Help identifying sound on 98 Mercruiser 350 Mag

[woodman4 1]

Hey guys, long time forum lurker here needing some help with my new (to me) boat. It runs great but has a “whining” sound that I can’t figure out. It only makes the noise while engine is running (not when key is “on”) and doesn’t seem to be effected by rpm. The only thing I have noticed is it getting higher pitched as the battery voltage climbs after starting up. I thought it might be the alternator so I swapped it out but that didn’t change anything. Anyone have any ideas? I have short video on YouTube and will include the link. Thanks!

 

 

[Shaka 146]

I'd check the pulleys and belt.

[Jake707 171]

It sounds the same as my 98 Tahoe 350 and it was the belt tensioner. Try running it and with a squirt bottle try wetting just the belt while spinning and see if it helps any. I would start at the belt, idler /tensioner pulley

[woodman4 1]

Thanks for the suggestions. Going to check it out this afternoon if I have time. Hope it’s something simple like a pulley.

[woodman4 1]

Pulled the belt off and removed the tension pulley and I believe that is my problem. I can shake it in my hand and hear the bearings rattling around. Looks like it and the idler pulley are the same part so I will probably just replace both of them while I’m at it. Anyone know if this is a part I can just take to an auto parts store and get a replacement? Not sure if there is anything “marine” specific about it, and when I look it up online I have several different pulleys come up. Bearing part number is 6203LH and pulley says Dayco 00076.

[Jake707 171]

I would take it to the auto parts store closest tell them you have a 98 chevy Tahoe with the 5.7 and compare the pulleys they pull off the shelf to yours. I would think they are the exact same.  They will probably ask if its 4x4, or AC, or what color blah blah haha  like any of that matters for the part Im looking at.............. but that's what you get when theres a 16 year old behind the counter starring at a computer screen.

[woodman4 1]

3 hours ago, Jake707 said:

I would take it to the auto parts store closest tell them you have a 98 chevy Tahoe with the 5.7 and compare the pulleys they pull off the shelf to yours. I would think they are the exact same.  They will probably ask if its 4x4, or AC, or what color blah blah haha  like any of that matters for the part Im looking at.............. but that's what you get when theres a 16 year old behind the counter starring at a computer screen.

You just described exactly how it went at the parts store today lol. I did end up finding the right pulley eventually. However, the pulley isn’t the issue. Put it back on and started it up, same noise. I do still think that pulley/bearing was on its way out though so I’m not mad about it. 

One thing I did notice this time around was that the fuel pump does actually make a similar sound to what I’m hearing when I turn the key on and the pump primes. It’s lower pitched than when it’s running but I guess that would make sense as the voltage climbs it would get louder/higher pitched. I didn’t notice it making this sound before or I probably would have started there. 

So now I’m on to the fuel pump. Anyone ever replaced their own? Looks like they’re about $200 online. I’ve been looking for a write up or video on it but haven’t come across anything yet. If anyone knows where I can find some kind of instructions that would be great. 

[Jake707 171]

I havent experienced a noisy fuel pump before. I havent replaced one in my boat is it external or a drop in unit in the gas tank? Both are pretty straight forward replacing however access I think is going to be the biggest hurdle. If its an internal unit theres an access port center of the floor more forward by the captains chair that should allow access to the top of the tank. once there take a flat head screw driver and hammer, knock the locking tab counter clockwise until its unscrewed, unplug the top connector then the whole assembly will come out ( you would need to pull straight up a couple inches then at an angle to clear assembly, just go slow and be gentle until you understand its shape. Then reverse with the new unit.

If its an external pump just follow fuel line back from carb or fuel rail if FI until you find the cylinder shaped pump. Disconnect electrical connectors, supply lines one each side and replace.

Also just to check your other pulleys run it and spray a small amount of WD-40 on each pulley, one at a time, and see if it goes away

[woodman4 1]

This is the external pump the sits way down low on the starboard side, in the same box as the cool fuel unit. I had my wife cycle the key in and off so I could listen to it. I got another one for 100 bucks that I’ll hopefully be able to throw on there tomorrow. It does look like a pain to get to but I’m hoping it won’t be as bad as it looks. 

[Jake707 171]

If you can fit one, put a towel under the unit so the gas that leaks out is absorbed and then take it out and let if air out for awhile once the new pump is in before starting. Otherwise you might get a nice boom in there from all the fumes.

[Nick213 583]

Good point jake. I was just gonna say start by lighting a cigarette then go about removing your fuel lines ?

@woodman4 on a serious note do you think it might be a vacuum leak? I had a Toyota back in the day that made a similar noise and it was a vacuum leak.

[woodman4 1]

I really don’t know about a vacuum leak, never had to deal with anything like that before. I really feel like it’s the fuel pump. 99% sure it’s electrical because of the way the noise pitch changes as the voltage gauge climbs. I got my head in there as far as I could while it was running and the sound is definitely coming from down low on the engine and on the starboard side. If this fuel pump doesn’t fix it I’ll start looking at how to diagnose a vacuum leak. Thanks for the suggestion.

[woodman4 1]

4 hours ago, Jake707 said:

If you can fit one, put a towel under the unit so the gas that leaks out is absorbed and then take it out and let if air out for awhile once the new pump is in before starting. Otherwise you might get a nice boom in there from all the fumes.

Good suggestion, I’ll do that for sure

[woodman4 1]

Fuel pump has been removed and new one will be here tomorrow. So far it hasn’t been too bad. Removed the alternator to give me a little more space. Opened up the cool fuel housing, removed one bracket and the whole cool fuel/fuel pump assembly slides far enough out of the plastic box to disconnect it from the fuel cooler. Unhooked the wiring and then was able to pull the pump all the way out to the port side locker to get a wrench on it.

Only thing I’m not sure about is the two o-rings that are on the current pump. They look a little worn and I don’t think the new pump comes with any. Going to go to the parts store tomorrow and hope they have a kit with some replacements in it.

[woodman4 1]

New pump showed up today and one of the wires was cut in half. I was going to put it back together but I have to wait on the o rings I ordered to come in so I am just getting a replacement pump. Hopefully I’ll have it all back together by Thursday.

[Jake707 171]

Keep us posted but timing wise it sounds like its all coming together with the o rings and new pump delivering about the same time.

[woodman4 1]

Just got new pump installed and this issue has been fixed. Thanks everyone for the help.

 

Only thing I’m having a problem with now is getting the bracket bolted back on the the fuel pump/cooler. The bracket also acts as a heat sink to remove heat from the fuel. It is secured with 2 nuts that thread on to some “studs”, which are somehow connected to the cool fuel housing. When I try to tighten down the bracket, the stud closest to the front pulls out of the hole that it sits in. I’ll work on that some more tomorrow and hopefully have this thing back 100%. I took a picture but it’s too big to upload. 

[InfinitySurf 302]

1 hour ago, woodman4 said:

Just got new pump installed and this issue has been fixed. Thanks everyone for the help.

 

Only thing I’m having a problem with now is getting the bracket bolted back on the the fuel pump/cooler. The bracket also acts as a heat sink to remove heat from the fuel. It is secured with 2 nuts that thread on to some “studs”, which are somehow connected to the cool fuel housing. When I try to tighten down the bracket, the stud closest to the front pulls out of the hole that it sits in. I’ll work on that some more tomorrow and hopefully have this thing back 100%. I took a picture but it’s too big to upload. 

You can resize pics to post by using this link...its how I post pics.

http://www.resizeimage.net/

[woodman4 1]

I was thinking about that stud last night and I’m starting to think that it was glued in to that hole from the start. When it came out I noticed it had a bunch of grime/corrosion on it that I cleaned off, but now I’m thinking that was the adhesive they used at the manufacturer. I’m thinking I’ll just put some jb weld on it or some other kind of high temp adhesive and that should work.

[woodman4 1]

Here’s the only picture I could get. Not easy to get a phone camera down in there. The stud on the right it the one that keeps coming out.