98 250 ox66

[Salty Dawg]

Took it into the shop with a rough idle & smoking,miss/sputter feel on accel til around 1200 rpm's,would not go over 4k rpm's at WOT. The shop replaced LP pump diaphrams, cleaned injectors,O2 sensor,regulator screen & VST filter,adjusted TPS from .6 to .5 volts, replaced water seperator filter & checked pick up tube in tank. The fuel lines were replaced last year with primer bulb, new spark plugs & boots,water pump & t stats & pop off valve. The compression tested good. I ran the boat last weekend & the engine idled smooth with very little smoke, on accel it was also smooth & took off good,got to 5k rpm's & could feel it bogging down at full throttle & full trim, what I did notice was everytime I hit the trim up switch, the bogging would go away until I let off the switch. The shop thinks it could be the main relay but is not for sure. Any thoughts on this? Thanks in advance. The engine is a 98 250 ox66 s250txrw.

[99yam40]

I do not understand how drawing current with the T&T motor would help get more fuel pressure to rail if that is what is happening.

Should be easy to monitor fuel pressures and maybe voltage and current to fuel pump while problem shows up to see if that is what is happening

I have read about the T&T current draw dropping voltage to ECU and causing missing before but not correcting it

[Salty Dawg]

It felt like for a second when trimming the motor up that it would not bog down, you could hear the change in the motor when trimming up, if I held the trim up button it only lasted a few seconds then bog down again.

[rodbolt17]

start checking battery connections, quit hunting the main relay ghost.

as the ECU sees battery voltage dropping it compensates by adding fuel.
it accomplishs this by increasing injector on time.

[Salty Dawg]

Thanks for the info, was going to check battery connections next time over to storage. The shop stated they have one in that is doing the same thing mine is doing & the main relay took care of the other motor. I just dont see a main relay causing this, but a poor connection could.

[99yam40]

the motor must be running low pressure or something if bogging and the adding of fuel by ecu during low voltage picks up RPM

Just thinking out loud

[Salty Dawg]

They cleaned the VST filter as they did not have one in stock at the time, one has been ordered.

[99yam40]

but does the rail pressure drop when bogging?
That is what needs to be checked to see if there is a restriction somewhere
Not just hoping that screen is the problem causing the bogging

[Salty Dawg]

I dont know about the fuel pressure if it drops or not or if they even got up to speed to feel what I was feeling, when I say it bogs, it does not drop any rpm but will not gain any, I can tell the difference in the sound it makes that something is not right.

[99yam40]

my thoughts are you have at least 2 different problems
one the bogging and the other the voltage drop

[Salty Dawg]

Update: went thru the electrical connections starting at the battery working my way to the engine. All conections were good,clean & tight except for the ground wire going to the trim relay was loose. The weather was bad so no boat ride today, hopefully next weekend.