Buick Century:

Fuel pump is humming, intermittent crank no start?

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# 1  1/15/2016 6:07 AM

eleet313
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Registered: 1/15/2016
Posts: 5

Fuel pump is humming, intermittent crank no start?

2004 Buick Century 3.1

Car wouldn't start today unless I gave it some gas.  As soon as I let off the throttle it crapped out. Started it again and kept throttle down for a little bit and it stayed running when I let off throttle after that.  This keeps happening more often now. Sometimes it fires up on its own but there is always this whining or high pitch humming which I believe is the fuel pump. Key on engine off it starts whining and continues entire time car is running.Today when it crapped out after I got it started I noticed the darn service engine light came on. I took it to Auto Zone for a scan and they only have the little code reader. It was a P0420 code. Please tell me the cheapest way to fix this! Thanks guys.

Is there any way it's just the filter? Or maybe the fuel pump. I hope it's not expensive

Last edited by eleet313 (1/15/2016 6:10 AM)

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# 2  1/15/2016 4:51 PM

TechHelp2
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Registered: 11/24/2009
Posts: 1305

Re: Fuel pump is humming, intermittent crank no start?

The P0420 is related to the efficiency of the catalytic converter. The PCM determines that the efficiency of the catalyst has degraded below a calibrated threshold. 

This can also be related to the oxygen sensor not functioning properly and could set the code. The fact that you have been starting the vehicle so many times could be setting up conditions to set the P0420.

Using a good scan tool can help you check the efficiency of the oxygen sensors and if they are functioning properly.

The other condition you have is the stalling. The throttle plate needs to be cleaned of carbon (they call it coking). If the throttle plate is not clean it makes the Idle Air Control Motor work beyond the limit it can work and may even get stuck because of all the carbon. If the IAC motor can not move properly it will cause a stalling problem.

Cleaning the throttle plate and replacing the Idle Air Control motor (IAC motor) can help fix this problem.

Sometimes the high pitch whine in the fuel tank could be normal or could be the indication of a fuel pump going bad.

A certified mechanic can determine if the fuel pump needs to be replaced. He can also check the condition of the oxygen sensors with a professional scan tool to see if they need to be replaced.

I would first clean the throttle plate of all the carbon and change the Idle Air Control motor to at least see if the stalling goes away then address the other issues after that. Then have the code cleared from the computer and see if the code comes back.


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# 3  1/16/2016 2:17 AM

eleet313
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Registered: 1/15/2016
Posts: 5

Re: Fuel pump is humming, intermittent crank no start?

Thanks for your advice I will start with that. Its free and it wont hurt to clean anything. Also I forgot to mention the Fuel gauge does not work either it usually will read that it is empty but sometimes goes to full. Never works properly. Do you think that is more evidence of a bad fuel pump? The fuel level sensor is contained within the pump right?

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# 4  1/16/2016 2:44 AM

Administrator
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Registered: 9/27/2008
Posts: 1286

Re: Fuel pump is humming, intermittent crank no start?

A loud whining from the fuel tank is the fuel on its way out. The hard start and stall are most likely also due to the bad pump. The fuel pressure must be tested to confirm.

The gas gauge problem and cat converter DTC are probably unrelated.

The gauge issue can come from a bad sending unit in the tank, problem in the instrument cluster, or a bad connection between the two.

P0420 is almost always a bad cat, but on rare occurrences caused by a faulty secondary O2 sensor.

Start with a fuel pressure test, and if confirmed, replacement the pump. Wanna get the thing running correctly first. The cat converter will be the most expensive of the bunch.


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# 5  1/24/2016 11:05 PM

eleet313
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Registered: 1/15/2016
Posts: 5

Re: Fuel pump is humming, intermittent crank no start?

So my girlfriend told me it just stopped running while she was driving yesterday. She said it sounded like it was running out of gas. So I went and replaced the $200 fuel pump and its running again now. But the issue with starting still persists. It won't run on its own until its warmed up. I cleaned the throttle plate, filled the tank, used some injector cleaner (which works nicely in combo with the new fuel pump smile) but it still stalls without some extra throttle when starting. Hoping IAC is cheap. Going to check now. What about MAF? If you have any other tips they are greatly appreciated. I just don't get it. It runs GREAT. But doesn't start properly? Thanks!

Last edited by eleet313 (1/24/2016 11:14 PM)

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# 6  1/25/2016 5:26 AM

TechHelp2
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Registered: 11/24/2009
Posts: 1305

Re: Fuel pump is humming, intermittent crank no start?

If it runs great when it is warmed up and is hard starting and stalls when cold then the most likely problem would be the IAC motor.

Get back to us with your results if needed we can diagnosis the problem further.


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# 7  1/25/2016 7:33 PM

eleet313
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Registered: 1/15/2016
Posts: 5

Re: Fuel pump is humming, intermittent crank no start?

Well sometimes it starts when cold. But it also sometimes doesn't start when warm. Its completely random, but extra throttle always ensures it starts however it will stall when throttle released initially I usually rev for about 30-45 seconds and then it idles completely fine. When it does start without throttle input it also idles fine. It always idles fine once it is actually running. It's just a mystery when I turn the key if it will fire up and idle or if I will have to give it some throttle before it will idle.  Also I unfortunately have no tachometer so I am clueless to engine rpm's.  Anyways I tried cleaned up IAC before I buy one and the first attempt at starting was successful. I shut it off and tried to start again and it cranked and wouldn't start on its own again.  My question is...Is there something with the ignition when I turn the key that may not be communicating the need for air/fuel or throttle regulation?  OR Since the fuel pump is 1 day old now. Is there maybe an issue (maybe fuel filter/ injectors) getting proper fuel pressure after it leaves the pump? None of it makes sense because it's only when I turn the key to start it. But otherwise it idles and runs all day just fine. Does TPS do anything when turning the key? Any idea I come up with gets thrown out because it really runs great and idles fine so I know its getting everything it needs.  Sorry guys. I know this one is a pain in the ass at least for me it is lol. Thank you so much.

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# 8  1/26/2016 12:39 AM

eleet313
New member
Registered: 1/15/2016
Posts: 5

Re: Fuel pump is humming, intermittent crank no start?

New IAC is in. When I compared the two I noticed the pintle was fully extended on the old one. Meaning it was probably stuck almost completely closed. So throttle input was needed because not enough air was passing through the bypass when starting. Last 5 starts have been flawless. THANKS GUYS! I will be back in the future I am sure about that.big_smilebig_smile

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# 9  1/26/2016 12:52 AM

TechHelp2
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Registered: 11/24/2009
Posts: 1305

Re: Fuel pump is humming, intermittent crank no start?

We are glad we could help. Thank you for using RealWorldAutomotive.


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