Fuel pump fail again!

72GT160

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On 4th failed pump in 2 years. I have SB 350 i put in new 2 years ago (Sundancer 260). At that time put new Sierra pump in (i know, i know) which failed, lost pressure. Retailer would not refund, but warrantied pump with a new one. Put old (known good) pump in while waiting for warranty, got about 10 hrs out of that, lost pressure. Put warranty pump in. This spring doing some testing with ignition and was getting 12psi @ 4000rpm. Fuel was spraying out of venturi as soon as secondary opened. So, picked up an OEM Mercruiser pump from stealership. That worked good for 14hrs. Lost pressure again! 3psi at idle now. Starves about 2300rpm.

So, i went through the whole system. Pulled fuel filter; poured into glass jar, clean, no water. Put new filter on, same pressure. Pre-sediment filter has just a little bit of specs, this is from about 50hrs of use, view that as normal. Pulled tank sender, inspected tank, clean as a whistle. Pickup tube clean and clear. Vent is clear. Tank has never been to the varnish point, no history of that. 3/8" Fuel lines are new. Steel line from filter to carb w/ inline pressure sender.

Been looking through history here about pumps failing. was thinking electric? but that has it's own issues and modifications. Holley mechanical pump? Go to Summit racing and the reviews state that some of their pumps fail and are from china. Stealership states they will get me new pump, whenever it comes in...Or they will return my money. I don't know which direction to go. The rate of failure on pumps here and other confirmed places is staggering. Is there not a pump manufacturer out there that can produce a long lasting pump? Any suggestions before i roll the dice again?
 

alldodge

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What is the serial number or at least the year of the motor?
 

bman440440

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S/N of engine would be helpful.. save yourself some aggravation and go electric... the conversion is not that hard... all you need is a oil pressure switch 805024, T fitting 28624 and fuel pump 805656A5... with some basic wiring and a few hours you will be on the water without any more worries... and you can get the sierra pump and save some $... I have over 2000 hours on one of mine and no issues
 

72GT160

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I don't have SN right now. Engine is from 1974, marine application. bman, ill take a look at those numbers, thanks.
 

alldodge

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doing some testing with ignition and was getting 12psi @ 4000rpm

Was not able to find the 74, but found the 77.
This comment gave me the indication of what might be happening. If your installing the pump without using the fuel pump mounting plate (item 4) then the pump rod is being moved to far. The extra distance increases the pressure above 7 psi and also pushes the diaphragm to far which causes it to rupture. It should have the mounting plate and two gaskets

http://www.mercruiserparts.com/bam/subassembly/31731/1594/4
 

72GT160

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Dodge, Thanks for replying. #4 plate is installed. I just took pump off and dis-assembled pump on bench. as well as old pump that had 12psi. I don't see any visible issues, diaphragm is in good shape, on both pumps. Inspected cam push rod. that is in good shape as well. It measures 5.75", is this a correct length?
 

72GT160

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Double checked to see if there is an anti-siphon valve, there is none. double checked vent is clear, it is...
 

alldodge

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5.75 should be correct. So the pumps fail, diaphragm is in tact, can you see anything that has failed?
 

72GT160

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Took both apart and took some pics but, they wont upload. Sierra pump looks in great shape from the Mercruiser pump. Merc pump looks like it was used and has some old crosion residue. Have you used SeaFoam as a fuel stablizer? After a couple years of none use the seafoam breaks down and leaves a white powder and sometimes etches on metal. Thats what it looks like on the merc pump. And the lower diapgram is bulged; where the Sierra is nice and flat. Other than that, i have no idea why these pumps failed.
 
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alldodge

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Never used seafoam (snake oil) in anything.

With the diaphragm being good on the sierra, guess the check valve must have stopped working
 

alldodge

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It's not a marine pump and not USCG certified, and it runs on 24V instead of 12V. Also states not cover if used in non-automotive apps
 

72GT160

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Ok, yeah, USCG cert. Believe that's the issue. I was doing some searching and they 'look' the same, i know there are differences, just wasn't sure. Local parts are hard to come by as most don't stock.
 

72GT160

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Engine is 1974 Chris Craft with engine# 620104... Last fuel pump pn is 8M0058164.

posted in CC section as well... Sorry for the confusion.
 
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alldodge

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Things are not adding up
The part number is listed for a 1983 to 1995 5.0 or 5.7 GM motor. I cannot find a 1974 GM 350 used my mercruiser, I can find a Ford 351 and 302. Crusader did have some uses. In any case I'm unable to find the serial number listed above in the Merc listings or the fuel pump used for 1974

Fun Times can you assist
 

72GT160

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Fun times, thanks for the reply. The engine came out of a 1974 Chris Craft XK19. Now in an 85 Sundancer. I am not familiar with Chris Craft made engines. The block casing numbers indicate a GM 350ci block. The manifold has a model# 350FLVHP with and engine# 620104... Everything about the block is GM 350 (marine) in my belief. I have yet to find a true parts diagram from that period from CC. So, most of the time when parts are needed I just go with standard small block Mercruiser parts.

The original fuel pump looks and physically measures the same as replacement part(s). Yet with 4 pumps going bad in a short period of time I would really like to figure why. The probability of error in the manufacturing process is high in these aftermarket pumps, but 4 just seems too much. With that said, all these pumps worked fine for a period of time, then failed. So, it's not that they just failed right away. Continuing on, I believe finding the correct parts diagram will confirm these are the proper pumps or not. Then I can move forward to see what other issues may cause failure. I've spoken with a couple CC dealers and after describing all the trouble shooting diagnostics I have done, the only thing we kept coming back to is the pump itself. One is checking his microfiche and will get back to me. So, the hunt is on to find out what the PN came on this motor originally and go from there.
 

72GT160

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Fun times, just called Robert from the link you gave. Original is a carter pump. Ordered one. Time will tell. I'll report back.
 

alldodge

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I'm unable to find 620104 in any of the places. None of the GM numbers start with a 6
The casting location should be on the left rear of the block below the distributor (No 3)
SBC Cast Number Location.jpg
 

72GT160

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The 620104 is Chris Crafts engine number. Casting is 3970010.
 

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