Yam 250hp, keeps blowing LOW pressure fuel pumps ...

[DaleH]

This is a friend's engine ... and I'm not a Yam guy ... Any ideas?

I continue to blow low pressure fuel pumps and I am starting to believe I have an internal problem, perhaps experiencing too much air pressure coming out of the small hole on the side of the block which powers the pumps.

SYNOPSIS:
The engine shuts down at high rpm. I do not have a vaccum tester but I can not believe I have a fuel supply problem. I could replace the blown pump and run a separate tank but have no done that yet.

DIAGNOSIS ATTEMPTS:
On the last set of pumps (which I ordered on line versus a local supplier so I would get a different lot) they blew after 1-minute at 4800 rpm. I removed them and noticed that fuel came out of the hole in the block on the top fuel pump, however the pump itself was not blown. I know this because I removed the pump from the block and if I squeeze the bulb hard I cannot get fuel to leak our of the pump, so I know the diaphram is ok. However the first fuel pump down the bottom was blown, fuel just comes right out of the hole in the pump itself.

Data Points:
Tank inspected and clean
Anti syphon or check valve at tank replaced
Fuel line to primary filter/water separator replaced
10micron filter replaced.
Filter on side of block inspected but not replaced
One way check valve between filter on side of block and first low pressure fuel pump replaced
All three low pressure fuel pumps replaced ....twice
Compression is 100 lbs on 4 out of 6 pistons. The other two are 102 and 105 lbs.

 

[Brent]

I dont have this OB

I would purchase a fuel pressure guage and check pressure before pumps and after VST. The check pressure with key on (should be high) and after 5 sec should drop

check with Andy at SIM

m2cw

 

[DaleH]

check with Andy at SIM

Have already emailed him ...

I'll report back what we find out ...

 

[Cb_usmc]

Are they Yamaha pumps?? If not they are worthless. I believe Mallory makes them and they fail within 30 minutes of use. I had 1 bad right out of the box from Yamaha last year. If they don't go together perfectly they can tear the diaphragms. Also were the pumps overtightened when they were put on? Does he have a lean sneeze? One sneeze can tear the diaphragms also.

 

[parkerjon]

Are they Yamaha pumps??

I agree. Thats the first question. 15 years ago we rebuilt an 18 cyl. Alco diesel. We used after market fuel tubes for the injecters. Everyone of them leaked within a few hundred hours. Replaced them with a different mfg (forgotten). and were fine.

BTY, I currently have a 2001 Yamaha 250 ox66 and installed new yamaha lp fuel pumps 3 years ago and still going strong. I keep a set of 3 new ones onboard only because of fear from the internet chatter that they will fail.

 

[DaleH]

All OEM Yam pumps ...

 

[Cb_usmc]

Does he have any kind of lean sneeze? If so sync and lync time. Had a lean sneeze last year which resulted blowing a diaphragm on the pump. Throttle positioning sensor can become out of specs. Get the test harnesses and put it in specs. a sneeze can blow the diaphrams pretty easy on the big yamis. I believe SIM has test procedure on web site.

 

[DaleH]

FYI ... troubleshooting info provided by Andy (SIM) of http://www.shipyardisland.com/

Andy, by the way ... is AWESOME for Yamaha motor and part support! He posts and contributes all over the net !

"I would be leaning towards a lean running condition. If the engine backfires, sputters ect that can blow out a diaphragm. I’d ask if that’s happening. VST fuel filter has not been serviced, or the O2 sensor. I would also make sure the injectors are spraying correctly."

 

[finfish1]

I replaced two one year.
The first was warrantied, the second I paid for.
After speaking with Yamaha, they paid for seven or so previously under warranty since the F250/2005 was new.
I flushed/cleaned the tank, and had the "F' filter changed. ( small in-line filter)
THEN I NEVER ran the engine without Marine Stabil and $$$ Ring-free.
I wasn't a believer before.
I also never start the engine cold before pumping the primer ball.
Haven't had a trouble since, however I did blow a hole in the block this season, of course un-related.
Is this operator running an ethanol treatment?
Thats the key, those pumps will rust over night ( and fail) from moisture in the fuel.
I've seen it.

Reel Job