Still chasing fuel issue…4bta

[Tom Jerome]

Evening,

I have been having a lag in the port engine spooling. Ive done all the low power checks that i am able to. Replaced the lift pump and the return check valve as the pressures were on the lower side. Still having a 40 sec lag of it spooling. Boost pressures are same as the starboard and egt are about the same. Port runs about 916 wot and starboard is 890. The port losses prime when sitting for 48+hrs but cant find it. Attached are the numbers from running test with port only starboard only and both engines. Test were ran at various rpms and spooling was checked from dead stop to wot out the hole. The starboard when ran alone spools in 20sec or less. The port spools i  40 sec on one run and then another run it took 2:30min, had to back throttle to halfway then it spooled. When the engines are ran together the star takes 9sec to spool and the port took 20 to 30 sec. Not sure where to go from here, thoughts are injection pump timing or aneroid. Is the loss of prime related?? 

 

Also maybe unrelated but these 4bta 250hp should be getting to 3100rpms. My WOT is only 2800rpms on both engines, verified with phototach. Orginal prop pitch from factory was 19×23 mine is 19×22.5…. is this a prop issue or possibly from poor performance or is there something limiting my throttle/engine to that rpm?

Thanks for the input…

Topic

[donald roth]

Or you could blow in the return line, if it bubbles, it’s submerged.

[Mark Tripi]

It does not take much to lose prime. One area I have had this happen on my 4BTAs is right at the connection between the return line and the injector, the copper washer. With a cold engine pump up your fuel system using the primer pump. When the pump gets hard to push check those connections. Feel them with your finger and see if you get any diesel fuel on there. 

[Dan]

s2 = s2 yacht (boat builder)

108  = is capacity

AS = starboard

AP = Port

So none of the above is an accurate description of of how your tanks where shipped from the manufacturer  ie fuel fitting sizes and submerged fuel return. They all have the same senders.

Pursuit/Tiara ordered the tanks  from FMT to suit the build (gas or diesel)

Your looking for a six digit code as shown in this pic as shown in the build paperwork for this particular boat

[Tom Jerome]

tanks

Looks like these are the tanks i have from a earlier email i send when i got new senders to the manufacturer

S2-108AS and S2-108AP FMT fuel tanks

[Dan]

Fuel returns

Tom,

I have the same boat/engine combo, my boat as it left the factory was not fitted with submerged fuel returns. It caused me much grief over the years.

Look at the tag on top of the tanks if you have ” FMT – 105P S2 P/N 319332 stamped on the ID tag you do NOT have submerged fuel returns.

[Tom Jerome]

thanks

I will check with the tank manufacture to  see if they have a schematic design of these tanks. The injectors were replaced about 20 months. Could be a small leak there somewhere…. I guess best way to isolate from the boat or engine side would be to place the intake line of the engine right at the lift pump into a can on diesel and see if it still loses prime?

[Tony Athens]

Look at the picture(s) … A submerged return for YOUR fuel system design is a REQUIRMENT for your exact issue.. Just because it does not happen on both engines is not applicable.. Just do it and don’t concern yourself with the “why”..    But if you must, just ONE injector that leaks after shunt down will leak air back up to the injection pump and cause the fuel in the engine injection pump to leak back to the tank level..  Result= hard / slow starting

Think about it. 

[Tom Jerome]

1. Will get the pitch taken out and go from there. Not sure i fully understand the return line question. There is no way to see inside the fuel tank though so I have no way to tell. The return lines go to fittings welded onto the tanks. 

[Tony Athens]

Loosing prime?————————–Are both return lines submerged to close to the bottom of the tank?   That is a yes or no answer..

Slow spooling? Do not  know at this time, but until you are propped to reach 3100+, none of that matters..

 

[Tom Jerome]

Reprop

I can agree to that. Why though did it just start slow spooling on port though within the last 9 months. Props were redone 2 yrs ago from 19×24 to 22.5… any thoughts as to why the port losses prime?

[Tony Athens]

Your issue IS NOT FUEL————————–At this point, the answer is real simple– Prop down (3″ of pitch) t0 19 x 20……………..You are asking way to much from your engines…………3100-350 is the NUMBER wen loaded for bear…………… All you numbers & symptoms point to that.. If you are you in “DENIAL”, better rethink ??  If so, no one will be able to help

[Author]

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