Can a faulty fuel pump damage an engine

JSCHWEIGHARDT

MEMBER
2009 BMW 328
6 CYL
2WD
AUTOMATIC
68,000 MILES

It did not start one morning. The shop first did a compression test and found one cylinder to be low 95 psi vs around 200 for the others. They eventually determined the fuel pump was running hot and the ground wire got compromised and shorting out. They reset the codes and got the car running. So without replacing the fuel pump yet, the car runs fine for 2 to 3 minutes, then runs rough with loss of power. I was only able to drive the car a mile before it started losing power. They said I need a new engine. My questions is, could a faulty fuel pump really just be the issue? Would a car with low compression even run smooth for a few minutes? I'm getting a second opinion from BMW, but would love to know your thoughts. Thanks

5 Replies

SCGRANTURISMO

MECHANIC
4,897 POSTS

Hello,

Does your vehicle have a turbocharger or a supercharger on it? If so, then if your engine was under boost pressure and it went lean (not enough fuel) then yes, you can do catastrophic engine damage, but that's it. A problem with your fuel pump would not cause an engine to lose compression in a cylinder and wouldn't cause your engine experience bearing failure like that. Also a
fuel pump either works or it doesn't causing the vehicle to either run or not run. But having said that an extremely lean condition can cause engine damage. Please keep us informed as to how everything turns out.

Thanks,
Alex
2CarPros

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Tuesday, September 3rd, 2019 AT 2:55 AM

JSCHWEIGHARDT

MEMBER
3 POSTS

Alex - Thanks for the fast reply. So BMW found misfire codes and switched the coils and the problem followed the bad coil, so they suggested doing a full coil replacement. Work was done and car got a clean bill of health. So glad I got a second opinion, but I still am a little puzzled how the ground wire on the fuel pump then manifested into a coil problem, but happy with the final resolve.

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Tuesday, September 3rd, 2019 AT 4:48 PM

SCGRANTURISMO

MECHANIC
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Hello again,

Funny how that happens, huh. Glad to hear about your vehicle.

Thanks,
Alex
2CarPros

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Wednesday, September 4th, 2019 AT 12:54 AM

JSCHWEIGHARDT

MEMBER
3 POSTS

And now for the rest of the story. So I said I was puzzled how the fuel pump ground wire issue disappeared and that replacing the coils fix the issue. Well a few days after picking up the car from the dealer and driving it around, one morning the car didn't start again.
So I decided to take a look at the fuel pump, and to my surprise when I pulled the connector the ground lead was black and the female barrel connector was fused to the male terminal.
So the first shop was right about the ground, but I did not have a compression issue and need a new engine. For the few days the car ran, it had plenty of power, no hesitation and idled fine.
I found a used pump on ebay with a connector and I plan to repair the connector since the pump is good.
One last note, I did see that BMW did have a recall because of bad wiring and referenced the crimping was not done correctly, but only the X and 6 series was included, not for the 328i. I personally feel this defect falls into the same recall issue. I'm going to see if the dealer agrees and maybe I get a new pump and a higher quality wire harness.

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Friday, September 13th, 2019 AT 7:28 PM

SCGRANTURISMO

MECHANIC
4,897 POSTS

Hello again,

Yes, that would cause like a brown out in your house. He goal of any electrical circuit is to dump all available voltage across the load, in this case the load is the fuel pump. This falls into one of Ohm's laws that are so cool on automobiles. Ohm's law states that if one of the three parts that make up electricity is constant, which in automotive applications there is always one constant(12.6 Volts-Battery Voltage) and one of the last two goes up(Resistance-The connector got melted causing unwanted resistance) then the last part(Amperage/Electrical Flow must go down proportionally). If there was any metal part of the positive wire that would have touched the negative terminal it would have caused a short to ground and the fuse would have blown. Anyway, good job. We are happy to hear you got it fixed, and good luck at the dealership.

Thanks,
Alex
2CarPros