Fuel pump relay - Pump sound

CaptainXL

Original poster
Member
Dec 4, 2011
2,445
Hey, I have been noticing that ever since I bought my truck that the fuel pump sounds kind of weird like the pressure has been going up and down. So today I swapped the fuel pump relay and now it sounds a lot better. You know that characteristic whirling sound when you turn the key on? Just thought I would throw that out there. Kind of just looking at different things which would be causing it to stall in hot weather at idle.
 

gunrock

Member
Mar 27, 2012
22
So did the sound from your fuel pump before the relay swap, when priming, sound like a "warbly" noise or maybe a dead or muffled turkey? :smile:

Also, did your tank vibrate badly from it?

My plight is a long story, and will be posting soon, after I troubleshoot what I can thanks to some helpful videos from May03LT. This is my 2nd AC Delco pump in a year, and the original did it as well, but figured I'd ask about yours to see if its a similar situation.

The fuel pump noise (again, only hear it when you turn key to prime it OR once in a while when shutting down truck) occurs during extreme heat days, 90 plus degrees, or hot 85 degree plus days and towing about 3200 pounds. Driving or towing in cool weather I never hear the pump, other than the normal noise pumps make when they energize.

I don't seem to have any other symptoms--never notice any power loss or mpg loss or stalling.

gunrock
 

CaptainXL

Original poster
Member
Dec 4, 2011
2,445
gunrock said:
So did the sound from your fuel pump before the relay swap, when priming, sound like a "warbly" noise or maybe a dead or muffled turkey? :smile:

Also, did your tank vibrate badly from it?

gunrock

My tank never vibrated but i did notice a warbling sound.
 

gunrock

Member
Mar 27, 2012
22
CaptainXL said:
My tank never vibrated but i did notice a warbling sound.

Hmmm, I was under the impression a relay is good or it isn't? I did do three of the four tests for ground and voltage that was provided on youtube from a user here on gmtnation and they checked fine. I didn't do power to the pump because I wanted to order a fuel pressure tester.

I swapped the high beam? relay with the fuel pump relay since they are the same to see what happens.

I used to have a recording of it...if I find it I will post for comparison/reference.

gunrock
 

The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
gunrock said:
Hmmm, I was under the impression a relay is good or it isn't?
Rarely, a relay can have a short internal to its coil, that reduces its sensitivity and can cause erratic actuation. More often, the power contacts can get pitted from micro-arcing like old-time distributors could get bad points. That makes the power contacts erratic. The condenser on old distributors was there to reduce that pitting, but modern relays don't have the same sort of protection. In my day job, I do failure analysis sometimes, and relays (most of mine are subminiature and need microscopes to look at) have many odd failure modes you might not think were possible.
 

novajoe

Member
Oct 8, 2012
82
Any further info on this? Did you find the problem?

Today after a five hour drive my fuel pump started to make the warbling noise during the prime only. (130+K miles on pump) Fuel pressure is good so the pump is working. I am just checking to see if there is anything else that may cause this or is it just the first signs of a dying fuel pump.
 

gunrock

Member
Mar 27, 2012
22
novajoe said:
Any further info on this? Did you find the problem?

Today after a five hour drive my fuel pump started to make the warbling noise during the prime only. (130+K miles on pump) Fuel pressure is good so the pump is working. I am just checking to see if there is anything else that may cause this or is it just the first signs of a dying fuel pump.

You know what? I never did find out. As a matter of fact, I ran it for about four hours on a cool day last September and not once did it make the warbly noise. Same as you, fuel pressure was fine and no performance issues.

I wanted to try and measure voltages on the pump (to rule out faulty wiring), but never made it that far. I was also wondering if it was some sort of venting issue since it only happened on hot days-but that is pure speculation...I am not a mechanic or even probably familiar enough with the system to make that statement; just my personal thought.

The only advice I can offer after spending a lot of money having a mechanic look at it (and it was only half done, since the issue was not fixed and they did not troubleshoot) and watching May03LT's videos and reading posts are:

1)The pump has 130K on it, it's probably time to replace it anyway.
2)Get an OEM pump.
3)Make sure the mechanic troubleshoots the issue and doesn't throw parts at it--check wiring, measure voltages, and anything else they can do with the tank off since you already paid the labor to have it removed. :smile:
4)Maybe replace the fuel filter, too? Especially I think the later years, the filter is a lot harder to access?

I am sure someone might offer something a little more useful, that's just my experience and I am not a mechanic. Good luck it was frustrating. I ended up trading it in for a Ford Expedition....I already miss my Trailblazer...it seemed more comfortable and I have already paid to rebuild the rear differential, a rear wheel bearing and front axle seal. Plus, it has a bunch of other minor "known" issues I need to fix someday....and my biggest fear....Spark plugs--it's a 2005 and I guess that 2nd gen 5.4 engine is known for plugs getting stuck in the block, yay!

If you do find a solution, I'd be curious to know what it is.

gunrock
 

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