Jump to content

Welcome to TheMalibuCrew!

As a guest, you are welcome to poke around and view the majority of the content that we have to offer, but in order to post, search, contact members, and get full use out of the website you will need to Register for an Account. It's free and it's easy, so don't hesitate to join the TheMalibuCrew Family today!

Tracking down a noise in the engine compartment


Recommended Posts

Please help me solve a puzzle...

We noticed a weird noise at Lake Oroville last month coming from the engine compartment. It only seemed to occur at low RPMs/speeds (5 - 7 MPH per the speedo). The boat is a 2000 SLXi with the 325 Monsoon II.

I'd characterize the noise as a kind of repeating squeak (eenh-eenh-eenh, etc.) like something was spinning without full lubrication. We noticed it when we were driving through the never-ending 5 MPH zone by the launch. The sound was distinctly noticeable at that speed but went away (or was masked) at higher speeds. It also did not occur if you were idling forward at a lower speed (basically put the boat in gear at minimum throttle).

I checked all fluids (again) and didn't find anything out of place. The oil and transmission fluids looked good.

I pulled the access panel behind the engine compartment and the noise did not appear to be coming from the shaft area.

I opened the clamshell and the sound seemed to come from the rear area (motor/transmission/shaft?). It did not appear to be coming from the belt area at the front.

We had not noticed the sound previously here in Bend, Oregon, and thought maybe it was related to the change in altitude (3500' vs. 300'). Also, we found that the sound wasn't always there running at low speed after running at high speed (25 - 30 MPH). We'd get it sometimes and not others on the run in to the house boats. After the motor sat for a while we'd typically get the noise on the run back out to the lake.

I checked this last week on the lake and was able to hear it at altitude, but it was much less pronounced. The other variable, though, is that we don't have to run at low speed for long distances.

Any thoughts on what to check?

Thanks,

Mike

Link to comment

I had that once, in my case, it was the fuel pump. My personal (not professional :)) opinion is that your may be on the fritz.

Next time you hear it, follow the fuel supply line and try to listen to the fuel pump (if facing the bow of your boat, the fuel pump is on the left rear of the engine and looks like a 6" cylinder with the fuel lines coming out of it). It will squeak (or if its gone, squeal) at slwo speeds, but as the pump goes faster, and more fuel is drawn through, it isn't as likely to make the sound with the higher flow rate.

Just a thought of something to check,

JZ

Link to comment

Thanks JZ...I'll check that out. Kind of makes sense and doesn't sound like anything too difficult to fix if that is the culprit.

Mike

Link to comment

Does anyone know if the "marinized" fuel pump is any different that the automotive fuel pump?

Just curious in case the fuel pump turns out to be the culprit whether I'll have to buy parts through the Malibu dealer or if I can go automotive on this part.

Thanks,

Mike

Link to comment

During my last trip I also noticed a similar noise at the speeds you described. I thought it was coming from under the hull and was also thinking cutlass bearing. Boat ran flawless and noise wasn't loud enough or consistent enough to warrant too much concern though. However, now that the fuel pump was mentioned I'll have that lurking in the back of my mind during next trip. :unsure:

Link to comment
Does anyone know if the "marinized" fuel pump is any different that the automotive fuel pump?

Just curious in case the fuel pump turns out to be the culprit whether I'll have to buy parts through the Malibu dealer or if I can go automotive on this part.

Thanks,

Mike

Mike an automotive pump is not acceptable for a replacement. You need to get the OEM from your dealer.

Link to comment
Does anyone know if the "marinized" fuel pump is any different that the automotive fuel pump?

Just curious in case the fuel pump turns out to be the culprit whether I'll have to buy parts through the Malibu dealer or if I can go automotive on this part.

Thanks,

Mike

Mike an automotive pump is not acceptable for a replacement. You need to get the OEM from your dealer.

Thanks...that's what I thought but it never hurts to check! :)

Link to comment
One other thing to consider is your cutlass bearing. 

what / where is a cutlass bearing ?

At first I thought it might be a joke like muffler bearings but it turns out that its the bearing between the shaft and the shaft strut. Here's a link to an article that describes the cutlass bearing.

Link to comment
One other thing to consider is your cutlass bearing.  I occasionally have the noise you describe in no wake zones, but just a slight touch of throttle makes it go away.

Guess I should be able to test that with my fake-a-lake. Take the engine out of gear and run the throttle at the low RPM range. A fuel pump problem should still occur but the cutlass bearing should not (as long as the transmission is truly disengaged and the prop isn't moving).

So the next question is, if it turns out to be the fuel pump and it only makes the noise at a narrow range of RPMs, how urgent is it to replace the pump? Is it causing damage to anything else? Will it continue to run like this and gradually get worse or am I at risk of a sudden failure?

Thanks again for all the help!

Link to comment

IF so many people are noticing this noise, it may not be the fuel pump and could definitelyl be the bearing. I definitely had a squealing fule pump in my case. It started out rare and slow and definitely blew up in a split second one day while I was running WOT. If you can trace it the fuel pump, I'd recommend replacing it as soon as you can and hanging on to the old one as a backup. Unfortunately they aren't cheap, but the replacement is a piece of cake.

JZ

Link to comment
CarveItUp Posted Today, 12:26 PM

  So the next question is, if it turns out to be the fuel pump and it only makes the noise at a narrow range of RPMs, how urgent is it to replace the pump? Is it causing damage to anything else? Will it continue to run like this and gradually get worse or am I at risk of a sudden failure?

I've had to replace 3 automotive fuel pumps over the years and all went out suddenly, without warning.

Your idea to test run it on the trailer sounds like it might work, although I have noticed my prop turn slightly when flushing the engine even with the tranny out of gear. ( The cutlass bearing really howls when it's dry! )

Link to comment

After rereading your post, my noise is exact. Not at in gear idle, but as soon as you give it some gas, its there and then gone as you gain speeed. The only other thing I noticed was some brass dust directly where the shaft packing drips.

Edited by Web
Link to comment

I had a squealing whistling sound on my lxi 325monsoon, that drove me nuts. Thought it was the fuel pump. Engine ran perfectly no problems but at low rpm..like a little bird in the engine compartment. You wont believe it but finally traced it to the small 1/8 inch hole in the butterfly under the flame arrestor. Just put ur finger over the hole and it'll disappear. Honest...

Link to comment
I had a squealing whistling sound on my lxi 325monsoon, that drove me nuts. Thought it was the fuel pump. Engine ran perfectly no problems but at low rpm..like a little bird in the engine compartment. You wont believe it but finally traced it to the small 1/8 inch hole in the butterfly under the flame arrestor. Just put ur finger over the hole and it'll disappear. Honest...

Wild...I'll check that one out too when I do my testing.

Thanks!

Link to comment

i just started picking up on a noise that may be similar on my 04 response lcr with 250 hours on it. i'm also thinking fuel pump.

noise sounds a lot like the modem chirping on the computer when you first attempt a dial-up connection. anyone second the noise description?

initial guess was a noisy fuel injector. pulled the power lead from each while at idle. the noise remained constant. i was impressed with how well the controller maintained idle as i played.

Link to comment

Did some troubleshooting in the driveway this evening. Increasing the throttle (out of gear) from 700 RPM to the 1000 - 1200 RPM range resulted in the noise starting up. Much higher than 1200 RPM or below 1000 RPM and the noise goes away.

It's definitely not the cutlass bearing because the drive shaft was not turning.

It's not belt noise because we lubricated the belt and lost the belt noise while this noise persisted.

Checked the butterfly valve on the throttle body and it is not the source of this noise.

Used a length of hose as a stethescope to check the fuel pump for noise. It does not appear to be coming from the fuel pump.

The noise seems to be coming from something at the center in the very back of the engine compartment. You can feel the vibration in the throttle arm but not hear it with the tube. Checked the fuel injectors and they sound normal. Checked the transmission housing and no noise at all (makes sense since it's out of gear).

At this point I am thinking it is some sort of vibration-based noise that is triggered in that RPM range. We don't think it's mechanical and all indications are that the engine is running fine.

I guess we'll keep trying to trace it down as time permits...

Thanks for all the suggestions! It feels good to be able to rule out some possibilities...

Link to comment

Have you checked the engine mounting bolts? The ones attaching the feet of the mounts to the stringers are known to have bolts with short thread length so they tighten but not enough to secure the mount. The inside nut is accessed through the black vent on the engine stringer and lots of contortion. If you find them loose and tighten them, be sure to check you engine alignment. The distributor can become pretty corroded in side and possibly cause a noise, but not likely a vibration. More likely would be the transmission flexplate out of balance or deteriorating. I'd check for vibration with a metal stethescope touching different parts (non-moving) if you reproduce the sound/vibration at a given rpm.

Link to comment

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Restore formatting

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...