to the vacuum section for the oil?
..................................
Click to expand...
Apologies, don't understand vacuum section for oil.
Earlier stated diesel ended up in the sump, that's the oil pan right? Believe most of us are assuming that the overpowering fuel leaked thru the injectors to the upper head and drooled down into the crankcase.
I may be completely out to lunch here.
 
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Inverhyt

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Sorry vacuum section for the brake booster n' stuff I am doing the dumb thing

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Inverhyt

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Would fuel getting into that section affect anything?

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BobnOH

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Well, yea. vacuum system is designed to be dry. You've got several components in that system, some use synthetic (paper like) diaphragms, rubber seals, plastic and who knows what else. Diesel could damage some of that stuff.
 
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Inverhyt

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Would I know if any of it was damaged?

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Inverhyt

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I got a new lift pump in (the right one) and it runs great. The idle seems a little better too I'm not sure. I wonder if my economy will go up. The shop that did the shoddy job is going to give me back the money for the used pump they bought and the one that they would have bought to replace the bad pump. About $200 so it paid for a new pump.

No more fuel in my oil. Changed it with some Liquimoly 5W-40 and the car's great. I'll find a day to pull apart all of my vacuum lines to make sure none of it got hurt.
 
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