2001 F115 surging throttle

[fishon195]

Last three outings motor showed poor inconsistent surging throttle after adding fuel system cleaner, mostly at higher rpms.
Also poor starting issues.
Ran two tanks of premium fuel to run out contamination
Replaced plugs fuel filters . my suspects are cracked fuel pickup in tank which has happened before, VST clogged with varnish.
still running poorly.
computer check? or waste of time?

[99yam40]

seems monitoring fuel pressures would guide you to a lack of fuel , plugged up VST, or cracked pick up if that was a problem
computer will help eliminate a lot of stuff

[TownsendsFJR1300]

I would drain the VST and catch what comes out. Should give you an idea of what's in there...

Running off an independent, portable tank would rule in or out the main tank...

I gather your running Ethanol fuel with NO stabilizer? Has the fuel sat for awhile?

[walleye1]

Have your injectors cleaned after you clean the fuel system.

[rodbolt17]

why bother with snake oil?
why bother with 93 octane when it is designed for 87?
monitor the rail pressure.
90% of the time it is VST/injectors.
for what you have spent on snake oil and premium you could have done the fuel system.

[fishon195]

I gonna go with Rod who helped me out awesome a few years back with a voltage drop problem ended up being the rectifier.

Before reading this I ran double Sea Foam thru the fuel tank. problem seems greatly improved but not completely.
i may have to take off the VST and clean it out, . is there a gasket key to replace it or just goes back.
Ive done it before maybe 5-6 years back. i remember left the harness connected and just folded back the intake tubes.

Would any kind of a bad sensor signal cause this? had another problem where I could not start boat after it was warmed up .
ended up being throttle position sensor after tech put on computer..

[pstephens46]

I gonna go with Rod who helped me out awesome a few years back with a voltage drop problem ended up being the rectifier.

Before reading this I ran double Sea Foam thru the fuel tank. problem seems greatly improved but not completely.
i may have to take off the VST and clean it out, . is there a gasket key to replace it or just goes back.
Ive done it before maybe 5-6 years back. i remember left the harness connected and just folded back the intake tubes.

Would any kind of a bad sensor signal cause this? had another problem where I could not start boat after it was warmed up .
ended up being throttle position sensor after tech put on computer..

VST has a goofy gasket I believe similar to F150. Buy one. It is delicate and gets cruddy. Hard to clean without stretching it.

[fishon195]

Spent 4 hours on the water today, by the way engine is a 2001 F115TXRZ saw some unique symptoms,
throttle started out sloppy but after 15 mins or so stabilized except for the RPM range from 3900-4400.
Throttle was consistent and settled in very stabile outside this screwy rpm range, it was fine all the way from 800 to 3900 and 4500 to 5200, WTF?.

As soon as i hit 3900 it starts to shutter and surge back and forth but as soon as hit that 44 threshold it settles down all the way up to 5200.
So i disconnect the Shift position sensor (don't ask me why), no change from shutoff to max throttle. same symptoms except idle throttle was slightly higher 800-900rpm.

Does the computer need the signal from the SPS to keep a stable throttle?
What happens with the engine throttle body at this 3900 rpm?
Do i still really need to get into the VST?.

Sorry for all these questions but .. I'm just trying to think.....
I have to assume that the VST does not know what my throttle is doing if it has a debris in it, it should **** up anywhere not just this RPM range.
Fuel pressure has to be correct and injectors clear to run consistent rpm at 5200.

[99yam40]

Unless you verify things ,you cannot be certain what is in spec and what is not. guessing causes problems when troubleshooting.
your use of the word throttle seems kind of strange to me "sloppy throttle, Throttle was consistent, idle throttle, stable throttle"

clean the fuel system if you had or have fuel problems

[fishon195]

Idle throttle = idle speed, sloppy throttle = poor engine response to acceleration,
Throttle in my sense means the "engine running SPEED" or RPMs.
Fuel was stabilized with Seafoam before non use. Older gas used up completely. Camera in tank shows clean internals
I don't think I can have a fuel problem if it runs perfectly fine at wide open throttle and slow speeds.
Maybe a fuel line????

[TownsendsFJR1300]

Guess you won't at least drain the VST (one screw) and examine what comes out... ?

[walleye1]

Sea foam is not a fuel stabilizer it is a cleaner no matter what it says on the can. And you are adding more alcohol to ethanol.

[99yam40]

Sea foam is not a fuel stabilizer it is a cleaner no matter what it says on the can. And you are adding more alcohol to ethanol.

Does sea foam have ethanol in it?
I did not think it did, but have not looked at a can in some time

[pstephens46]

Need to start over. Post 2. Plug whatever sensor back in to wiring. One step at a time.

[fishon195]

Need to start over. Post 2. Plug whatever sensor back in to wiring. One step at a time.

Not sure what you mean did not unplug anything …….yet oh yes sorry just the SPS but that did not do much.