No Power at the fuel pump - Hyundai Forum - Hyundai Enthusiast Forums


Hyundai Elantra While not much larger than the accent, the Elantra offers similar room, but a sportier look and feel, as well as more power.

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Old 01-08-2018, 10:05 PM
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Default No Power at the fuel pump

My daughter has an '07 Elantra that has been having fuel issues on and off for a few months. When the problem is manifesting itself you will try to start the car and it will turn over and run or sputter for 5 to 10 seconds then die. If it sits for a while it will start without any problems. The way I determined it was a fuel problem when the car would not start I used a little starting fluid to see if it would start and run for a few seconds, and it does. Because of the starter fluid test and the fact that it tries to run but then dies, I believe that the problem is with the fuel delivery system.

Because the problem has been rather inconstant and has frequently resolved itself by the time I get to where the car or it has cleared up while I have been trying to diagnose it, I have replaced the usual suspects. First I replaced the fuel pump relay since it is really easy and a very inexpensive fix and the car ran fine for about a month. Next I replaced the fuel pump the car again ran for about a month. This last time I was able to get to the car right a way and could hear that the fuel pump was not running so I pulled the seat and disconnected the fuel line. When I turned on the key I expected gas to spray all over the back but there was none. I think the next step is to test the wiring back to the fuel pump but I don't know what the pin-out for the wiring harness is.

Could someone help with the wiring scheme or with any other suggestions.
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Old 01-09-2018, 11:42 AM
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*** Update I have tested both wiring harnesses and I found that one of the pins has 12VDC for a few seconds and then it drops. I believe that I have power to the pump but I don't know if I have other problems with the wiring harness. I know a few of the leads are for the fuel gauge but I am not sure which ones. Also, If the fuel pump is removed from the tank, will it run. I know that I have been able to get them to run on other cars when out side of the tank.
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Old 01-10-2018, 06:43 AM
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When the key is turned to the on position, the ECU will turn power up the fuel pump for a few seconds.
If the engine is cranked then the ECU will supply a more constant power to the fuel pump

Usually, I will turn key to on and listen for the fuel pump to run
If it does then move on to see if it runs while cranking

If you want to see constant power at the fuel pump ...
At the fuel pump relay, use a paper clip to short out pin 30 and 87

Warning, be careful not to short out the other pins
One of them goes to the ECU and shorting them will fry the ECU
Which would cost you lots of money to fix
Heed the warning. Make sure you know what you are doing.
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Old 01-10-2018, 09:08 AM
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Quote:
Originally Posted by avisitor View Post
When the key is turned to the on position, the ECU will turn power up the fuel pump for a few seconds.
If the engine is cranked then the ECU will supply a more constant power to the fuel pump

Usually, I will turn key to on and listen for the fuel pump to run
If it does then move on to see if it runs while cranking

If you want to see constant power at the fuel pump ...
At the fuel pump relay, use a paper clip to short out pin 30 and 87

Warning, be careful not to short out the other pins
One of them goes to the ECU and shorting them will fry the ECU
Which would cost you lots of money to fix
Heed the warning. Make sure you know what you are doing.
After working on it for a few hours last night i think the problem may be the ECU. I have identified the pins going to the pump and know their functions. When I turn the key I get voltage on the correct pins, unless the fuel pump is connected.

I was able to put 12v from the battery directly to the pins on the pump and it works fine. So why does the voltage drop from the wiring harness when the pump is connected? When the pump is not connected then I have voltageon the wiring harness as expected.

I did notice that the positive wire going I to the harness had a companion wire spliced into it. What is that for and could it be the root of my problems?
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Old 01-10-2018, 12:02 PM
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The drop in voltage is sometimes due to corrosion at the wiring contacts
An initial voltage check with units off with give correct voltage readings
However, with the circuit loaded down the resistance in the line will rise to the point
Where the readings may be close to zero.

It is not unusual for car makers to add a wire going to the positive battery post
Nissan puts a whole set of fusible links on the battery post

So, the first things I would do is to clean up any terminals and grounding points
Engine grounding straps. Connectors, etc.

Note: be careful. you don't want to short something while doing this.
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Old 01-23-2018, 05:54 PM
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Default Resolved

So I finally used my AAA card to have the car towed to the dealer. They charged me $89 to diagnose the problem, which was a really good deal. It turns out that the issue was a bad Jbox (junction box) somewhere near the midpoint of the car. The box was about $600 for the and another $180 for the labor to replace it, not such a good deal. Anyway, it is fixed and seems to be running fine now.
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Old 01-24-2018, 10:30 PM
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Thanks for the update
Never thought of a bad junction box
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