F150 TXRD losing rpm till you pump bulb

[boscoe99]

I would plumb a piece of clear plastic tubing into the fuel line somewhere close to the inlet of the mechanical fuel pump. You might be sucking air causing the fuel pressure to fall off. If you see air bubbles in the clear tube you know that you have a problem.

[99yam40]

seems when someone asked what fuel pressure was when problem happened you said

just a little lower then 38 hard to tell exactly on the water my needle jumps around a bit.

now you say about 20 psi.

From what you have written so far I am with boscoe99 with sucking air causing the VST to run out of fuel

[gunz@pc]

Just had to see what would happen so I took my whole throttle body, VST, fuel rail, injectors yada yada of my engine (that runs like a raped ape) and guess what drummm rooolllllll please it still does it.... oh well back to the drawing board... must be time to repower haha.

[zenoahphobic]

Just had to see what would happen so I took my whole throttle body, VST, fuel rail, injectors yada yada of my engine (that runs like a raped ape) and guess what drummm rooolllllll please it still does it.... oh well back to the drawing board... must be time to repower haha.

I presume you did something with all those bits that were taken off.
Like? And put them back.
Sorry can't see clearly my imagination still stuck on this "raped ape" - don't have that expression back home

[rodbolt17]

this aint hard.
if you can pump the primer bulb and it works, fix the lift pump/low pressure fuel circuit.
if the VST cannot get fuel guess what, the pressure drops and the motor quits.

by pumping the bulb your simply using the bulb as a low pressure lift pump.
so either your sucking air or the pumps are not working correctly.

[gunz@pc]

I know it ain't hard and a thread this long you probably didn't notice this from my previous post:

"Took both fuel pumps off my motor (that runs like a rape ape) put them on his motor does the same thing"

As a mater of fact tried 2 more after that. Thank you though.

[rodbolt17]

not saying its the pumps.
however

[gunz@pc]

Capt Solo did change the bulb and oetiker clamped that whole mess to the filter made sure the o ring was in the fuel cup and the cup was seated well.

[boscoe99]

You need to plumb a clear section of fuel hose and a vacuum gauge into the fuel system just ahead of the first fuel pump.

Do you see any air bubbles in the clear section? That would indicate a hose leak somewhere between the tank and the gauge. The pump will suck air, not fuel. Air, instead of fuel, to the VST will cause the VST to run low on fuel at which time VST pump pressure on the rail will fall off.

What is the vacuum reading when the fuel pressure falls off?

I once had a fuel hose that was disintegrating internally. A flap of the hose liner would sometimes restrict the flow of fuel. Some times it would not. With the vacuum gauge installed the vacuum reading would soar when the flap of hose liner restricted the flow of fuel. That or something similar may be happening in your case.

Your fuel hoses are roughly 10 years old. They don't last forever.

[fisher not catcher]

unbolt the LP pumps from the block, leave all fuel hoses connected, pump the bulb if fuel comes out the back replace all three. actually if they are more than 3 years old just replace them +/- $35 each.
Heres a link for the check valve its easy enough to by pass.
http://www.marineengine.com/boat-for...5&d=1347001433

[boscoe99]

unbolt the LP pumps from the block, leave all fuel hoses connected, pump the bulb if fuel comes out the back replace all three. actually if they are more than 3 years old just replace them +/- $35 each.
Heres a link for the check valve its easy enough to by pass.
http://www.marineengine.com/boat-for...5&d=1347001433

You may be confusing the OP's Yamaha with a different Yamaha.

The F150 only has two lift pumps. They are camshaft driven, not crankcase pressure pulse driven.

The F150 pumps are $220 each by the way. But I don't think they are the problem given that he took the pumps from his good motor and installed them on his sick motor with no change.

[Nautical]

Did you replace the fuel line from the tank suction through the bulb ,and all the way to the lift pump?When you ran the portable tank did you use any existing fuel engine lines or did you use another fuel line connected to the lift pump.

[gunz@pc]

Boscoe 99 gonna give that clear tubing trick/ vac gauge trick a try and check the fuel hoses and connections again.

Capt Solo I'll probably do the injectors again to be safe but idles fine and goes to the magic RPM no problem can get 5700 if I pump the bulb the way its propped right now.

Nautical when I ran the portable tank I went right into the "t" fitting to the lower right of the lift pumps, ruled out bad gas did ethanol test and our fuel in the portable tank is fresh and good to go...

Thanks guys for the input I'll have to post once I get her figured out..

[TownsendsFJR1300]

Just a side note that may help..

After the boat sitting for several months(run on muffs inbetween), I had a similar issue with my F150. it hit about 5k, and the RPM's started dropping, no alarms. Never done this before.. Brought it back up, did it again... One more time, it went to full throttle and did so the rest of the day, several times..

I run RingFree regularly but "think" just an injector got something stuck in it and finally blew it out. Next time I go out, I'll add just a little more RF just for S&G's.

BTW, I've never pulled the VST, changed the filter, etc.. I have drained the VST when I ran Ethonol and since stopped using it(ethonol).. I eventually got all the ethonol out...

[gunz@pc]

Boscoe wins!!!!!

Thanks for all the insight on this one and she is solved, runs great now. For those that are interested clear plastic tubing trick did it. Sorry Boscoe didn't have a vac gauge handy.

Hooked up a piece from the main tank to the filter on the engine at idle and to around 3500 very few bubbles up to 4800 it was like champagne flowing thru there so started retracing the step to the boat, one of the oetiker clamps pinched the hose in a funny way allowing air to get in, apparently they changed the design of the clamp. Changed that less bubbles kept going to the tank tightening and moving hoses found another. Took the clear off and put it to the lift pumps at the "t" very tiny and the rpm's started to pick up and run great. But while I was in the front I noticed the front filter cup had a piece of crap that made its way up there so took it apart changed the filter and cleaned the cup and you know what so say it with me..... IT RAN LIKE A RAPED APE... thanks for all the help and suggestions.. for those wondering about the 6 gal tank doing the same thing bad/ lose connections... KISS