bsirk

I've got a 2007 502 MAG longblock running some of the older components off the previous 502 which was a '96, so therefore no cool fuel system but rather the dreaded VST system. This past Sunday the boat died while idling, and when trying to restart it would sputter and try, then nothing. Since I had just disassembled the VST () a few days before to clean the screen out, my initial thought was that it was malfunctioning again. See, the engine had been acting starved for fuel (minimally) earlier and had done the same thing while idling and running, which sparked my initial endeavor into the VST. However, when the boat died this last time, I immediately took the lid off the VST, and it was bone dry, which told me that the mechanical fuel pump must have been the culprit this entire time, and long story short, I had a tow in.

Last night I was able to pull the mechanical fuel pump off to inspect for damage, and here's what I found. I'm no expert, but is this actuator arm worn badly? In other words, is it worn too badly to function properly, because it seems that the little cam that drives it off the pulley doesn't have much of a lobe on it to begin with, so even a little wear could result in the arm not moving enough, thus no fuel pumping. You can see the metal rolled off on one side. Also, the arm didn't want to move much farther than maybe a 1/4 to a 1/2 inch at the end. Not sure if that's normal either. The diaphragm is is good shape, and there was plenty of oil in the reservoir around the little cam. Anybody had any experience with this? Am I just totally missing something else? Thanks.

VetteLT193

I'm not knowledgeable enough about this to give you a good answer, but if I were in your shoes I'd have a marine Holley electric pump on the way.

My Donzi was set up with an electric pump by the previous owner, it's my first carbed engine with an electric pump. All I have to say is holy crap I can't believe how much better it is. Starting is a breeze even after the boat sits for a long period. I will never go back to mechanical.

bsirk

I would have to agree with you, but the thing is my boat is EFI, which is running the VST which includes an electric pump. BUT, those things are so problematic, and I've read so many bad things about them that I was ready to do away with it and the mechanical pump a little while back and just run an electric pump. However, I've cleaned my VST and have learned how to keep it clean and functioning (fingers crossed), so for now I'll stick with it. But as soon as I made up my mind to do that, my dang mech pump went kaput! Go figure, it's a boat....

bsirk

One more thing> When you're running your mech fuel pump on top of your raw water pump as I am, do you have to use the Mercruiser designed actuator arm in a replacement fuel pump, or can you use an entire new pump (i.e. Holley Marine, or Carter, etc.)? In other words, what other brands are adaptable to be mounted on top of the raw water pump without having to re-use the Merc actuator arm, which in my case is obviously not an option?

Knot 4 Me

Looks like fuel dillution in the oil caused the arm to wear. I believe you have to use the Merc pump as the aftermarket marine fuel pumps I've seen have the longer arm for mounting directly to the block. You have to wonder how worn the lobe (eccentric) is on the water pump shaft that contacts the fuel pump arm?

bsirk

That's also my worry. I did shine a light down into the opening onto the shaft while my buddy turned the key over a few times to see if there was any visible wear on the shaft, and if it still had a lobe. From what I could tell, it looked clean, and there was some eccentricity (sp?) to it still, but whether or not it's enough, I have no idea. There was still plenty of oil down there too.

Does anyone have a pic of what a good actuator arm on the pump should look like? Or, maybe a pic of a good pump shaft too? Like I said, I've never personally been into the guts of this pump before now, so I can't tell if it's good or bad. It seems worn to me, and it also seems that the shaft should be moving more than it is capable of now (1/4 to 1/2 inch at most). Thanks guys!

Mbam

The stroke on that pump is very short. No question your arm is worn out. You really should plan on pulling the pump apart to inspect the shaft.

bsirk

That's what I was afraid of. Looks like I'll be tearing it down too. I did notice on mercruiserparts.com that the cost of just the replacement shaft in the water pump is around $110.

+1 for the B.O.A.T. theory......

Thanks again!

Thunderstruck

I searched the world over and found a cheaper supplier for the water pump mounted fuel pump. I am running one of these pumps right now with no problem. It is a direct replacement, just needs paint for $50 instead of the Merc $140. Also may need to rotate the head to line up with your fuel lines but I have to do that with the Merc replacements anyway. Even has the hose barb for the vent.

http://www.partsamerica.com/productd...rtNumber=60932

I would try a new pump before tearing into the water pump shaft housing. The cam lobe in the housing has a roller sleeve over it so you may be OK. Mine was.

bsirk

SWWWEEEEEET! That sounds like a worthy replacement for me. Hell, I'll at least give it a try for only $50! And the best part is, I can pick up the pump at an Advance Auto, and there happen to be three of them in my home town. Surely I can luck out with one of them. Thanks!