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Fuel system?

Tiny
PATRACA90
  • MEMBER
  • 2008 VOLKSWAGEN PASSAT
  • 4 CYL
  • TURBO
  • AUTOMATIC
  • 100,000 MILES
I put $10 worth of gas in my car, however the gas gauge didn't move. The next day it moved up just below a 1/4 of the tank line. The following day it had moved back down to the line when the gas light comes on, ( I hadn't driven but maybe 4 miles on the $10 I had added) so I added $25 worth of gas to drive about 10 miles that night and the next morning another 15 miles. Still the gas gauge had only moved to about 1/4 tank line again. When I left my house again knowing there was plenty of gas I just ignored it because I thought the gauge was stuck. While driving the gauge went to empty and my car stalled like it was out of gas. Towed truck brought my car home an hour later and it started up. Gauge got to empty it cut off again. I have changed the fuel pump with a sending unit on it, fuel control module, and the accessory power relay under the hood. The fuel pump comes one when I try to start it but mow the gauge will not move above empty: I don't know what else it can be.
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Monday, July 17th, 2023 AT 3:55 PM

15 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,269 POSTS
Hi,

You have already done a lot. Since none of those things helped, we need to scan the can-bus to see if there is something stored in any of the modules.

Note: When the fuel pump was replaced, was the fuel level sensor replaced? (See pic below)

As far as the scan is concerned, here is a link that explains how it's done:

https://www.2carpros.com/articles/can-scan-controller-area-network-easy

Let me know.

Take care,

joe
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Monday, July 17th, 2023 AT 8:23 PM
Tiny
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The fuel pump comes with the sending unit on the fuel pump but is that not the same thing?
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Thursday, July 20th, 2023 AT 10:00 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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Hi,

Do you have a picture of what you used? Chances are it is, but anything is possible.

Let me know.

Joe
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Thursday, July 20th, 2023 AT 6:19 PM
Tiny
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It's not the exact one but the one the arrow is pointing to is what I'm speaking about.
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Thursday, July 20th, 2023 AT 6:55 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,269 POSTS
That is the float. It is attached to a rheostat. Is that how yours was set up? The rheostat is nothing more than a resister that changes the voltage signal to the gauge based on the float's position. If that is new and the vehicle stalled when it went to empty, it sounds like there must be a wiring issue. Was the connector to the unit in good condition?

Let me know.

Joe
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Friday, July 21st, 2023 AT 7:07 PM
Tiny
PATRACA90
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Joe, it didn’t steal when it was empty. The car has almost a full tank of gas. I bought a scanner that is shown in the picture but it’s not showing me anything. I mean I’m either not using it right or I need something different but there also isn’t an engine light on either. I am lost at what to do now...I am doing all this myself and I’m not a mechanic lol I can’t take it anywhere because the gas gauge won’t move so it thinks it still has no gas and won’t start and I can’t find a mobile auto mechanic to come check it.
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Saturday, August 5th, 2023 AT 5:30 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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Hi,

I'm not familiar with the scanner you have. As far as the fuel gauge is showing empty, that shouldn't prevent it from starting. Do you hear the fuel pump prime when you first turn on the key?

Joe
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Saturday, August 5th, 2023 AT 11:10 PM
Tiny
PATRACA90
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Yes, the fuel pump comes on. Can you send me a pic or the one your speaking about please?
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Sunday, August 6th, 2023 AT 11:03 AM
Tiny
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Hi,

I would be happy to attach the pic, but I'm not sure what you are referring to.

Let me know.

Joe
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Sunday, August 6th, 2023 AT 9:24 PM
Tiny
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The scanner that you are talking about.
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Monday, August 7th, 2023 AT 8:57 AM
Tiny
JACOBANDNICKOLAS
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Hi,

I attached a pic of one I believe will work for what you need. Please research it before considering purchasing it.

Note: VAG stands for Volkswagen Audi Group. It is specific to their vehicles. Some scan tools may not properly communicate with these vehicles.

Let me know.

Joe

See pic below.
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Tuesday, August 8th, 2023 AT 8:05 PM
Tiny
PATRACA90
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Okay, thank you. I had a mechanic come out and the fuel pump is coming on but when he pushed the valve that’s by the injectors, it doesn’t have any pressure behind it and it’s only like drops of fuel coming out it’s not like spraying out or anything when he pushes it. So, does that mean it’s like something in the lines stopping it up or is it something with the fuel pump? But like I said, the fuel pumps coming on.
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Friday, August 18th, 2023 AT 12:58 PM
Tiny
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  • MECHANIC
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Hi,

You replaced the fuel pump in the tank. Has the high-pressure pump been checked? The electrical fuel pump, located in the fuel tank, supplies fuel to the mechanical high-pressure pump. See pic below.

Was that checked?

Let me know.

Joe

See pic below.
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Friday, August 18th, 2023 AT 9:56 PM
Tiny
PATRACA90
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Yes, I have changed both the fuel pump and the high-pressure fuel pump! Is there a fuel reset button on this car? Or is there a way I can reset the computer or something?
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Saturday, September 2nd, 2023 AT 1:41 PM
Tiny
JACOBANDNICKOLAS
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Hi,

There isn't a reset. I suspect the low-pressure pump isn't working properly. If it was and the high-pressure pump was the issue, you would still be seeing more than a few drops from the test port.

You could disconnect the low-pressure hose at the high-pressure pump and place it in a fuel can to see if the low-pressure pump is providing fuel.

If you look below, I attached the pic of the high-pressure pump and highlighted the low-pressure supply hose.

Let me know.

Joe

See pic below.
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Saturday, September 2nd, 2023 AT 9:08 PM

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