Mechanical Fuel Pump HELP - 260 Mercruiser
 

Sight-glass had residue in it, and after wiping it out, running the boat for several more trips, it got more in. Fact manual (My vintage is 1979-1980 350) says to change fuel pump when you see fuel in the sight-glass (Now it runs through a tube to the carb I believe). SO, even though the engine was running, I decided to avoid having a breakdown due to a fuel pump failure. Ordered a new Sierra pump off Amazon. Hooked it up, but forgot to fill the fuel filter back up after having removed it.... maybe that was my down-fall? Anyway, engine did not get any fuel delivery, no matter how many cranks. Primed the carb with some fuel and it fired up right away and died momentarily after. Took the fitting off at the carb and put a rag there to catch any fuel. None. Blew air back through the line from duel filter to tank, just to make sure no obstruction and I could hear it bubble back into the tank. Hooked up again and still no delivery. Figured maybe I got a bad pump. Ordered another one... same issue. Was careful to make sure the arm was under the push-rod but still no delivery... even though I filled the filter back up with fuel.

No idea what to do now... Does the system need further priming somehow? Seems boats and even cars run out of fuel, which would suck the lines dry, and they start again when the tank is filled. But what are the odds I got two bad pumps? I would put the old one back on, but in all my curiosity to see the interior and spot where it might have been failing, it is in pieces or I would try it, just to trouble shoot pumps.

Help....! Thanks, Doug

My first thought is the fuel pump pushrod length is too short

All sbc chevys should be 5.75 inch soprobably not the issue. Make sure there are no leaks on the suction side or it wont prime

Thanks for your input
 

Well, keep i mind it actually worked fine before I got my fingers on it! BUT, I did use a Sierra pump rather than the OEM, and the end of the arm is ever so slightly narrower.... guess I could try an OEM pump. As for suction, good point but I did re-seal the flare fittings into the pump with teflon tape and then the actual flare fittings are completely snug. I wondered if I should try to check if the push rod is moving...? Guess I could have someone crank the engine while I look in the port? VERY weird.

Thanks a bunch for offering some input on this.

You don't use teflon on flare fittings. The thread is not the seal. The flare is. And if you got Teflon in there, you got a leak. Take the Teflon out.

No worries, I didn't clarify the tape was on the female fittings screwed into the pump. The flare connection into those females have NO teflon tape. I appreciate your feedback.

- Doug

That is pipe thread. That is where Teflon belongs.

Your pump should be Merc part number 8M0058164 and the Sierra one should cross to this one. Pull the pump and pump it to make sure the inlet side is actually the inlet side, you should feel some suction. If you do, install pump and connect line going to the fuel tank to a 5 gallon gas can

Thank you, will do
 

I appreciate the help! I'll try it. - Doug