Mercruiser 5.7 Whining Noise - Intermittent and Independent of rpm

[thumpar]

Better put a decal set on that flame arrestor cover! That BOX down by the motor is your Gen II fuel pump & cooler. The P/S cooler on that engine straddled on the *** end of the engine.

I was wondering if it could be the fuel cooler/pump but I didn't think carbed motors had them.

 

[DuncanDonut]

Thanks for the input. The picture came from the internet. Mine is a 5.7 EFI. Sorry for the confusion. It seems that the whine/vibration is coming from the fuel pump/cooler. Any thoughts on why it takes about 2 minutes after the engine is started to start whining? And why the pitch changes when I trim the tabs up and down? Does that point to an external vibration issue (perhaps against the hull) rather than an internal whining noise?

 

[alldodge]

It seems that the whine/vibration is coming from the fuel pump/cooler. Any thoughts on why it takes about 2 minutes after the engine is started to start whining?

Being it starts whining a couple minutes after start, then its the fuel pump not the cooler. The cooler is item 8 and the pump is item 3 and both are mounted together. Taking a bit of time before it starts leans me toward the pump is having trouble pulling fuel thru the tank and filter (anti siphon valve, lines and filter) or the pump is going out, or your sucking air from a leak.

http://www.mercruiserparts.com/bam/subassembly/31896/2337/90

If the filter is clean and the anti siphon valve is not sticking, and there is no air leak, then check fuel pump pressure

 

[Pete104]

Check AllDodge suggestions. Something is making the pump struggle. But the clamp in the bilge you found for the P/S steering hoses tells me that someone has spent some time down there already. Can't say why but possibly an aftermarket pump. I think you have already run it on a remote tank and got the same results. Correct?

Don't know/very frustrating!

 

[DuncanDonut]

Fellers - thanks for all your diagnostic assistance. I just got back from the boat. Now I'm getting discouraged. It is definitely the fuel pump. I have not run on a remote tank, yet. Not even sure how to do that.

Five questions.

1) The boat runs fine. Am I tempting fate to take it out?
2) Are there options other than replace it? Clean out the screen? Fuel treatment? Other?
3) How difficult is it to replace myself? I suppose I remove the alternator to access the filter - then...
4) What is the purpose of the CoolFuel item in the photo below. Would changing that filter help?
5) Is there anything else I need to do of a diagnostic nature?

 

[thumpar]

The cool fuel is to help keeping the engine from vapor locking. How loud is the whine? I have the VST version and it makes a whine but it is not terribly loud and has always done it. Anymore I don't notice it.

 

[Pete104]

That ain't even the fuel pump! That's water seperator filter.
The purpose for "cool fuel" in theory; keep fuel cool as when temp rises it begins to seperate is a fast answer.
You may just have a "whiney" pump.

 

[thumpar]

That ain't even the fuel pump! That's water seperator filter.
The purpose for "cool fuel" in theory; keep fuel cool as when temp rises it begins to seperate is a fast answer.
You may just have a "whiney" pump.

The cool fuel does have a booster pump in it just like the VST does. They run 2 pumps. One for low pressure and another for the high pressure for the fuel injectors.

 

[DuncanDonut]

I noticed the fuel pump whining about a month ago. It was intermittent at the time. Now it is continuous, so it seems to be a worsening condition. It may be getting worse because I am using the boat more than its previous owner. I don't know how well he maintained his fuel integrity. I have been told that stale fuel can result in formation of "shellac" balls that can clog filters and screens. Would fuel treatment help reverse this process? If so, which ones would you recommend? I put Stabil into the gas about a month ago. Could that have exacerbated the problem?

It is loud enough to hear with the hatch closed at idle. I don't notice it when cruising.

I feel the need to do something. Do I have any credible options besides replacing the fuel pump? Thanks again for everyone's input.

 

[alldodge]

1) The boat runs fine. Am I tempting fate to take it out?
2) Are there options other than replace it? Clean out the screen? Fuel treatment? Other?
Would changing that filter help?

If the boats fuel pressure is reduced, your motor may run lean. A lean running motor will destroy it self over time.
If the pump is OK but having trouble getting fuel due to a restriction in the line, a fitting or fuel filter, given enough time the pump will be damaged.

Yes, changing the filter would help if it's clogged or the seal is leaking. If the filter has not been changed this season then do replace it. The plastic cover is removed to gain access to it

3) How difficult is it to replace myself? I suppose I remove the alternator to access the filter - then...
4) What is the purpose of the CoolFuel item in the photo below.

The hardest part in replacing the fuel pump is getting at it. The cool fuel module is on the port side down low and behind the motor mount. The plastic cover comes off easy with a couple plastic clips. Once off you can see the fuel pump and the cooler tube. As Pete104 mentioned your pic is the fuel filter

5) Is there anything else I need to do of a diagnostic nature?

You will need a high pressure gauge and a fitting to check the fuel pump output.





Don't know if a booster pump was added but your motor did not come with one. If one was installed it will be next to the fuel filter.

 

[Scott06]

If you verified that nothing upstream is restricting fuel flow I think your options are ear plugs or replace the pump. It may just be a loud pump and not an indication of impending failure. Have you measured the output pressure? If in spec may just be a loud pump. If it's getting louder may indicate a dying pump. Most likely it is more of a nuisance than anything else.

 

[Pete104]

The cool fuel does have a booster pump in it just like the VST does. They run 2 pumps. One for low pressure and another for the high pressure for the fuel injectors.

Right, but not all. There is a serial # group that ran the boost pump. And this engine just may be close to that serial group. But it runs good, leave it.

 

[DuncanDonut]

Pretty much resigned to replacing the fuel pump, especially since the whine has gotten noticeably worse over the last month. It is 20 years old so it is probably near it's life span. I am going to remove the alternator in the morning, remove the plastic casing and get a part number on the pump. I've been told that external fuel pumps do not normally have screens on the inlet so it is not likely to be a simple fix like cleaning a screen. I have a friend standing by to help me find a replacement pump.

 

[NHGuy]

An ounce of prevention is worth a pound of cure.

 

[DuncanDonut]

Another day of bilge diving. Removed the alternator and the plastic casing around the fuel cooler and pump. The casing was not closed well. I turned on the engine and felt the fuel pump. It was NOT hot to the touch making me think that it may simply be a whiny fuel pump instead of a failing fuel pump. At any rate, it is beyond my expertise to replace. My friend and I felt very fortunate to get the boat back to together today given the tight quarters (I am 6' 3" and 220 lbs - I could not have done it without my smaller and more agile friend). We put a zip tie around the plastic case to keep it closed and it improved the volume of the whine noticeably, but it is still there. I still want to check the fuel pressure. If the pressure is okay, I will probably let it go for a while.

I could not find a part number for the fuel pump but I have the engine serial number and the dimensions on the fuel pump. The engine serial number is 0K190291. The fuel pump is 4 3/4 inches overall, 4 1/8 inches for the main body (black part in the photo), 1 1/2 inches in diameter, 6 inches from fitting to fitting. A white wire comes from the pump in the back and goes to the top. A black wire comes from the pump in the back and goes to the bottom. Photo below (for some reason it uploaded upside down). The copper colored device in the fuel cooler and the black body is the fuel pump. I still need to replace the fuel filter/water separator.

 

[alldodge]

The old pump number was 807949A1 and has been superseded by 861156A1. Here is your parts list for the cool fuel assembly
http://www.mercruiserparts.com/bam/subassembly/31880/2338/90

 

[Pete104]

Personally I have never experienced a noisy factory (Mercury) fuel pump. Volvo, yes.
The link AllDodge says alot but click the link of the part number. That will take you to a page that refers to Merc service bulletin # 2004-05. Google it. It comes up on pdf from mercruiserparts.com but I can't locate it on the sight.

My theory is that somebody has changed this fuel with whatever they could get their hands on even if ain't right.

 

[alldodge]

The issue with the bulletin is Merc wants the entire cooler replaced when the pump is replaced. The kit came with a new cooler which had a drain in it, the original did not have a drain. You can still find the part ending in 1 or 01 and the new part ends on 03 (861156A03) can use 01, 02 or 03

 

[DuncanDonut]

Terrific input. Thanks for your insight, folks. It looked as if the fuel cooler/pump package had been removed once before. I don't know how they did it without removing the alternator which looked like it had never been removed (still had paint on the bolt heads. At any rate, I think I know what to order if/when I decide to pay someone to make the switch. For the time being, I will take short trips and see if anything changes. I will replace the fuel filter in the water separator and I am also treating the fuel on the outside chance that there is some gum left over from previous fuel neglect.