2000 Volkswagen Beetle Fuel Pump knocks loudly

Not sure that I can help, but certainly willing to try.

You are positive this is coming from the fuel tank area?

Does the noise ever get louder?

Does it ever increase or decrease in repetition?

When you first turn the key to the on position, before you crank it, does the noise happen as the pump is being energized?

I know some GM have a pulse dampner, not sure on the beetle.

If you have the old one, can you hot wire it to observe any anomolies?
I need to read through my tech software to see if I can pry out something to work with.

I did find a tsb that my be unrelated, but want to share it regardless because I would gather low oil pressure may continue this condition:

Engine - Rattling Noise On Start Up (Normal Condition)


Condition
Camshaft Chain Tensioner(s) or Camshaft Adjuster(s), Rattle or Knocking Noise


Technical Background
The camshaft adjustment is hydraulically actuated and controlled by the engine oil pressure.

If the vehicle has been sitting, with the engine turned off for a period of time, the oil accumulation inside the camshaft adjusters partially bleeds off and the oil flows back into the oil sump.

To ensure an efficient camshaft adjustment after an engine cold start, the oil pressure inside the camshaft adjusters must be built up as quickly as possible.

During this time a slight rattle or knocking noise may be audible.

This noise is normal at engine start and will last until the oil pressure is fully reinstated.

I found another one regard the trunk lid. I want you to open the trunk lid and keep it propped while you see if the noise is still present.




PAul

The fuel pump is stand alone under the back seat. You can remove it from the inside. When I start it for about 30 seconds or so it runs great and very smooth. After that the knock starts out soft and builds real fast to a loud pound. I can feel it also when I put my hand on it. Especially on the fuel return side of the pump. The engine then starts to idle rougher. The sound stays the same after that and I can hear the pump behind the knocking going up and down slowly in pitch..like a wave. My old one made the same loud knocking sound right before I pulled it into the garage to change the pump out. Weird. Nobody can tell me what it is. Some say bad fuel, others a pressure pump.

A defective pump is possible, seriously doubt a bad gas scenario.

I am thinking a restriction a line maybe in the return line. Check and monitor the fuel pressure from start up.
I would do this not only to determine the symptom source, but the reason for the runniblility issue. I would not be surprised if you find the pressure goes out of spec. as it warms up. If I am right, I would pull off the return line at each end and blow compressed air through it, replace the filter and do the same on that line as well as the vent line.


Also on the fuel filter replacement, I would question it. Any time I do a fuel pump, we do the filter. I don't care if it was done the week before. I have seen filters start to plug up very quickly in some cases.

Thanks. I will replace the filter and take the return line off. How do you check the pressure?

Do you have a fuel pressure gauge?

OEM style:
VAG1318 pressure gauge
Adapter 1318/9
Adapter 1318/17

Aftermarket gauges should work, but you'll need the right adapters.

IF yes, I'll send the procedure.

I don't have tools like you guys do..I'm just a weekend warrior..now over my head. I can't even move it to a shop.

Maybe I missed it, but I thought it runs, just rough.

Can you get the lines disconnected and blow air through them?
Even if you buy a small compressor, it is something that always comes in handy around the house.

IF there is a restriction, this may be why the pump goes from good to bad.

Another thing I might try is to disconnect the return line and run it into a container and visually see if the volume starts dropping off as it gets worse.

It runs rough at idle and when I talk my foot off the gas (all this is in my driveway) it seems like it wants to stall..but doesn't. I'm just afraid it will stall on the road and it is about 15 miles to the nearest shop that works on VW's. This after noon I am going to try all you recommended this morning. Disconnecting the return line should show a steady stream of gas into a container when started right? and is ok to run disconnected? I will pay more if any of this works.

The return line is just returning the fuel that isn't used, so it isn't a problem doing so with any I have worked on.

Hey,
I was talking to the top Monkey around here on your car. DId you replace the pump with a after market pump?, If so What brand? Or did you get one from the dealer? With the exception of Delphi, All the other aftermarket ones really have bad track records.

It is a Delphi OEM pump.

Good.
You may want to give delphi tech support a call at 1-877-go delphi.

I will do that...thanks

I was going to call Delphi but there are to many numbers. 877/go delphi

LMAO!!!

I had sat there for about 5 minutes writing it out and kept getting 8 numbers too. I got it from both my supplier and the Delphi website. Finally I just copied and pasted it from the site. I was hoping it worked, but didn't ty it.
... I'm gonna dial it and see what happens.

Sorry..Didn't mean to laugh...

HEH HEH...and you doubted me! HAHA!

When you call the number, keep in mind the menu has changed on December X, 2008.

On the serious side I hope they can give some more technical logic that brings this to a close.

Did you try blowing out the lines?

Oh man..I had to laugh also about being so dumb! Of course, the telephone only dials 7 numbers...duh! I called but they were busy. I am going to recall this morning. I haven't blown the lines out yet..tomorrow I am spending the day on the 'dub. You have given some good ideas. Hopefully they will end this nightmare for me! Question, I know where the return line terminates into the pump. Where is the other end? Thanks

look at the fuel rail 9 is the pump 16 is the pressure line 13 is the rail

Great schematic. That helps alot. I just talked to Delphi and they are kicking in the wind like we are. I am going to check the lines tomorrow as you suggested. It has a black and blue fuel line on top of the pump, what color is output and what color is input? Dephi wanted me to check that it was installed correctly and not touching the bottom. I lined the pump up to the hole facing the trunk which is where I think I remember it was. I have the blue line hooked up to the return side..right?

I would think the blue is return and the black pressure, but I don't know that is true. I doubt it would have started if they were reverse.

That's what the Dephi guy asked if I had switched the lines on installation. I told him the same thing that I don't see how it could run at all if I did. He just kept saying "anything is possible" that's not the asnswer I seek *S*

Welcome to the world of professional auto repair...LOL...

There are times you shake your head because you just can't believe how Chaotic it can get. More often than not it comes down to your raw ability to troubleshoot. Even then you can get to a point of..."I sure hope this is it"! LOl...

Will the parts store be willing to swap it out?

Seems to me that the symptom of making noise that continues to get worse parallels the pressure that would rise as the pump pumps but a partial restriction causes a slow increase in pressure until it reachs peak backpressure and a transfer of energy is causing a shaking that is causing the noise. Where the vibration is may be irrelevent but since it seems to be on the return side, I would make that the priority, but it can be anywhere in there.

Ok...I took out and reinstalled the pump for the 3rd time now. I blew out the return line and the gas came out clear. BUT..a change..it ran perfect for about 10 mins before I heard the rythmatic knocking come back and the engine then began to run rougher. The return line blew through without any prob. I felt the lines as it was knocking and the output line was still smooth and I felt all the vibration in the return line. I have a new filter ordered and will change that out when it gets here. I was so stoked because I thought we fixed it after it ran 10 mins. I am going to look at your schematic and see where else it may be. Now what?

Ugggghhh....
Well at least the symptoms changed....
Why would the runibility change?
Going into open loop?
A second problem?

I sure wish I knew what was happening whith the fuel pressure when it runs poorly.

Gotta give this thought.

Man! the schematic you sent covering the fuel system shows the system to be friggin simple. There's not much to breakdown. Tomorrow my fuel pump should arrive. I would think the pump is defective if not for the fact my old pump started making the SAME sound before I pulled it into the garage to fix. I changed the filter about a month ago but am going to change it out. There's nothing left I can see to breakdown and cause the noise.

LOL...I mis-read, I thought you did replace it again...whew...I might want this to be the fix more than you lol.

Yeah it is basic, but why on the return side is the vibration present?
Power is good to pump? Can you see me bracing for the chance the pump that is in there is good?

Picture being in front of a customer and telling them that chances are good that the pump is the problem, but you just can't gaurentee it.

Ahhhhh!!!!! I am just so frustrated with this car. AND I'm sorry I'm getting my pumps and filters mixed up. I DID change out my old PUMP. The new one is installed and making the noise. I thought it was the pump because my old one started making the noise about 10 mins before I pulled it in the garage to change it out. I was trying to go up a hill to get home and the more gas I gave it..the slower and more stumbling it became. This new pump is making exactly the same noise. The FILTER I just ordered thinking...WHAT ELSE CAN BE WRONG! *S* and it arrives today. As far as I see in your diagram..there is nothing left..but obviously there HAS to be.... (now banging my head on my desk)

Anything different with the new filter?
did you try to tap out the filter to see if any debris was in it?

I don't know that it is possible, but the filter you replaced the first time wasn't installed with the flow going in the wrong direction was it?


When you checked the return line, did you disconnect both ends to blow it out. Presence of fuel does not mean there isn't a restriction. A restriction can be partial.

It is solved! I changed the fuel filter yesterday and I drove it to work today. No knocking! How do I send you a tip? You deserve it for sticking this thing out with me.

I'm really happy for you!!!!

REALLY!!! LOL!

Wasn't sure where to go next.....damn VWs ;-)
I wonder if the old pump was really bad... :-0

If you want to leave some feedback, that would be appreciated.

Enjoy the week end.