excessive fuel pressure

swampy2646 · Sep 22, 2009

i have 5.7 merc. q-jet, mechanical, dual tanks with a T type crossover. rebuilt carb. new fuel pump. after figuring out my ignition problem i'm starting a new thread on my pre-existing flooding problem that happend the same time as the ign. problem. after starting, about 30 seconds of running ,gas starts pouring out of the top of carb. upon shutting her down i can hear the pressure and see the fuel still pouring down the carb. i swapped out carbs with same results. problem also happend with old fuel pump. i can somewhat regulate it by just cracking the T a little bit to allow less gas to the pump. i checked the tank vents and they are ok . where is all this pressure coming from? i also brought carb back to shop and it was tested at 10 psi and it held.. any ideas???? thanks Pete

Bondo · Sep 22, 2009

Re: excessive fuel pressure

Ayuh,... Install a fuel pressure gauge, after the fuelpump,+ Check it.... 5 to 7psi is what you Should see...

swampy2646 · Sep 22, 2009

Re: excessive fuel pressure

im assuming its gonna be high, if thats the case, what next??

Bondo · Sep 22, 2009

Re: excessive fuel pressure

Ayuh,... It might mean you have a Bad fuelpump I guess...

John_S · Sep 22, 2009

Re: excessive fuel pressure

FWIW: Last season I had a similiar issue (only at idle and not as much fuel) and installed a gauge and it was over spec at 9-10psi. Purchased a regulator for this season, but didn't install. Fuel pump died, didn't pump at all, this season. Replaced with new pump. No issues at idle, but I didn't reinstall gauge to check pressure.

swampy2646 · Sep 22, 2009

Re: excessive fuel pressure

how can i have 2 bad fuel pumps and 2 bad carbs. is that possible???? john s.....you mentioned a regulator, i have a mechanical pump....... also you have to get pretty creative to splice in a fuel pressure gauge with steel fuel lines.

Bifflefan · Sep 22, 2009

Re: excessive fuel pressure

swampy2646 said:
how can i have 2 bad fuel pumps.

Those kids in china just dont rebuild stuff like they used to.

swampy2646 · Sep 22, 2009

Re: excessive fuel pressure

yeah... i shoud'a went with siera one instead of the quicksilver. i probally wouldn't be twisting my body like a contortionst for the third time, and i would be 40 dollars richer!!!

John_S · Sep 22, 2009

Re: excessive fuel pressure

swampy2646 said:
john s.....you mentioned a regulator, i have a mechanical pump....... also you have to get pretty creative to splice in a fuel pressure gauge with steel fuel lines.

I have a mechanical as well. I have a tubing cutter, tubing bender, and flaring tool, that along with the fittings shouldn't have been hard. The regulator I purchased doesn't have any stamping for CG approval, but not 100% sure it is required on it. I will hook my gauge back up and if psi is within spec, won't bother with the regulator. I used a short tubing piece from the pump, along with a temp rubber fuel line and Tee to do pressure reading.

swampy2646 · Sep 23, 2009

Re: excessive fuel pressure

ok, so i did a fuel flow test, the thing pumped 1/2 gallon in about 10 seconds, which is about 10 times more than it should have!!! this probally means the pressure is too high also??? correct??? its a brand new pump.

Apollo75 · Sep 23, 2009

Re: excessive fuel pressure

This isn't a High Performance Carter fuel pump or equivalent is it

You need a Viton needle and seat --- a new float ---

Keep those keys in your pocket until you check fuel pressure

Have Fun

OFM

swampy2646 · Sep 23, 2009

Re: excessive fuel pressure

thanks apollo, im gonna rig something up for that. but does that mean the excessive flow is irrevelant, and could not cause my problem??

Apollo75 · Sep 23, 2009

Re: excessive fuel pressure

Volume means little as long as it is enough for those two Q-jets your feeding

Vroom, vroom

As long as the volume is above specifications ---- okay --- could be a pressure relief problem in the pump --- check first -- I have good luck with Viton needle and seats and always change the float when the carb top needs to come off.

I wish you well and will help when I think I can

OFM

JustJason · Sep 23, 2009

Re: excessive fuel pressure

post your engine serial number and the part number of the fuel pump thats on the box.

swampy2646 · Sep 23, 2009

Re: excessive fuel pressure

the part # on the box is 861678A1 i re did the engine with a new long block it was orig. a 1991 5.7 mercruiser 4 barrel Q-jet,

JustJason · Sep 23, 2009

Re: excessive fuel pressure

well thats the part number for a fuel pump for a 305/350 so it should work. Unless somehow the wrong pump got in the box, uncommon but it happens. Are all of your fuel lines, starting from the tank, ending with the steel line at the carb 3/8ths ID?
Are all the barbs 3/8th ID?

Could still be a defective pump... it happens. 1/2 gallon in 10 seconds off cranking is an awefull lot.

swampy2646 · Sep 23, 2009

Re: excessive fuel pressure

yeah jason every thing checks out, im gonna do pressure test tomorrow and hopefully get to the bottom of this. thanks, pete

swampy2646 · Sep 24, 2009

Re: excessive fuel pressure

problem solved!!!! did the pressure test on the brand new fuel pump, 21psi !!!!!!!!!!!!!!!!! put the old one in, runs fine. now comes the part that sucks, my friend at the parts store told me (on the cuff) that he had taken back 4 or 5 pumps for the same reason!!! quicksilver screwed the pooch somewhere. Thanks to all for your help. Pete

deadstick · Sep 24, 2009

Re: excessive fuel pressure

swampy, im glad u got it going! happy boating

excessive fuel pressure

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