7.4L combo sea water/fuel pump maintenance

I have been following your post with great interest as I really hate these combination pumps on my boat. One question I have is how did you handle the plumbing from the new electric pump to the carb? I assume you removed the existing stainless steel tubing that ran from the mechanical pump to the carb and replaced it with a hose fitting on the carb and ran a hose from your electric pump right to the carb? I was also considering doing away with the entire remaining water pump housing and switching to Jabsco's brass Mercruiser replacement to do away with the plastic pump housing.
 
J Levine said:
I have been following your post with great interest as I really hate these combination pumps on my boat. One question I have is how did you handle the plumbing from the new electric pump to the carb? I assume you removed the existing stainless steel tubing that ran from the mechanical pump to the carb and replaced it with a hose fitting on the carb and ran a hose from your electric pump right to the carb? I was also considering doing away with the entire remaining water pump housing and switching to Jabsco's brass Mercruiser replacement to do away with the plastic pump housing.

Great question....I should have taken a picture of that as well. When I get back from travel, I will add a picture of the safety switch and the fuel line during the weekend.

Basically, the fuel line (pressure side) from the electric pump runs to the spin-on fuel filter. From there, I bent a new stainless line to the carb. You could accomplish the same thing with marine grade rubber fuel line and hose barb. The year after I installed the fuel pumps, I took it a step further and tossed the Mercruiser Carbs (and intakes) and replaced them with Holley Marine 800 cfm carbs and stainless braided fuel hose with AN fittings. I hated the way the old carbs leaked down and 10+ years on a carb is a lot. Now it starts like fuel injection, no more pumping and they are much more responsive.

I like your idea of Jabsco units. They are far superior to those plastic combination units. That is the right solution.
 
This is the safety switch for the Fuel Pump. It attaches at the end of the brass tee. The original pressure switch is attached on the right angle of the brass tee (you can make out part of it to the left of the safety switch).
 
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These pictures show the routing of the fuel line at the front of the engine. I hope they help.

-John
 
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Thank you for the pics! Looks like a very nice setup now! I'll have to get under the tarp this weekend and take a look at my setup.

.......Joe
 
In the picture below the cam that you are referring to, the cam is show. Currently with the pump off and the belt still on, the cam spins freely with a flick of my finger. Is this supposed to be like this or is it only to spin when the whole cam shaft is spinning (driven by the belt). The reason for my question is that my carb was not receiving fuel and when I went to replace the fuel pump I noticed this cam would spin freely. Is there a clutch system built in that freezes the cam in position in order to drive the fuel pump or has the cam broken away from the shaft? If so can it be replaced or do you have to replace the whole pump unit?
Now on to the fuel pump part. Remove two bolts, and the fuel pump is removed from the housing. You will need a new fuel pump gasket when you do this. The fuel pump itself is pretty standard, as you can see in this picture of it removed.

fuel_pump_off.jpg


Sticking out the right side of the fuel pump in the upper left is the arm that moves to pump fuel. It rides on a lobed cam on the pump shaft. You can see this cam in the housing in the main unit in the photo.

Here is where the issues begin. First, there is the possibility that there will be a little fuel leak past the gasket in the fuel pump, and it will get into the housing. In a normal engine, this would just go into the multiple quarts of engine oil, and be dumped in the next oil change. And never be noticed.

So second issue is that this reservoir is very small compared to the quarts of oil in an engine block, so dilution of the oil with gasoline will occur much more quickly if there is any or movement of fuel through the gaskets at all.

Third issue is that I think the normal maintenance does not call for replacing this oil, it only calls for removing the plug and topping it off. I could be wrong about this part.

Fourth issue, if oil gets diluted, then you are more likely to get wear of the arm and the cam. So you will start to get metal contamination of the oil. Again, it is only a small amount of oil, and there is no pumping and filtering to get rid of it. So it will try and settle to the bottom,where the shaft bearings are! :smt013

Fifth issue, if the oil gets diluted significantly with gas, it is more likely to leak by the bearing seals and get out, taking the oil with it.

So when you take it apart, look at the fuel pump arm, and check for wear. Here is what mine looked like, which appears OK to me.

fuel_pump.jpg


Look down at the pump cam, it should also be nice and smooth, and not show signs of wear.

In the picture below the cam that you are referring to, the cam i

pump_cam.jpg
I

Lastly, here is a photo looking down inside the pump housing, past the cam, and into the end of the housing where you can barely see the bearings. This is where you really don't want any worn metal particles to remain.

fuel_pump_bearing.jpg


So what you really need to do, with this thing taken apart, is to flush out the old oil (and maybe gas), get out any contamination, and refill it with fresh oil.

If you take care of it, knowing the issues, it should take care of you. If you don't, well, you could just be caught with a non-working fuel pump and sea water pump.

If I remember right, on mine, the first indication of a problem was of a small amount of leaking from the front seal where the pulley is, and I could not decide if it was oil or gas. So now I think it was both. After a flushing and oil change, it now has no leak that I can detect.
 
Here you go... The last picture gives you a view of where they are placed in relation to the fuel valves. I forgot to shoot a picture of the safety switch but it is very easy to install. The existing oil switch is located on the right rear of the engine block as you face the engine. Just remove the factory switch, insert a 1/8 npt tee fitting, install the factory switch on the right angle of the tee and the safety switch on the straight part of the tee. The wiring of the safety switch is important since it shuts down the fuel pump if oil pressure drops below 5 psi.

One more thing. You will notice a vent hose leaving the port pump. This hose attaches to the same spot on the carb as the mechanical pump did. You can't see the hose on the starboard pump because it comes out behind the pump.

-John

Hi John, I know it's been about 10 years since you originally posted your elecetric fuel pump conversion information. I've got a '94 SeaRay Sundancer 270 with a single 7.4L Merc Gen V, and would like to do the same. For whatever reason I don't see the photos you posted way back in '07. Any chance you still have them?
 
I have no idea where they went..... that said, I'm headed down to the boat tomorrow and will shoot a few more and post them. The setup has worked great for 15 years and makes starting and impeller maintenance a lot easier.
 
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I shot these yesterday. The system has been in place for 15 years. You can see the Fuel Pump Block off plate, the Holley Red Pump and the Holley Fuel Rail and Carb. What you don't see is the Holley oil pressure safety switch.
IMG_2899.JPG
IMG_2900.JPG
IMG_2901.JPG
IMG_2902.JPG
 
I just noticed this is a thread that started 11 years ago!! Never mind.

I was just a victim of this exact issue. To make the short story long, I sent the boat for service, the engine was working fine. In my first trip after this service, the engine suddenly quit (I had to be rescued and brought back to the marina). Before this happened, I noticed that when underway I could hear a squeaky noise coming from the engine so once back at the marina I disassembled the complete part (your first picture at the beginning of this thread). Big surprise when I found no oil at all in the reservoir, and the arm of the fuel pump worn out. You can imagine the discussions with the marine yard (mechanic, shop manager, etc). They said they never touched that part, even though the sea water pump impeller was replaced. To this day I can not prove my theory (someone, by mistake or intentionally) changed this part from another boat). Another reason that supports my theory is that they showed me a completely worn out rubber impeller, I mean just the core of it, no vertical sections) and I never noticed any increase in engine temperature, always 170 deg F before I sent the boat for this infamous service....
Interesting.....
 
I know this is an 11 year old thread but does anyone have the pictures from the original poster showing the combination fuel pump/sea water pump?
 
I know this is an 11 year old thread but does anyone have the pictures from the original poster showing the combination fuel pump/sea water pump?

I had these on my 1995 37 DA. If you see black sludge under the pump, time for a new one. Here's a picture of one. The water pump impeller is on the left and the pump in the middle (between the pump and pulley). The pump fits onto a lever arm that rides on one of the cam lobes.

upload_2019-6-15_9-22-18.jpeg
 
Thank you. I have one of these combination units. To replace the impeller do I really need to remove the entire unit? I saw a YouTube video where it seems you do not... can I just loosen the hoses and then the screws to remove the housing?
 
Thank you. I have one of these combination units. To replace the impeller do I really need to remove the entire unit? I saw a YouTube video where it seems you do not... can I just loosen the hoses and then the screws to remove the housing?
I took the whole thing out as it was a pia to try to get the bolts back in impeller housing the first time.
 
Is it difficult to remove the entire assembly? I’m debating between trying it myself and hiring a marine mechanic. I’d like to learn because I do lots of other types of work on the boat myself but I also don’t want to screw up the engine. I looked around the thing and it wasn’t obvious to me where it’s bolted and how to remove it.
 
It's really not that hard to take the whole pump out. But when I changed just my impellers, I just disconnected the 2 water hoses, then the long bolts that house the impeller to replace the impeller. Pump assembly stayed bolted to the bracket. This all depends on how much room you have. I had quite a bit in my 37 DA.
 
This is an issue that came up on the old board, and I thought I would repost the information here that we learned.

On many 7.4 liter engines used in the mid-90's (I don't know the date range), Merc had a design where the sea water pump and the fuel pump were on the same belt driven shaft. The sea water pump part of this are typical. You should change the impeller frequently, normally annually. But there is not much mention of what to do with the fuel pump. Plus, what you need to do is more than what is written, I believe.

First, here is a picture of the whole unit removed from the boat. When you do impeller maintenance on this thing, you might as well go ahead and remove it, at least every other year IMHO.

pump_assy.jpg


In the image above, I have labelled where the plug is that allows you to check the level of the oil in the fuel pump housing. Just below that you can barely make out in circular writing "See owners manual". Not exactly a big red flag!

More on that later, but let me deal with the impeller first, because that is the easy part. In the case of the unit I have shown, the impeller housing is a single piece design, the newer design. Probably most of the older multipiece units have been replaced with this type by now.

So you can just remove the bolts that hold the impeller case to the rest of the assembly, and pull the case and impeller off the shaft. Here is what the impeller will look like still in the housing. You will normally replace the impeller, and maybe the housing too if it shows internal wear or has other damage.

impeller_et_housing.jpg


Here is what the shaft looks like where you just removed the impeller housing, impeller, and wear plate. Nothing surprising here. There is a bearing and seal inside there around the shaft, and in this photo there is no evidence of a seal leak.

impeller_shaft.jpg


Between the impeller and the fuel pump base there is a removable wear plate. It looks like this, when worn. At the time, I think I did not have a replacement on hand, so just flipped it over when I put it back together to put the worn side away from the impeller.

pump_wear_plate.jpg


When putting the impeller in the housing, I think you should put in some lubrication to keep it from running dry before water pickup starts. Not sure what you should use.
 
Hi Dave this would be a great helpful thread but for some reason I can not view the images is there a way that I can see the complete thread sincerely Steve D
 

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