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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Powertrain and Drivetrain Discussions > N54 Turbo Engine / Drivetrain / Exhaust Modifications - 335i > Can a faulty fuel pump foul plugs?



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      08-26-2008, 06:51 AM   #1
Bubbles
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Can a faulty fuel pump foul plugs?

Can someone explain this scenario in layman terms?

I was chatting with a Tech yesterday about the possibility that our faulty fuel pumps have been fouling plugs. He now pulls the plugs when a car comes in with limp mode issue and has performed several plug swaps this month. He did admit the swap was merely a band aid rather than remedy.
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      08-26-2008, 07:04 AM   #2
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Quote:
Originally Posted by Bubbles View Post
Can someone explain this scenario in layman terms?

I was chatting with a Tech yesterday about the possibility that our faulty fuel pumps have been fouling plugs. He now pulls the plugs when a car comes in with limp mode issue and has performed several plug swaps this month. He did admit the swap was merely a band aid rather than remedy.
Bubbles, going lean can definitely foul plugs. If you pull a plug it would look white in this scenario and would need to be replaced.
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      08-26-2008, 09:11 AM   #3
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Originally Posted by Former_Boosted_IS View Post
Bubbles, going lean can definitely foul plugs. If you pull a plug it would look white in this scenario and would need to be replaced.
I may have misunderstood the Tech, but my understanding from our conversation was that it wasn't a "running lean" issue. Is there any other possibility of fouling the plug with a faulty fuel pump?
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      08-26-2008, 10:13 AM   #4
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I'm certainly no expert, but I fail to see how a faulty fuel pump would cause plug fouling. That would come either from too rich a mixture, or incomplete combustion. I would imagine a faulty fuel pump would cause a decrease in pressure resulting in a lean condition as already pointed out. A lean condition can overheat the engine and cause plug damage, but not fouling in the sense that I'm familiar with.
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      08-26-2008, 10:21 AM   #5
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Quote:
Originally Posted by techforge View Post
I'm certainly no expert, but I fail to see how a faulty fuel pump would cause plug fouling. That would come either from too rich a mixture, or incomplete combustion. I would imagine a faulty fuel pump would cause a decrease in pressure resulting in a lean condition as already pointed out. A lean condition can overheat the engine and cause plug damage, but not fouling in the sense that I'm familiar with.
Leaned A/F on plugs can definitely result in damaged plus and misfires. Maybe the tech was "dumbing" things down?
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      08-26-2008, 10:25 AM   #6
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Quote:
Originally Posted by Bubbles View Post
Can someone explain this scenario in layman terms?

I was chatting with a Tech yesterday about the possibility that our faulty fuel pumps have been fouling plugs. He now pulls the plugs when a car comes in with limp mode issue and has performed several plug swaps this month. He did admit the swap was merely a band aid rather than remedy.
A poorly performing fuel pump can cause spark plugs to foul. The plug will have a dusty layer of black carbon deposits. The reason this happen is that the pump is not performing optimally which leads to poor atomization of the fuel and incomplete burn. You will notice that your gas mileage will progressively get worse because the engine is less efficient.
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      08-26-2008, 12:30 PM   #7
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Quote:
Originally Posted by Former_Boosted_IS View Post
Leaned A/F on plugs can definitely result in damaged plus and misfires. Maybe the tech was "dumbing" things down?
Now that's insulting

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Originally Posted by Orb View Post
A poorly performing fuel pump can cause spark plugs to foul. The plug will have a dusty layer of black carbon deposits. The reason this happen is that the pump is not performing optimally which leads to poor atomization of the fuel and incomplete burn. You will notice that your gas mileage will progressively get worse because the engine is less efficient.
Orb
So basically the injector fails to make a "good spray" which causes a carbon build up and eventual fouling of the plugs. Good info Orb, thank you.
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      08-26-2008, 05:33 PM   #8
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I would ask him what codes he is seeing when the cars come in. If a plug is bad, wouldn't it throw a cylinder misfire code?
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      08-26-2008, 07:07 PM   #9
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Originally Posted by Bubbles View Post
Now that's insulting



So basically the injector fails to make a "good spray" which causes a carbon build up and eventual fouling of the plugs. Good info Orb, thank you.
This is more or less correct and is based on the control system of the engine (it will not allow a lean condition if at all possible). The carbon build up in this case wouldn't be normal. It will be like the carbon you find in the exhaust pipe which is dry and powdery. It can cause performance problems that will not be evident to the end user because of the control system.

I'm getting a new fuel pump (3rd generation) and new plugs next week because this is the problem I have now.

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      08-26-2008, 07:47 PM   #10
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Quote:
Originally Posted by Orb View Post
This is more or less correct and is based on the control system of the engine (it will not allow a lean condition if at all possible). The carbon build up in this case wouldn't be normal. It will be like the carbon you find in the exhaust pipe which is dry and powdery. It can cause performance problems that will not be evident to the end user because of the control system.

I'm getting a new fuel pump (3rd generation) and new plugs next week because this is the problem I have now.

Orb
So is the wait for new fuel pumps over or are you the exception?
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      08-26-2008, 08:17 PM   #11
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So is the wait for new fuel pumps over or are you the exception?
The 3rd generation pumps are hard to get but i found one through my own efforts (special thanks to one of the vendors on this site). I going to get reinversed for everthing it seems an should have car back to full heath next week. I hate the car with the newest stock software.

The 3rd generation pumps are hard to get but I found one through my own efforts (Special thanks to one of the vendors on this site). I am going to get compensated for everything it seems and should have car back to full heath next week. I hate the car with the newest stock software.

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