Mark IV fuel pump sprung a leak

handfulz28 · 11-20-2006, 09:58 AM

1991 454 MAG
I replaced the raw water impeller and some hoses over the weekend and dropped it in the water to make sure everything was good. Started it up and saw a spray coming from down there and figured I needed to tighten a clamp or something. Get in there and smell the gas and thought holy crap, that was gas spraying out of there.
I knew it was rusted up and already have a new one to replace it, but I'm new to mechanical fuel pumps so any tips are greatly appreciated. The pump has the fittings already installed, but do I use thread tape or pipe dope for the hard lines fittings?
The big cooling hose used to leak and sprayed water all over down there so everything is rusted/corroded. I did a coat of PB Blaster to hopefully loosen stuff up.
Thanks,
Michael

rdoactive · 11-20-2006, 10:55 AM

THe hard line is connected to the fuel pump fitting with an inverted flair compression fitting. No tape or thread sealer is used on that.
There is probably a brass fitting which has the inverted flair on one and and threads into the pump hosing using NPT on the other.
The NPT fitting into the pump housing needs to use tape or sealer.
Gary

Wobble · 11-20-2006, 11:30 AM

I have had better luck with tape on gas line fittings.

There is push rod inside the block that must be pushed back up before you can get the pump onto the block properly.

Be sure and use a gasket sealer on the pump to block gasket as there are only two bolts and they are prone to leaking. (I prefer Blue Hylomar) But any type will suffice.

Make sure your fittings are tight in the pump before attaching your fuel lines.

Make sure you have the marine pump with the vent line back to the carb

handfulz28 · 11-20-2006, 04:11 PM

Thanks guys. It's a Merc pump so it came with the pump fittings already installed; I'm afraid to verify the tightness since they're in their with the "factory red" thread seal.
Hmm...no gasket in the box, have to go back and see where that went. Where can I get Blue Hylomar? Is that just Blue RTV (permatex?)
I got the old one off, barely. Looks like it might have actually been the hard line to the carb that might have leaked; may never know for sure. But I couldn't get that compression fitting loose so I had to twist it off the hard line. Now I need a new pump-to-carb fuel line...

Thanks,
Michael

Wobble · 11-21-2006, 10:33 AM

No need to tighten if factory installed, I have seen metal line crack along seam. Hylomar doesn't stick like RTV, either is good, available at most auto parts next to rtv. Standard GM BBC or SBC fuel pump gasket

handfulz28 · 11-21-2006, 02:12 PM

From bad to worse I tell ya'.
I wanted to go with AQP blue socketless hose from pump to carb but my search on OSO only confuses me as to what is USCG approved (pump to carb).
And that's after stoppng by a couple hose suppliers to see if they have the fittings to get it done.
I have no time or patience to learn how to flare/bend my own lines. Crap, I really want to get this done so I can use the boat.

rdoactive · 11-22-2006, 09:01 AM

Buy the hard line from Merc. If you're using the original pump and carb, it should be a direct replacement.