F150 Throttle "Feathering" Problem

[patterson307]

This was posted on another site and I did not see a solution.

Yamaha F150 TLRD 2005. Having trouble getting on plane and staying on plane. Motor seems to be bogging and losing RPM. If I feather the throttle from WOT back a little bit then back to WOT the RPMs pick up and it starts too plane out. Once on plane if I keep feathering the throttle I can only get my RPMs to 5000 RPMs. If I leave the throttle wide open on plane without feathering it the RPMs slowly fall and eventually falling off plane. Motor cranks up and starts fine and idles great. I have checked the fuel already and the fuel filters and there doesn?t seem to be any water in the fuel. Any help would be greatly appreciated thank you.
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From patterson307: One of my 2004 Yamaha F150s is doing the exact same thing (with the throttle "feathering"). Has anyone solved this problem yet?

New 2 micron Racors (old ones appeared clean inside).
Cleaned Fuel/Water separator under cowl (was not dirty).
Cleaned VST filter (was not dirty).
New Plugs (were not dirty).

 

[rodbolt]

Re: F150 Throttle "Feathering" Problem

check fuel rail pressure at the problem RPM and load.
ditch the 2 micron filter use a 10 micron with a 90 GPH flow rating.
remember each injector also has a screen.

 

[patterson307]

Re: F150 Throttle "Feathering" Problem

Rodbolt, Thank you very much for the prompt reply.

Since I don't yet have the means to check the fuel rail pressure under load, I just switched all four injectors from the Port (Bad Engine) to the Starboard (Good Engine) to see if the problem would switch sides.

This evening I sea trialed the boat and there was no difference, the problem stayed on the Port side.

I have also run the Port engine on an external fuel tank to try to rule out fuel tank pickup and check valve problems. No change.

The good engine also has the 2 micron Racor so i will rule that out for now, but take your advice to switch back to the 10 micron Racors in the near future.

I am beginning to suspect the electrical fuel pump that sits inside the VST cannister. This part is close to $400.00, but I recently had to replace the electrical fuel pump on my Ford F-150 so I guess that they can go bad.

My pair of Yamaha 2004 F-150s only have 200 hours on them and they were put into service in the Spring of 2004.

Would you recommend buying the fuel pump or are there some of the pressure regulators that might have gone bad? It looks like there is a vauum actuated regulator attached to the VST and an electrically actuated pressure sensor on top of the intake.

Thanks again,
Bruce

 

[99yam40]

Re: F150 Throttle "Feathering" Problem

swapping parts will not tell you about the filters/screens . like Rodbolts said check the pressures or replace the internal filters/screens

 

[patterson307]

Re: F150 Throttle "Feathering" Problem

Rodbolt,

I finally bought a fuel pressure gage and sea-trialed again to measure the rail pressure at the problem RPM and load.

The Fuel Rail Pressures were as follows:
Key on, Engine not running: 40 psi
Engine idling: 35 psi
Engine under load at any RPMs: 40-42 psi

Engine idles smoothly and runs smoothly up to a little over 2,000 RPM and then stumbles and won't gain any more RPMs. If you "pump" the throttle control repeatedly it may surge 2,000 RPMs. When this surge happens, the fuel rail pressure does not change.

Any more thoughts on this one?

Thanks again,
Bruce

 

[rodbolt]

Re: F150 Throttle "Feathering" Problem

when you"pump" the throttle the TPS value changes rapidly.
the ECU intererpets this as rapid acceleration and the fuel pressure regulator loses vacum and spikes the rail pressure about 5 PSI.
the ECU opens the pulse width(injector on time) and also fires the injectors simultaneously.
this acts like an accelerator pump giving the engine more fuel for rapid acceleration.
sounds like clogged injectors.

 

[patterson307]

Re: F150 Throttle "Feathering" Problem

After a lot of fuel system diagnostics, my problem turned out to be electrical.

To reiterate the 2004 F150TXRC symptoms and some of what was done:

Engine idled smoothly and ran smoothly up to a little over 2,000 RPM and then stumbles and won't gain any more RPMs. If you "pump" the throttle control repeatedly it may surge 2,000 RPMs. When this surge happens, the fuel rail pressure does not change.

Previously I had tried the following:
Replaced fuel primer bulb.
Inspected check valve in gas tank.
New 2 micron Racors (old ones appeared clean inside).
Cleaned Fuel/Water separator under cowl (was not dirty).
Cleaned VST filter (was not dirty).
Cleaned "F" filter (was not dirty).
New Spark Plugs (were not dirty).
Swapped all 4 injectors between the port (bad engine) to the starboard (good engine) and the problem stayed with the port engine.
Swapped ECUs between the port (bad engine) to the starboard (good engine) and the problem stayed with the port engine.
Checked fuel rail pressures:
Key on, Engine not running: 40 psi
Engine idling: 37 psi
Engine under load at any RPMs: 40-42 psi

I checked the fuel hose routing under the cowl and noticed a wiring harness laying on top of the shift rod lever. The shift rod had worn through the insulation on the wiring harness bundle and worn through the insulation on the light green and pink wires in the bundle. When I relocated the wiring harness the engine ran perfectly!

I think that one of the wires (maybe the pink one was going to ground and sending a false Thermo-switch signal to the ECU and the fuel injection for cylinders 1,3, and 4 was being cut off above 2,000 RPMs.

Attached are 3 pictures that show the bad wire and the service manual pages that refer to the injection being shutoff due to 1 of 4 possible conditions.

I hope that this helps others that have been experiencing these same symptoms.

 

[BaileysBoat]

Re: F150 Throttle "Feathering" Problem

Great post. Shows the value of a factory manual.

 

[rodbolt]

Re: F150 Throttle "Feathering" Problem

engine was rigged incorrectly,double check the other.
double check your alarm horn and the visual indicates.
when the pink wire grounded you should have had an audible and a visual indicate.
you should have been blowing fuses for power trim as well.
however i dont think that was your issue as the system when it goes into RPM reduction wont go over 2000 RPM and it misses like crazy.
however if you had something shorting to ground enough to drop system voltage you lose ign and fuel.
with that pink wire shorted to ground you simply wont hit 5000 RPM AND the audible alarm sounds,if its there and operable.
you may wish to test it.
also IF rigged correctly with the proper yamaha keyswitch,if you short the pink wire to ground it takes both engines down to 2000 RPM.
does this for low battery voltage,overtemp and low oil pressure.
none of this was mentioned so if I were you I would carefully inspect my rigging before you have issues again.