F115 help....no power

[Landfall]

Bought a used 18 wellcraft with a f115 with ethanol issues. Been there, have the t-shirt.

This has me stumped.

New lower pressure pump. New High pressure pump, and all new filters. Racor, vst filter, and bowl filter. Reconditioned injectors. New line and primer bulb from the racor.

Drained tank, and flushed with clean fuel. Fuel coming out looks great. Added 20 gallons, startron and sea foam for good measures.

Took her out....won't plane. Runs like a top on the hose....idles and runs up maybe 2600-2800 fantastic. When I go to push her up on plane, she gasps.

Tried a fuel pressure test today. 38 ish at idle...holds this maybe a bit higher putting around 2000.

When the throttle is opened up, pressure drops to maybe 25. Might have gone lower but that's where I had them back off.

Pressure regulator? It does look kinda rusty, but I know that's on the outside.

I'm wondering if it's leaking, and when the injectors are not calling for much fuel, the HP pump can keep up.

Help...I'm starting to look foolish

Pete

[BIGELOW-]

I have 3 of those engines- all three have rusty pressure regulators, doesn't affect performance. Sounds like you have already done everything....

Is there a chance it's going into limp mode??

Have you looked at the pickup in the tank (possible its clogging)?

I would get a 6 gal auxillary tank and run it on that and see if it will plane, that will let you know you have a tank issue......

[BIGELOW-]

There's another post on here with a gentleman with a similar issue... he said if he takes the hose off the pressure regulator to the manifold it runs great... you may want to try that to narrow the problem.


Also, just remembered, that engine has a fuel cooler ( silver long "box" ) on the injector side... may want to disconnect the fuel hoses and spray some compressed air to make sure it's not trying to stop up...

[Landfall]

I thought about limp mode. My understanding is that limp mode typically retards the timing. The fuel pressure drops like a stone when it bogs down. I don't thing the ECU has the ability to control pressure. Also when I drained the fuel, I drained the tank via a 12v pump on the fuel line. I had flow that would drown a big block Chevy. I don't know what other that the regulator would make the pressure drop. If I had a bad injector I would see it on the plugs or even in the water with that much fuel.

Does this make sense?

[Bilge Rat]

With a new to you boat i would change the fuel lines.
The line from the tank may be good when you siphoned the tank but when the pump pulled a vacuum on it the liner may have started coming apart.

Check the lines between where you seperated it to siphon the tank and the motor.

Does the bulb collapse or is it still firm?

Had a F 150 that would idle fine but when you throttled up it would fall flat.
The bulb was firm. The line to motor was bad inside. Inner liner would collapse.

[Landfall]

Well....much like I thought, the fuel pressure regulator made no difference.

I will try a run tank today, but I really don't think that's it. The lines from the racor are new, and I drained the tank with and electric automotive pump from the racor, so it don't see any restriction there.

Everything that I can think of is new in the fuel delivery system....could this be the ECU? If so why would the rail pressure drop when it bogs down under load.

I can pull the hp pump and check the screen, but was fairly certain I had most of the crap out of the fuel system when I replaced the pump. I'd rather not pull it if it is not a good chance it is the issue..

Also note, this boat is new to me....I picked it up with 'ethanol issues', and it did have a lot of crap ini the VST and HP pump screen. I've done this repair several times on f115s and f150s.

[99yam40]

Did you measure/monitor the low pressure fuel pressure to see if that meets spec and hold up when high pressure drops?

Maybe monitor HP pump voltage to see if that is changing.

I am not sure if this motor runs the pump through a resister at lower RPM and then straight 12 volts at higher.
Maybe the straight though ground path is s problem if it does. Just a thought

[Landfall]

I have not checked the LP pump output, but it is brand new. Would they bother going through the effort to change the pump voltage with a pressure regulator on the rail? Why not let the pressure regulator handle this?

[99yam40]

You may be correct, but recirculating more fuel at low RPMs could heat it up fuel.
Your motor may run pump on for some times and then off for a while at low RPM. I really do not have the info on that motor and I am not an expert.
HP pump is either running out of fuel to pump, is restricted, or is not turning at the proper RPM for the pressure to drop

So I hope Rodbolt will chime in soon

[rodbolt17]

the HP pump on the F115 runs on 12 V all the time.
sounds like either the pump intake is clogged or the VST is running out of fuel
.
all the vacuum sense line on the regulator is for is acceleration.
it will add about 5 PSI to the rail at rapid acceleration.

[Landfall]

I will pull VST to check. Are these floats prone to go out of adjustment or the needle valves fail? Maybe a glob of that ethanol snot is in the needle seat and obstructing it. It seemed pretty clear when I pulled it but I only blew threw it to check the valve operation

[rodbolt17]

no failure prone stuff.
however that stupid pencil eraser size screen tends to clog easily.

[boscoe99]

.
all the vacuum sense line on the regulator is for is acceleration.
it will add about 5 PSI to the rail at rapid acceleration.

After the engine is no longer accelerating, and is once again operating at a steady higher power, why does the fuel pressure remain at the higher value that was needed for acceleration?

[rodbolt17]

as the throttle plate opens(air valve) manifold pressure increases to about baro pressure.
(vacuum dropped to near 0 "Hg)
with no vacuum to operate the regulator assit it tends to hang out.
at a mid-range throttle setting,especially with a light load, engine vacuum will typically climb back up to the 10-15"Hg range.
the regulator will then lower rail pressure.

at rapid throttle opening several things are happening at once.
1 we just dumped a massive amount of air.
we just increased manifold pressure to about baro pressure.
to compensate the TPS V radically changed and the ECU interpets this rapid change and now not only are the injectors going to fire in sequence they will also fire in groups once per cycle until the RPM requested is met.

now without the additional 5PSI AND the group injection uniform rail pressure would be impossible to maintain.
plus the EXTRA 5 psi,for a given injector ON time, will allow more fuel.

all that ECM is basically is a truth table, also called a map.

as the various sensors feed back a voltage the truth table simply says is sensor X voltage is this then my output to a device is this.
at key on the first thing the ECM sees is a 12V signal on the truth table that controls the main relay,most models, it responds by applying a ground to the main relay to turn it on.
and from there it simply waits,same with when it sees 12v on the cranking wire, it now knows its cranking and decides,based on CPS and CTS and TPS signals how much fuel and ign timing it gets and for how long.

same as the mythical oil pressure system on the F150 and up motors.

its looking at engine RPM AND voltage feedback from the oil pressure sensor.
if both meet its mapped range for that RPM all is well.
to much or to little feed back V for a given RPM and the truth table(map) outputs RPM reduction,visual indicate and audible alarm.

whats funny most sensors that fail are giving readings of over pressure.

which is why you can actually have IN REANGE failures with no codes yet the engine runs stupid.
don't belive me?.
cut in a 2000 ohm resistor in the intake air pressure sensor feedback wire and watch the engine go stupid.
so far I have found the barometric pressure map will accept a range of about 100ft BELOW se*****l to about 22000 ft above.
good luck finding liquid water at 22K ft but the engine is mapped for it.

which is why looking at the laptop screen at key on engine off is always a good idea.

[beachpoint]

f115

Have the same problem as you do. I have had problems before I just did my fuel system over and it still is running good sometimes bad others I am pretty sure it got some junk in the HP fuel pump screen because of the good bad running problems. I was wondering if the pump has a check valve in it. thought if it did not I could backfeed it to see if I could clear it