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Martin
Martin, auto electrical
Category: VW
Satisfied Customers: 564
Experience:  South African Trade Diploma in Auto Electrical
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84 rabbit: 1.8L..fuel pump relay is running..running hot..wiring

Resolved Question:

My vw 84 rabbit 1.8L wolfsburg edition has a reoccuring problem. It's fuel pump relay is running hot and the fuse will burn out. Fuel pump was replaced, wiring replaced. Could the relay be faulty? Please advise.

Laszlo
Submitted: 3 years ago.
Category: VW
Expert:  Martin replied 3 years ago.
Hi, my name is XXXXX XXXXX I am at your service to assist with your VW problems.

I had the same problem a couple of years back on a VW Jetta. The primary pump was the fault on that car but, as the cars in South Africa are not the same, I ask that you check whether your car has a primary pump in the fuel tank, which might be the culprit. All the other work which you have done cancels out most of the other possibilities. You can, however, open the fuel pump relay and check the condition of the contacts, to establish that they are not making bad contact and creating the heat. If necessary, replace the fuel pump relay. Should you require further assistance do not hesitate to ask.
Customer: replied 3 years ago.

Thank you Martin.

I will do as you said and hopefully this will help.

Expert:  Martin replied 3 years ago.
Hi,

Please keep me up to date with what you find, and hope you get everything sorted out.

Regards,
Martin.
Customer: replied 3 years ago.

There is one fuel pump and that is what was replaced when this problem began to occur. As much as I can tell there is no burn marks or other visible signs on the fuse box or the contacts of the relay. Can you specify the ratings of the relay; ie how many amps, watts, ohms etc. should it be, maybe it is a wrong relay being used?

Please advised.

 

Thanks,

Laszlo

Expert:  Martin replied 3 years ago.
Hi Laszlo,
The fuel pump should not use more than 10 ampere and the fuse should be a 15 ampere. Standard multi purpose relays all have a standard 30 ampere rating. The Bosch relay contact is normally over designed and can actually handle more current flow, there are some relays that state 30 ampere but when one compares the contacts with the Bosch relay then you see how badly they are made. The fuel pump relay is being controlled by the computer, it will only switch on when there is an rpm reading from the ignition coil. The fuel pump relay contacts can actually handle more current than is stated on the casing.
Regards,
Martin.
Customer: replied 3 years ago.

Thank you for the specs. I wonder if you could speculate / theorize why the relay and the fuse are getting hotter if i drive the car faster (if I go on the highway-60-70 miles/hour it gets real hot but if I go less then 45 miles/hour the relay gets only warm, the fuse only lukewarm)? What would you do? I spent a lot of money on this problem,and I am getting a little frustrated because the car is not dependable.

Thanks for the help.

Laszlo

Expert:  Martin replied 3 years ago.
Hi Laszlo,
When the car is being driven at a higher speed the computer emits the full current flow on the system to let the pump run at maximum speed. Personally I have never encountered this problem before, as it is very rare. My first thoughts are that the computer might be the culprit, but I shall do some studying and let you know.
Regards,
Martin.
Expert:  Martin replied 3 years ago.
Hi Laszlo,
What I know so far, have someone assist you with this test, take the car for a run and measure the volts and ampere flow while driving the car on the open road. The volts must not go higher than 14.5 and the current flow not more than 10 amperes. If the volts go higher first check that the alternator is not over charging. The voltage on the alternator should also read 14.5 volts, anything higher means the voltage regulator is faulty. If the voltage on the alternator is fine, and between the positive and negative terminals on the battery, but the voltage on the fuel pump relay contacts is higher then check the earth connection between the battery and the body, and that the earth connection between the body and the computer is 100% good. If all this checks remove the computer and open it and check for any bad soldering joints and/or simply replace the computer. This is what I have learnt so far but should something not be clear to you do not hesitate to contact me.
Regards,
Martin.

Martin, auto electrical
Category: VW
Satisfied Customers: 564
Experience: South African Trade Diploma in Auto Electrical
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