Sucking sound from 500 EFI ???
 

Okay, I really am counting on you guys for the answer.

I have a 2002 Merc 500 EFI that runs great, all is well according to the scan tool, oil temp and pressure are perfect, all injectors check out fine and a compression check showed all is well.

However there is a very big sucking sound coming from this motor.

I have replaced the Map Air Sensor, Intake air temp sensor and the IAC motor. Actually have just tried another IAC motor. I took the throttle body off if that is the right description, the part with the butterflies that the air filter hooks to and doubled checked the o-ring gasket between it and the plenum and all was well.

This is my port engine, and the starboard engine does not do this. Funny thing, but my best friend has 500EFI's also and he is having the EXACT same problem with the same engine. We have both messed with this for a month now and cannot locate the problem.

I had a buddy to tell me that he actually thought it was a bearing noise from the alternator instead of a sucking sound, so I ran the engine without the belt and it is not coming from an accessory. Very clearly an air type sucking sound.

Does anyone know where or what we need to be looking at to find the source of this problem.

Your help is much appreciated

Dock Holiday & Steel Outlawed

Re: Sucking sound from 500 EFI ???
 

Dock,
have u tried an auto stethescope on bearing areas, ie. alt, ps pump,
Or if you really think it is a sucking noise, I would try a can of berryman's carb cleaner. simply spray carb cleaner with the pinpoint nozzle in the vicinity (around injectors) of the noise a little at a time while keeping a close eye on your engine rpm. if RMP raises in that area where your squirting, then track down to see if there is a hole in a gasket or ripped airhorn bringing in unmetered air. Keep the fumes away from the intake as it may give you false rpm increases.

Oh, if you try this technique, you may want to have a fire extin handy.

worth a try and good luck,
gociggie

Re: Sucking sound from 500 EFI ???
 

Where do you live? What weather conditions are you running the motor in?

Re: Sucking sound from 500 EFI ???
 

that noise is the money leaving your wallet everytime you start it up.

Re: Sucking sound from 500 EFI ???
 

PCV valve hose ???

http://www.mercruiserparts.com/Show_...And+Components

item # 9

Re: Sucking sound from 500 EFI ???
 

Probably more air going past IAC valve than normal. This makes a big sucking sound, just like you describe. If there is some carbon around throttle blades or throttle blades are set more closed than normal, the IAC will open further and thus more air going thru idle speed passage and thus more 'sucking' noise.

Also, adding a different flame arrestor can make this noise more pronounced.

Lastly, if you are not used to listening to your motors with the hatch up and you are doing so now (where they are normally closed) you will here a ton more noise.

Re: Sucking sound from 500 EFI ???
 

That's a good idea with the carb cleaner. Would starting fluid do the same thing?

Yeah that's me, I'm the friend with the same problem. It is getting very annoying

Re: Sucking sound from 500 EFI ???
 

What does the scan tool say the IAC position (at idle) is on that engine compared to the other engine?

If it' s high, then there may be a performance issue that is forcing the ECM to open the IAC a lot to maintain the desired idle speed. If it's low there may be a vacuum leak.

Dave

Re: Sucking sound from 500 EFI ???
 

North Carolina

70 to 90 degree temps, high humidity.

Re: Sucking sound from 500 EFI ???
 

SB,

I did have carbon build up around the throttle blades and cleaned all of that off. I compared the opening to that of the other engine and they are the same. Also played with that adjustment a little and saw no difference. Both engines are idling at the same RPM.

I do have after market flame arresters on the boat, but they have been on it for three years now. Again, the Port engine is as quiet as can be. I have heard they type of noise before when I had a bad intake valve on an engine, but this engine runs great and the compression test is perfect.

I'm going to look closer at the IAC and compare the reading to the other engine, then look at the o-rings around the injectors.

Thanks for all your help.

Dock

Re: Sucking sound from 500 EFI ???
 

Dave,

I'll check that this weekend. Where would you start at looking for a vacuum leak?

Thanks
Dock

Re: Sucking sound from 500 EFI ???
 

I'll take a close look at that also.

Thanks

Re: Sucking sound from 500 EFI ???
 

switch arrestors between the motors. There is a small filter intake inside the plenium that will get carboned up also. I had a 525 last year that was making a whistle noise and it turned out to be the intake gasket. I changed the iac and all gaskets before finding it.

Re: Sucking sound from 500 EFI ???
 

I have a pair of 500 EFIs' in my current boat and I also hear a rather loud air"sucking" sound at idle, sometimes, especially upon cold start up, or when backing off from higher RPMs. My previous boat with a single 500 EFI did it also, especially if you would rev the engine and back it off quickly - was told it was the IAC system. Engine also sounded really loud when it was cold, ie, just started for the first time that day. The sound would gradually go away once the engine started to warm up. I now live in North Carolina, previously in Ohio, and have noticed that down here in NC, that the IAC system seems to work harder/longer than when I lived up north (if that makes any sense). Having 2 of them side by side, now, makes the intensity of the noise even more noticable, but it does gradually quiet down as the engines warm up, or if you blip the throttle, it will kick in until the idle speed goes back down to 750ish.

Re: Sucking sound from 500 EFI ???
 

\



Never tired starting fluid, but should work, just make sure you have a pin point nozzle to direct your spray otherwise the intake will take over and defeat your efforts.

be cautious around hot exhaust, tends to ignite.

Re: Sucking sound from 500 EFI ???
 

:stupid:

Re: Sucking sound from 500 EFI ???
 

There are several reasons to NEVER use "starting fluid" in situations like that. DEATH is the biggest one. Fire is second and engine damage is third. The fumes from a can of ether can become so dense in the engine compartment that you will pass out, fall in and possibly die. The fumes can be easily ignited by a bad spark plug, wire, dist. cap etc and you burn or die. The boat can burn. If you find a big enough vacum leak with ether, you could blow a piston apart.

A nice, safe way is to use a (non flammable) brake cleaner to do the same job. The exhaust will start to smoke and smell like hell if you pull brake cleaner thru the combustion chamber. Its non greasy, doesn't leave a mess and wont blow your arse up.

Re: Sucking sound from 500 EFI ???
 

for 25yrs been using carb cleaner to find vacum leaks, start mtrs, and diagnos fuel problems

its a little less combustable then ether and works great

Re: Sucking sound from 500 EFI ???
 

I had that same problem--in the end it turned out to be failure of fuel pressure regulator. We changed everything and just happend to look at pressure regulator and it had corroded under paint and jammed partially open. As soon as we changed that unit the problem was solved.

The corrosion wasn't visible---found it by scrapping paint to find the part number and the things was all bubbled up. Was a good thing we found it when we did--if it had let go would have been some explosion.

Re: Sucking sound from 500 EFI ???
 

Use WD-40...It wonk strip the paint or burn your boat down....It will pick-up the RPMs....

BOB-T !!....Where ya been ???....Whatcha got now ? :D

Re: Sucking sound from 500 EFI ???
 

Birdog, we're still in Raleigh, NC. Sold the 29 (to someone just outside of Cinci, of all places!). Just bought a 35 Lightning Twin Step with a pair of 500 EFIs', sitting on a Myco trailer! Boat only has 115 hrs on it and is like new! Vacu-flush head, refrigerator, fresh water system, bimini, cabin, never used! I'll send you a couple of pictures, when I get some. Do you have your TG up and running? Didn't set anything up for the Lake Cumberland Poker Run this year - too much hassle doing it "remote" from NC. I'll give you a call! :D

Re: Sucking sound from 500 EFI ???
 

Okay, I found the problem!!!!! :D

First want to thank all of you again that took time to respond and offer help. It is very much appreciated. That is what makes this site great.

I put a new IAC motor on, because that was the only thing that had been touched on this motor. It was fine before. Then I noticed a little corrosion around the thermostat housing and desided to pull it and put a new one in and new gaskets.

This gave me the perfect opportunity to pull the plenum off and PRESTO.

What did I find, but two broken o-ring gaskets between the Plenum and the intake runners. They had both split and had a 1/4 to 3/8 inch gap.

Problem solved!!!!!!!!!!!!!

You will need 8pcs. of the Mercury 25-805732 O-rings for the repair.

I will probably do this to the other engine over the winter. Mine are 2002 models and it was time I guess.

Hope this will help some of you guys out that have been sending me PM's with the same problem.

Good luck and thank you all.

Dock

Re: Sucking sound from 500 EFI ???
 

Good job! Did you check the IAC position, and was it low? Just curious.

Dave

Re: Sucking sound from 500 EFI ???
 

Nice Dock! :cool: Has Steel Outlawed checked his??! :evilb:

Re: Sucking sound from 500 EFI ???
 

I called him last night as soon as I found the problem. He is leaving for a poker run tomorrow, so I guess he will not worry with it till he returns.

Re: Sucking sound from 500 EFI ???
 

No, I have not done that yet. I'll be on the water tomorrow and will hook the scan tool up and see what we have.

Re: Sucking sound from 500 EFI ???
 

glad to hear you found the problem, best of luck for the rest of the season !!!!!

Re: Sucking sound from 500 EFI ???
 

Just something else to think about here, when the IAC motor opens it causeing a sucking noise (we know that). When the engine is cold it is open , as the engine warms up, it should close ( we also know that ). When I put the Arizona Speed and Marine larger thoddle body on it was whisling very loud. Spoke to AS&M and they advise me to get the engine to running temp (140 150) and adjust the butterfly open untill the whistling stops. That way the engine is getting enough air that the IAC motor doesn't need to open, and therefore eliminate the whistling sound. I did this and has been fine even sice. I really didn't have to open the valve very much. I only here it now when the engine is cold.

Just FYI...

Hey how hard is it to pull the plenum off? I am having the same sucking noise. If I pull the plenum off do I have to replace the gaskets if I find that they are not bad? Also does anyone know what the torque specs are for the plenum bolts, and is there a certain pattern to follow when you tighten the bolts? Thanks, Mike

It's very easy to pull the plenum. Remove the throttle body, unplug all the sensors, remove the throttle cable, and all the bolts and it pull right off. The gaskets are o-rings so if they are good no you do not have to replace them. I don't know the correct spec for torque, but I just got them tight in a cross pattern while tightening.

Dock, did you wax the intake while you had the plenum off?

Well I'm glad to see this thread still here and still helping folks.

Actually if you have a reall good hydraulic shop in the area you can go and buy the o-rings for about .35 cents each. That is what I did once I found the right size and I keep a spare set in my shop.

Like Jeff said it is easy, you really cannot mess up and all they are is o-rings and not gaskets. Personally I would replace them all if it were me and I had it apart.

Good luck

Great post, I've learned a lot since I'm having the same issue on my 500efi, I'm also having surge issues, sounds like a 1071, can't imagine these issues are related,or are they?

Swap the 2 IACS...Heck, swap the throttle bodies complete.

Seems to me I had the same issue a few years ago so I'm a little fuzzy on the details, but I think I found I had low vacuum at idle & a large vacuum leak. The sucking sound may be air getting sucked past an almost completely closed IAC.