'95 Mercruiser 350 Mag Mechanical Fuel Pump Replaced - No Pressure

ThndrSki

ThndrSki

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May 27, 2011
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I was getting no fuel pressure previously, checked for issues with blockages to the tank, check valve, etc. All proved negative. I also hooked a line to the inlet side of the fuel pump and nothing.

I replaced the fuel pump by holding the push-rod up in the cavity and sliding the new pump in and tightening the bolts. After minutes of cranking bursts, I checked the fuel water separator and nothing was in there. Hooked a fuel hose up to the inlet and nothing again....

I then noticed a ton of oil under the motor coming from the oil filter; apparently it had rusted through and bled everywhere. This was on my list of things to change after the fuel pump (fresh oil/filter).

My question is, I can't tell if the pushrod operates off of oil pressure or directly on the cam lobe. Could I have somehow "slipped" and let the push-rod fall or slide over and the fuel pump bolted on? It went in easy....

First thing I'll change the oil and filter, but what gives?
 
Bt Doctur

Bt Doctur

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Aug 29, 2004
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19,133
the mechanical pump uses a rod and its impossable to miss it installing a pump, I would check to se if the pushrod moves when you spin/crank the motor.
could have a bad cam.
 
ThndrSki

ThndrSki

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Yes I couldn't miss the pushrod as I had to hold it out of the way for the pump to go into place...
 
ThndrSki

ThndrSki

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Is it possible I could have installed the pump and let the pushrod fall all the way back down?
 
Bt Doctur

Bt Doctur

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I think that's unlikely, all my years of gm motors never missed one.
 
B

buzzm19

Petty Officer 2nd Class
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Dec 14, 2009
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152
if the cam lobe is ok I ran into this problem about four years ago, two new fuel pumps zero pressure, the old ones I pulled had only 4lbs. I compared the two and found a manufacture defict, the new pump arms were bent low enough that the rod could not push the rod, I wound up changing the top parts and installed had 8lbs pressure. And of course the pumps were made in china, its a little hard but you could bench test and see if the pumps are working and you can use plain water. hope this helps Buz
 
ThndrSki

ThndrSki

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I purchased an OEM pump but I can definitely check to see. This is very strange.
 
Fun Times

Fun Times

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ThndrSki said:
I purchased an OEM pump but I can definitely check to see. This is very strange.
Click to expand...
Unfortunately some of the OEM pumps have been known to be defective from new more than once.:( In this case ignore my signature line below and try a Sierra Marine, Airtex, or Carter.

Search online for marine mechanical fuel pump or search your OEM part number in here, Marine Fuel Pumps - Mechanical & Electrical - iboats.com
 
Fun Times

Fun Times

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ThndrSki

ThndrSki

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After changing the oil and the rusty leaking filter, I filled the fuel/water separator all the way to the top and shot a couple squirts of gas into each of the 4 barrels of the carb and voila. It started up and ran fine for a long time on the hose. I guess the system was so dry it wasn't able to prime itself the first time.

Thanks for the double checks, I don't believe it's possible to put the mechanical fuel pump on there and miss the rod, so I didn't even check that. I'm using the OEM so maybe I'll report back in several years how it's doing. Thanks for the double checks and the feedback, I just wanted to post a resolution to this problem.
 
NHGuy

NHGuy

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Thank you very much for reporting your solution. So many folks never report back.
On those ones I wonder if there was a resolution or if they gave up, or solved their problem a few steps later.
 
ThndrSki

ThndrSki

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Not a problem, I always like to help my "fellow boater" out when I figure the problem. This was my first time replacing a mechanical fuel pump (I have done quite a few electric ones) and I also replaced the 3 foot fuel hose from the top of the fuel tank check valve to the fuel water separator. I imagine with a completely dry pump this needed some prime, and I'm sure a "dry" fuel pump won't work as well.

Thanks again, these forums are a HUGE resource along with the FSM, but the FSM basically just said "Replace and Torque Bolts"! Ha! :)
 
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