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2002 chevy trailblazer_lt
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Discussion Starter #1
New battery about a month ago. Started on first try, like usual. Now, when ignition is turned on there is no 2-3 sec hum or buzz. I assume that's the fuel pump not priming.
 

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2002 chevy trailblazer_lt
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Discussion Starter #3 (Edited)
I swapped #41 fuel pump fuse with Hi beam fuse (I got from a video post on fuel pump testing on this site
) and no go. Gonna test for power on the fuse pin cavities. I have a multi meter, but am not very experienced with it's use. I know + and - , but what do I set the meter to test? Don't wanna blow anything...
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I just jumped and energized something in the throttle control area. No fuel pump hum from below the driver's seat. How do I locate the wire from the box to the pump on the fuel tank?
 

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This part scares me: "I just jumped and energized something in the throttle control area. "

Many 'things' under the hood and other places will NOT take 12VDC nicely!

Indiscriminately powering up 'something' near the throttle body is .... I got nothing here......

[gone] [outta here] [sleeping]

<< Hey mods - we REALLY need some colors here for our posts - this one needed RED >>
 
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2002 chevy trailblazer_lt
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Discussion Starter #5
It wasn't indiscriminate. I jumped poles on the fuel pump relay port (#41) as per the video that I got from TrailVoy (see above). I re-posted on this thread so that others might find it useful. I apologize if that was unclear.
 

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2002 chevy trailblazer_lt
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Wait...2002 LT is supposed to have a fuel pump hum after initial power on/precrank? I've never heard it on mine. lol...is bad thing?
 

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They only hum when they don't know the words............

But seriously - some make noise - some don't - then again, there's the 'perception' part of it if you are deaf and you know who you are - your wife tells you you don't hear her any more!
 

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2006 chevy trailblazer_ls_ext
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Have you checked your oil pressure sending unit? GM typical ties the fuel pump into this sending unit. In case of a serious accident the oil pressure drops to 0 when the engine stops, shutting down the fuel pump stopping the flow of fuel. If the sending unit goes bad, it can shut down the fuel pump too.
 

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2005 buick rainier
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I might be missing something hear but is the vehicle a no start? The ECM needs to see a crank or running input to energize the fuel pump. Just turning the key to the on position will not energize the fuel pump.
 

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2002 chevy trailblazer_lt
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Discussion Starter #10
Have you checked your oil pressure sending unit? GM typical ties the fuel pump into this sending unit. In case of a serious accident the oil pressure drops to 0 when the engine stops, shutting down the fuel pump stopping the flow of fuel. If the sending unit goes bad, it can shut down the fuel pump too.
I have not. where is it located? How do I test it?
 

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2002 chevy trailblazer_lt
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Discussion Starter #11
I might be missing something hear but is the vehicle a no start? The ECM needs to see a crank or running input to energize the fuel pump. Just turning the key to the on position will not energize the fuel pump.
Moving the ignition switch to the RUN position would cause a short buzz from beneath the driver's seat of 1-2 sec. No buzz. Engine cranks fine, just no fire.
 

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2005 buick rainier
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The under hood fuel pump relay #41 is fed power from the ECM in the ON position for 2 seconds or when cranking / running. The relay closes and the 12v power from ECM B fuse powers the fuel pump. Fuel pump relay needs to "click" when energized. Before most mechanics pull out the scan tool, test lights etc. - pull out a soft hammer and rap on the bottom of the fuel tank while cranking if a fuel pump is going out this will many times get them spinning again.
 

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I might be missing something hear but is the vehicle a no start? The ECM needs to see a crank or running input to energize the fuel pump. Just turning the key to the on position will not energize the fuel pump.
Incorrect.

As you pass the RUN position and turn the lockswitch to START, the fuel pump has already been triggered to run to get the engine ready to start as soon as ignition and rotation start.

IF the engine does NOT start - or you don't go all the way to CRANK --- THEN the pump will time-out and shut down.

We must be careful to inform people who may not know any better, the actual facts.

TBH: I make a lot of mistakes too.... just sayin'............
 

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Incorrect.

As you pass the RUN position and turn the lockswitch to START, the fuel pump has already been triggered to run to get the engine ready to start as soon as ignition and rotation start.

IF the engine does NOT start - or you don't go all the way to CRANK --- THEN the pump will time-out and shut down.

We must be careful to inform people who may not know any better, the actual facts.

TBH: I make a lot of mistakes too.... just sayin'............
I corrected my initial response concerning the initial KOEO 2 second prime in my response right before your post. Mitchel On Demand actually doesn't clarify initial KOEO priming. If you want to sling a little mud my way for a little misinformation fine but when I visit these DIY forums they are chalk full of mis-information & mis-guided diagnostics.
 

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2004 chevy trailblazer_lt
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I understand that. I own an ‘04 without working gages. Lol.
I don’t believe I’ve EVER heard the fuel pump humming. On real cold winter days there’s a whining humming for a few seconds in initial start up that could be the fuel pump I guess.
I was wondering if the OP got his issue figured out. I would by start looking at fuses/relays.
 

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Discussion Starter #20
I understand that. I own an ‘04 without working gages. Lol.
I don’t believe I’ve EVER heard the fuel pump humming. On real cold winter days there’s a whining humming for a few seconds in initial start up that could be the fuel pump I guess.
I was wondering if the OP got his issue figured out. I would by start looking at fuses/relays.
Had to retrieve my floor jack from a forgetful friend... Got the rear end up on jack stands and cider blocks under tires. Relay working. Jumped relay plugs (lower right to upper left); no hum, no start when cranked. Can't get a meter on the plug at the relay without dropping tank, so...
The good news is the vehicle is at 307K, so got mu' monies worth. Bad news is good options run about 300+ scoots.
Any advice?
 
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