Jetta Fuel Sending Unit/Rear Seat Removal

Hello,

After several years of my Jetta being garaged, I finally put it on the road again and of course there were some problems that appeared, which weren't there before. The main one's I've worked on, but I was hoping someone might help me with this one.

My fuel gauge, even though the tank is full, is registering just above the "low" red zone and never goes higher than that. I wanted to get to the fuel sending unit, which is under the rear seat to check it out, but I can't quite figure out how the rear seat comes off. I found the 4 nuts near the arm rest on the rear back cushion seat and do see those four black clamp type hooks from the inside of the trunk, but I know there has to be something else.

Can I simply remove the lower seat, without removing the mounting hardware for the rear back part of the seat? How? I don't want to force something and later find out that it snapped, if you know what I mean. The Chilton books, simply talk about it in general, but no specifics. If you can help me I would greatly appreciate it.

Thanks,

Roger

Well, if it's anythink like my Corrado: Yes you can.
The a2 seats can be hard to get out, but it shouldn't be too hard.
You need to push the cushion towards the back of the car, and then lift it up in the front. Mine came out just by giving it a good punch. some people sit on it and push backwith their legs, and the pull up.
Anyway, push back and lift up.

Hi,

Well that does not seem to work, our seats might be attached slightly differently. You can sit in the rear seat and try to push back with your legs, but the seat does not move back, since it is already hitting the rear wall in the trunk. There are these three black tabs at the bottom front of the seat cushion, but I'm not sure how to manuver them.

The seat appears solidly atached, even though I have released the two hooks from the seat back from inside the trunk. There still is something hold it in place.

Other thoughts?

Roger

Well removing the rear seat would be the wrong thing to do. The fuel level sender is accessable through the trunk. First pull the trunk liner out, then remove the 3 screws that are on the black cover on the passanger side of the trunk floor. The fist thing I would do at this point would be to check the gauge itself. There are 4 wires in the plug there. The 2 SMALLER wires are for the fuel gauge, the other 2 BIG wires are for the fuel transfer pump. Take a wire and jump the two SMALL wires together while the key is on. If the fuel gauge moves to way past full, then you should be good. If not, you got problems. Check the ground wire, (the brown wire) for resistance to the body. You can either do a voltage drop test or an ohms test. If you still think that you need to pull the fuel level sensor out, remove the two fuel lines. Don't forget to replace the hose clamps when you are done. Use a big screw driver and a hammer and force the black lock ring counter clock wise and it will come out. There you will see the fuel level sender and the Transfer pump. Now the transfer pumps are know to go bad quite offen, So now would be the time to change it. Put everything back together and hope that it works. Oh, be carefull with the black gasket that goes onto the top of the tank. I find it easier if the seal get placed onto the tank first and then the sending unit get put in. Look for the Arrows (one on the tank and one on the sender) and line them up when putting the sender in and the lock ring on.

Good luck

Todd

Hi Todd,

Thanks for the detailed explanation and also for the correct location of the fuel sender sensor. I won't worry about the rear seat, ha! ha! However, you mentioned about a "Transfer Pump". I know it can't be the Fuel Pump, because that is under the car, outside under the rear right passenger side. What is the Transfer pump - it's purpose? Is it part of the fuel sensor assembly?

Wanted to get an idea before I remove the black ring to get to the sensor. In the interim, I'll check the wiring as you mentioned. As a reminder, my car is an '87 Jetta.

Thanks,

Roger

Hi Todd,

The fuel gauge worked, when I jumped the two small wires, so I would be inclined to think that it is the fuel sending unit. However, what does the Transfer Pump do?

Because the other problem I am experiencing is that when the tank is about 1/2 full (I say that because all I was able to put in was about 7 gallons and it's a 14 gallon tank), the car begins to die at idle and I can hear the fuel pump's sound change. If I try to give it gas, it hesitates and chokes off. This problem has happened twice already and I was lucky to just make it to the gas station and filled it up. Then the problem went away after fill-up (different gas stations). Also both times happened around 150 mile odometer reading. I was begining to think that it might be the fuel pressure regulator, but now I wonder, since maybe something with the fuel sensor/transfer pump is causing a problem.

Any ideas?

Roger

The transfer pump is there to move fuel out of the tank and into the "black box" the main fuel pump is in. On the old VW's, A1 chassie, the fuel pump was connected to the bottom of the fuel tank, and gravity feed fuel to the pump. Because of the addition of EVAP fuel vapor systems to the 85 and up cars VW had to rework the fuel system. So they moved the fuel pump ahead of the axle. Since they could not longer draw from the bottom of the tank, they put a pump into the tank to feed the main pump.

The problem about dying when the tank is about 1/4 full is just about right for a bad transfer pump. When the pump dies the main fuel pump has to the sifen the fuel. This will cause fuel starvation when at wide open throttle (WOT). It will also cause fuel starvation when the tank is low. Also when you are in there, check the fuel lines that run to the sender. The blue line is the return line, and need to go onto the nipple that has the arrow pointing into the sender. The black line is the one that goes to the main pump, so it goes onto the nipple that has the arrow going out.

There are two way to quickly check the transfer pump. One is to start the car up and listen at the fuel tank for a hummmmmm. The second way is to pull the black hose off, remove the electrical connector and start the car. a quick tap of the electrical connector onto the plug and fuel should come out of the nipple with the arrow going out. If not then the pump is bad, or the wires going to the pump are bad.

I have found on some A2 cars that there is a high voltage drop in the ground wire to the main and transfer pump. I take a piece of wire and tap into the big brown wire and then screw it down as a helper ground.

Good luck,

Todd

Hi Todd,

Well, now things are beginning to make more sense and I can see how the Transfer Pump can contribute to my problem of stalling out. No doubt I can hear the main pump changing pitch or sounding louder as the tank is past the half way mark. Tonight it started fine as always on the first crank (it's still cold here in New York), but after 20 minutes of running it began to stall out and you could hear the main pump's sound pitch change. Almost the same syptoms as vapor lock one experiences in the summer months, especially caused by a clogged fuel filter.

I checked the transfer pump as you indicated. I pulled out the electrical connector at the fuel sensor and cleaned the contacts, then applied a coating of die-electric grease to insure proper connection and prevent future corrosion.

I could hear the Transfer Pump humming when the ignition is on. However I guess the only true way to know is to disconnect the outlet line and make and break the electrical connection for the Transfer Pump to actually see fuel come out. I know I am going to have to more than likely replace the fuel sensor, but is there anything else I can/should do with regard to the Transfer Pump, since it does sound like it is working based on it's humming sound?

Can the fuel filter after the main fuel pump be causing this type of problem because the pressure in the system gets too high? I also notice a relay next to the fuel mixture control unit that clicks quite often and the RPM's fluctuate slightly almost constantly.

As an aside, on the black cover, VW wrote in yellow ink, 1/17/95 (of course the car is an 87), so the dealer must have done something, maybe a recall back in 1995 in the fuel sensor/transfer pump area. I notice that the electrical 3 wire plug coming from the fuel sensor unit gets split into a two wire connector and then the wires diappear through their harnesses. Almost looks like a modification done after manufacturing. One of the wires is brown, so I wonder if it's related to what you were saying about supplementing the brown ground wire via a better connection.

Anything else you might want to add?

Your detailed info has been invaluable and I truly appreciate it Todd!

Thanks,

Roger

i have an 88 jetta and am haveing fuel problems. i replaced the sending unit and the fuel pump. the problem is still there, and there is a load hmmming sound coming from the fuel pump. Filter is new too. car is starving for gas, got just about a 1/4 of a tank. i beleive it is the transfer pump, can i put higher flow pumps on, any help?