21v 350 MAG MPI Fuel Pump Replacement

[mdk681]

Hello all,

Last year my season ended with what appeared to be an intermittent fuel pump issue starting to show itself. When I would click the key one notch, I heard what appeared to be the fuel pump groaning and it sounded nothing close to what it usually does. I was towed into shore and put the boat on the lift to troubleshoot. The boat sat for a day and I tried to start it again and would not fire; it would crank but not even sputter in the slightest which steered me towards the pump. After trying multiple different days to get it started and the fuel pump not sounding normal when priming, I decided to get towed to the launch to trailer up.

After dropping the boat at my marine mechanic's shop, for whatever reason, the boat fired right up for him when he attempted to troubleshoot. He checked electrical connections all the way to the pump and said everything looked normal to him, and a tell-tale sign of a failing pump can be intermittent problems. We both agreed that it would be wise to go ahead and replace the pump this spring.

Well now that spring appears to be here, I plan to drop off the boat to take care of this project. My mechanic was concerned about accessing the fuel pump, as it has a plastic cover over it which is blocked by part of the starboard side hull from what I can recall. He thought it would take some serious surgery to access the pump, but I figured I would ask the folks on here if anyone has some insight. I recall him mentioning needing to remove a motor mount (I think?) to access the pump, which would require an alignment afterwords and a bunch of labor.

Any ideas on how to access this pump, and if it can indeed be swapped without taking anything major apart? I struggle to think that you would have to damn near pull the engine to replace a fuel pump. I have searched the forum for hours but can't find any write ups or tutorials covering this task. ANY help or insight would be greatly appreciated!!!

Boat specs: 1999 Tige 21v Riders Edition with the 315hp fuel injected 350 MAG MPI

[Hunter2050]

I had the same issue on my 01 21v. I took mine to the mechanic as I am new to boating and not savvy enough yet. They never mentioned having to touch the engine mounts. I think I was billed for 4-6 hours but that also including replacing a lot of other things.

[freeheel4life]

Try looking up Mercruiser "Cool Fuel". They are a pain to get to for sure. If your mechanic is trying to change the pump in the bilge then it sucks. I undo the hoses and unbolt the entire assembly from the block. Once on the bench you can change the pump and re-install the whole show. Still not a fun job but I have never pulled a motor mount to do one, but every boat and every mechanics reach is a bit different...cant say I recall removing a Cool Fuel on a 99 2100 sooo...

[mdk681]

Thanks for the insight. Searching the Cool Fuel definitely helped out. It sounds like the correct route to take is to remove the whole unit and swap the unit on the bench. Are the hoses difficult to disconnect when attempting the remove the whole unit? I just want to make sure I can bring my mechanic up to speed on the easiest way to tackle the project. Thanks again for the help!

[freeheel4life]

Sometimes they slide off, sometimes they need encouragement. I have a whole set of radiator hose picks for just this type of thing. The fittings on the cool fuel are just slightly flared, not barbed so they should come off after they get loosened up a bit.

[mdk681]

Got it - thanks for the direction. I just spoke to my mechanic and he recommended just replacing the pump with the cooler 'kit' as well. He said he looked into it further and will just unbolt it and change on the bench.

Thanks again for the help. Will report back with the results.

[mdk681]

Having some major issues getting to the bottom of this one and need some help. My engine serial number is 0L305479 and when I look it up on the Mercury Marine parts site, it shows me needing the 807949A1 fuel pump. Well this is all fine and dandy, but I have read that I should be replacing both the fuel pump (807949A1) and the cooler (861267A1) and that it all usually comes in a kit, which brings me to something like this: https://www.offshoremarineparts.com/8611-02.html

I called a local marina this morning, and they said that they looked up my engine by the serial number and there was a service bulletin saying to upgrade to kit number 862264A7, which is this: http://www.marinedepo.com/product-details.php?id=150

My main question is do I stick with the original kit, or go for the upgraded 'anti-vapor lock kit'? I have never had issues with vapor lock on my engine, so I was leaning towards the original kit. Any thoughts or input would be much appreciated.

[TeamAllen]

The anti-vapor lock kit should be adding a secondary fuel pump, in addition to the original fuel pump with cool fuel.

[mdk681]

The anti-vapor lock kit should be adding a secondary fuel pump, in addition to the original fuel pump with cool fuel.

I am guessing since I never had any issues with vapor lock in the past, this upgrade kit isn't needed?

With that being said, I guess I am wondering if I should replace the pump only or do the whole kit (includes fuel cooler) while I am in there?

[freeheel4life]

I think if you dig into it and try to buy just the pump it is darn near the cost of the whole kit. The "upgrade" is basically a transfer pump that puts fuel under pressure instead of vacuum. Liquids under pressure get their vapor point raised, liquids under vacuum get their vapor point lowered. This is one reason why fuel pumps are in tanks now as the entire line is now pressurized from tank.
This is just one mechanics opinion, but the cool fuel was a great idea to help keep gasoline below it's vapor point. Problem was that they mounted it next to a hot block and oil pan. Oil runs hot! The vapor lock will typically occur after a hard duty cycle on a hot day. Everything will be fine and then boat would get shut down for a bit. Heat soak would happen while sitting and cause vapor lock.

[mdk681]

I think if you dig into it and try to buy just the pump it is darn near the cost of the whole kit. The "upgrade" is basically a transfer pump that puts fuel under pressure instead of vacuum. Liquids under pressure get their vapor point raised, liquids under vacuum get their vapor point lowered. This is one reason why fuel pumps are in tanks now as the entire line is now pressurized from tank.
This is just one mechanics opinion, but the cool fuel was a great idea to help keep gasoline below it's vapor point. Problem was that they mounted it next to a hot block and oil pan. Oil runs hot! The vapor lock will typically occur after a hard duty cycle on a hot day. Everything will be fine and then boat would get shut down for a bit. Heat soak would happen while sitting and cause vapor lock.

Thanks for the explanation freeheel4life, that makes sense. I have never had issues with vapor lock to date, so I will just stick with the original style kit and skip the upgrade.

One other question - as long as I am doing the fuel pump, would it be smart to replace the fuel pressure regulator? The boat is nearing 19 years old and has never had the fuel pump or pressure regulator changed. I know it will cost me another 150$ for the fuel pressure regulator but it may be worth it due to the difficulty of accessing the whole assembly?

[freeheel4life]

I tend to come from the "If it aint broke don't fix it" school of thought. Then again, I wouldn't say its crazy difficult to access that assembly, I just call it wrenching in inboards so I guess it all relative...

[mdk681]

I have that same mentality. I ended up going with the OEM Cool Fuel pump/cooler replacement kit. I did not see the need to upgrade to the newer style dual pump system, as I have never had vapor lock issues to date. I keep my blower fan on the entire time I am running or parked at a bar so perhaps that has helped me out.

There was a OEM Mercruiser kit for around $400 and a Sierra kit for around $250. I ended up going with the OEM kit for the extra cash. Not sure if it was worth the money, but I figured it would be a good idea running as many OEM parts as possible. Here is a link to the OEM kit, part number 861156A02 for anyone else doing this project with an older V series:

https://nuwavemarine.com/oem-mercrui...0000-0m300000/

Having the pump swapped out this week so hopefully that does the trick! Will report back with results!

[Illiana]

Hello, I have a 1998 mag mpi 350 and replaces the fuel pump last year by myself with the assistance of the great feedback on this forum. Boat would start then do a lot of surging and suck and big hiss of air and die. Pump solved the problem. I think I got my pump on amazon or eBay for around 100-120. Only did pump and not the whole system. So far so good. I couldn’t instruct you beyond listening to the guys on this forum. Good luck.

[Illiana]

What I bought and the old one. New one matched right up. Have no ideas if this will help you or fit your boat. AB633844-59AD-4F22-B289-149F1419CB0E.jpg