Mercruiser 5.7 EFI Fuel pump noise normal? With video.

[96lt4c4]

I bought a 1997 Maxum 2100 SR2 about a month ago. The boat is very nice but has an issue when cruising above 3500 RPM. The boat starts to backfire through the TBI unit. I pulled the distributor cap and found lots of corrosion, I could tell it was original, so I replace the cap, button, ignition module and the spark plugs. While testing the boat in the driveway, everything seems fine. The boat starts good and revs good. I took it out on the water and it is still backfiring. Tonight I completely took the fuel system apart and looked for any blockage or bad gas. Could not find anything wrong. So I made up a rig to check fuel pressure and jumpered the fuel pump relay to run the pump constant without the engine running. The fuel pump is very noisy, I noticed this before but with the engine running it kind of masks the sound. I am showing about 30 pounds on the gauge but it fluctuates with the noise.

The fuel filter/water separator is new, installed it tonight. Filled it with fresh gas to prime the system.

I also removed the anti siphon valve and tried sucking some gas up out of the tank to see if I could feel any resistance. I felt none, and almost got a mouth full of gas...LOL. This was done before the last water test and didn't help anything.

This motor also has the cool fuel setup.

 

[96lt4c4]

https://www.youtube.com/watch?v=AoPHY2pv77o

 

[MikDee]

It sounds like your fuel pump is starving for fuel?

 

[Fun Times]

Sounds like you may have some air in the fuel system.

Try testing with an auxiliary fuel tank with an outboard fuel primer bulb so you can put additional pressure on the fuel system to see if it helps at all.


You may need to do a vacuum test on the fuel system. http://forums.iboats.com/forum/engi...ow-to-testing-your-boats-fuel-system?t=283269


Here's some fuel pump info for you catch up on if interested.
http://www.marinemechanic.com/merc/d...umptesting.PDF .................http://www.boatfix.com/merc/Bullet/00/00_05.pdf

........http://www.boatfix.com/merc/Bullet/02/02_03.pdf

Also you may want to follow this topic as well.
http://forums.iboats.com/forum/engi.../7758108-2000-350-mag-mpi-fuel-pressure-issue

Good luck.

 

[96lt4c4]

Thanks for all the replies, I am going to do some more troubleshooting tonight. I have some clear hose that I can install between the tank and the fuel filter. I may run to WalMart and get a bulb primer for an outboard and run that down into a 5 gallon gas can to see if I can force the fuel into the filter. That should clear up the fuel pump cavitation, if that is what is going on.

I am also going to install a ball valve between the return of the pump and the fuel filter. That should give me around 60 pounds of fuel pressure if the pump is in good shape. I saw this in the Mercruiser Manual #17.

All of my fittings between the tank and filter are tight, if I have an air leak in the the tank pickup, how do you get that out? I have tried tightening/loosening the pickup 90 elbow and the locking nut on top of the tank, they are very tight so I left them alone. This boat also has a Navman Fuel 3100 installed with a fuel meter transducer installed between the filter and tank. I can blow through it so it is not clogged. These ever cause problems?

Here is another video I made last night that I just got a chance to upload today.

https://www.youtube.com/watch?v=OzthyH0RXrw

 

[thumpar]

That is definitely not normal. I have the same motor. It should just be a gentle hum. Check the lines and try an external tank to the fuel inlet like Fun Times posted. It does sound like air in the line.

 

[96lt4c4]

Ok so I did some testing tonight.

First I removed the fuel filter and installed a valve on the the return side. Then I ran clear hose down into a 5 gallon can of gas with a primer bulb installed in the line. I primed the system and started the pump. Same noise. So I began to pump the bulb and the pump calmed down, the pressure went up a hair and stabilized. Since the external tank of gas didn't change anything I started taking the pickup out of the tank in the boat. I got it out no problem, the screen on the bottom was clean and I could blow through the tube. I pulled the screen off and capped the end off with my finger then sucked on the fuel fitting end. No leaks. I put it back together this time connecting the bulb to the tank in the boat. Same thing, if I pump the bulb up the pump calms down. With the pump running smooth I closed the valve on the return side and the pressure shot up to right at 60 pounds, so the pump is capable of building pressure.

I also took the fuel filter assembly off and pipe doped all the fittings.

I pulled the boat out into the drive and fired her up, pretty much the same thing, pump makes noise, prime the bulb, the pump calms down for 20 seconds or so. I also can not see any air coming out of the tank at all. I made another video.

It seems to me that if the pump is getting air I would have some type of a gas leak and I do not.

https://www.youtube.com/watch?v=JQNvb2-HYJA&feature=youtu.be

 

[Fun Times]

Have you ever noticed any debris in your fuel system or filter in the past? You may have a small blockage in the fuel line between the fuel filter base and the fuel pump hose or fitting at the pump. Or you may have a kinked hose between the filter base and pump or the hose may be blistered/disintegrating on the inside interrupting the fuel flow. It wouldn't be the first time that hose is compromised on the inside or out. Be sure you don't have two o'rings on the fuel filter/filter base.

If you can't locate a problem causing the noise it very well could just be an internal problem with the fuel pump itself. Since it's giving you the pressure you need, and you are trying to avoid spending big money on a "guess" of a bad fuel pump. You could try lubing the pump by either using the mixture stated in the service bulletin below for a "locked up pump" or many of the old time high performance racers will add a mixture of marvel mystery oil to help quiet down and cool the fuel pump.


http://www.google.com/url?sa=t&rct=...wfqXnxSvSNPQhSYRuTVOavA&bvm=bv.69411363,d.cGU

http://www.jamestowndistributors.com/userportal/show_product.do?pid=545 <<< If the link has a bunch of *** in it, you will have to add (james town distributors. com) to it or Google search marvel mystery oil ratio. Keep us updated , good luck.

 

[96lt4c4]

Have you ever noticed any debris in your fuel system or filter in the past? You may have a small blockage in the fuel line between the fuel filter base and the fuel pump hose or fitting at the pump. Or you may have a kinked hose between the filter base and pump or the hose may be blistered/disintegrating on the inside interrupting the fuel flow. It wouldn't be the first time that hose is compromised on the inside or out. Be sure you don't have two o'rings on the fuel filter/filter base.

If you can't locate a problem causing the noise it very well could just be an internal problem with the fuel pump itself. Since it's giving you the pressure you need, and you are trying to avoid spending big money on a "guess" of a bad fuel pump. You could try lubing the pump by either using the mixture stated in the service bulletin below for a "locked up pump" or many of the old time high performance racers will add a mixture of marvel mystery oil to help quiet down and cool the fuel pump.


http://www.google.com/url?sa=t&rct=...wfqXnxSvSNPQhSYRuTVOavA&bvm=bv.69411363,d.cGU

http://www.**************************/userportal/show_product.do?pid=545 <<< If the link has a bunch of *** in it, you will have to add (james town distributors. com) to it or Google search marvel mystery oil ratio. Keep us updated , good luck.

Thanks for the reply, the boat is new to me.
I took the whole system apart a couple days ago. I took the whole cool fuel system off the boat and inspected all the lines and the pump. The lines are clear and the screen in the suction side of the pump was also clear. The brass fuel log is clear. I took the regulator off the log and the screen under it was clear. I could not find signs of anything wrong. Filter is also new.

Beginning to think that I just need to replace the pump.

 

[96lt4c4]

Just ordered a new fuel pump. We shall see what happens.

 

[DANBRAUD]

I've been following your thread and was interested how is it going. I am having the same issue with my 2000 Mercruiser 5.7. I too have ordered a new fuel pump and fuel pressure regulator. Please keep us informed of your progress.

 

[96lt4c4]

So I got the fuel pump in yesterday and it did not fix the problem. Same symptoms. I took the entire fuel system off the boat. TBI, Cool Fuel unit, and the fuel filter. I assembled the whole thing on my work bench and stuck the suction side of the fuel filter down into a fresh tank of gas, with the bulb installed. I connected the fuel pump to a battery. Same issues. I am able to pump the bulb and prime the pump. The pump holds pressure when shut off, so to me that means the pump and regulator are working. I can put vacuum on the regulator while the pump is running and make the fuel pressure drop to 20 pounds.

So the next thing I did was bypass the fuel filter. I put the suction side of the pump directly into the gas can, as well as the return coming off the regulator. Pump runs good, holds 32 psi and does not make weird sounds anymore. Put the fuel filter back in the loop and it comes back. I have redone all the fittings on the fuel filter housing and inspected it till I am blue in the face and can not find anything wrong with it. I have pulled vacuum on each individual hose and they seem to hold. I am really at a lose right now. I hate to through money at parts I don't need, but I don't know what else to do.

DANBRAUD what are your symptoms. I didn't change the regulator so I would like to know what yours does.

 

[dubs283]

Put the fuel filter back in the loop and it comes back.

what brand water separating fuel filter are you using ??

 

[96lt4c4]

I cant remember off the top of my head, Bought it at a local marine shop and it was a replacement for the Mercury part number that was on the old filter. It was also about an inch longer. The issue was there with the Mercury filter too. The previous owner told me he changed it last year, but I changed it again anyway. Same issue. The gas has eaten the paint off the new filter.

I just found a picture of it online...this is it.

Fuel Filter Water Separator Marpac 7-0860 Canister Only Mercury 35-60494-1

http://www.ebay.com/itm/like/161100149403?lpid=82

 

[Tail_Gunner]

Do something simple here take off the fuel line to the TB...attach a hose to the line and turn on the key and watch the stream..just make sure you have a safe place for the fuel to go and a fire extinguisher..id run a gallon or two to one see if it will purge and two find the vacum problem.....have you checked the voltage to the pump and see if it's constant

 

[96lt4c4]

Do something simple here take off the fuel line to the TB...attach a hose to the line and turn on the key and watch the stream..just make sure you have a safe place for the fuel to go and a fire extinguisher..id run a gallon or two to one see if it will purge and two find the vacum problem.....have you checked the voltage to the pump and see if it's constant

Ok, I will try that. No I have not checked voltage, but I am running the pump on an external battery right now, out of the boat.

 

[dubs283]

Mercury 35-60494-1

the proper number from mercury is 35-802893Q01 for a water separating fuel filter [h=1][/h]

 

[96lt4c4]

the proper number from mercury is 35-802893Q01 for a water separating fuel filter

This filter replaces Seachoice 20911, Valmar 52113, Sierra 7844, Racor PFF 5510, Moeller 03332410, Mercury 35-802893Q01, Marpac 7-0860

 

[96lt4c4]

Ok, I am about ready to give up and scrap the whole cool fuel system an make up my own custom fuel system with an aftermarket fuel pump, adjustable fuel pressure regulator and stainless braided fuel lines....I made this video last night. Anymore ideas would be appreciated.

https://www.youtube.com/watch?v=YEVnBp7-Lu0

 

[Moonstruck]

I have pulled vacuum on each individual hose and they seem to hold. I am really at a lose right now. I hate to through money at parts I don't need, but I don't know what else to do.

Since the system is apart and on the bench, have you tried plugging the lines and putting pressure on them? See if that holds. Test the fuel filter mount also. Have you inspected the fuel filter mating surface for scratches or damage that may cause an air leak? It sounds like a parasitic air leak somewhere. Isolate and test each part.