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Discussion Starter · #1 ·
About a month ago, fuel pump was replaced by repair shop due to car will not start at all. Car seems to be working fine after the work done for about 3 weeks. One day of last week, car will not start immediately, it had to be cranked a couple times so it can start. It happens all the time when i leave the car off more than 5-10 minutes. If I stop the car and start right after, it starts quickly. Anyway I called the same repair shop, they told me battery may be started dying. I measured Voltage on the battery during cranking it goes down to 11V and goes back up to 12.9V after car starts. I have replaced the battery with the new one for precautionary.That did not fix the problem. Does anybody Know what else may be the problem with this? THANKS
 

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This sounds like the new fuel pump is bad too. A classic example of a failing fuel pump/regulator unit is needing several attempts to start the car. When you crank the car power is applied to the fuel pump for only a few seconds. Then the power is removed until the computer detects that the car has actually started & achieved a minimum RPM. It then re-enables the fuel pump. When the pump/regulator fail powering the pump initially increases the fuel line pressure to the minimum needed to force fuel into the injectors & start the car. When power is removed from the pump the regualtor & pump check valve are supposed to hold the fuel pressure in the lines. But it sounds like yours are allow the pressure to bleed off almost immediately. This is why a 2nd or 3rd attempt results in starting the car. The quicker you try to restart the car after each failure increases you odds of getting the car to start. This is because the fuel pressure will be higher the sooner you try to re-start. When power is applied to the pump again if it has sufficient ability to raise the pressure to the minimum start pressure the car starts. But I think you need to take the car back to the service center where the pump was replaced. Because I think the new pump is bad.

Note that I'm not sure if the pressure regulator is part of the fuel pump assembly on the Sonata. I believe it is but I don't know for sure. In most modern cars the pump & regulator are a combination unit located inside the fuel tank. It's a hard enough job to do once, you don't want to do it twice. So these are regularly replaced as a combined unit.

If the service center replaced the pump only & not the regulator then it could be that the regulator was the faulty part all along and it was temporarily masked by the new pump. But the service writer at the service center will know.

Good Luck
 

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What EXACTLY was replaced ? If they replace just the "fuel pump" in the middle of the pump module... then you likely spinning your wheels.

Problem with NF fuel pump is the old pump draw too much current, and overheat the lugs related to getting electric from outside of tank to inside of tank to run the pump.. This overheat causes large voltage drop across the connection, thus we install new style pump module assembly, and related tube.

Inside the tank, where the fuel pump pigtail plug into bottom of cover, look at the connector (unplugged) for sign of brown/black plastic from overheat.. look at terminal at the bottom of cover where connector plugs in.. is it all brown/black from overheat ??
 

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Discussion Starter · #4 · (Edited)
First Thanks for the reply, I appreciated. Answer to your question is whole assembly was replaced. It was used assembly however I asked them to replace new pump with a used assembly. Repair shop has showed me the old assembly removed from the car, there a was burnt connector between pump and assembly which was the main cause of the original problem. This required repair shop to replace the whole thing. New one was very costly and I went with used assembly with a new pump. Thanks again. I am looking for a way to pressure test the pump assembly to see where the problem is and to see it can be repaired.
I will need to take it to repair shop to see if the same connector has started problem. Should I go with whole new assembly rather than used one if it turns out be the fuel pump assembly is the problem once more?
 

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Pull it out and check for burnt terminal again,, volt drop test across the connector be of value too..
 
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