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?

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).

[mitch]

you will need to do a fuel pressure test on your fuel rail may be injectors need cleaning they have a fine filter you can have them cleaned

. does the bulb pump up hard .

i think they are about 50 bucks for a high pressure gauge but for diagnosting fuel problems it is needed.

you should have 42 psi at key on dropping down to 38 psi at idle and under load

[patterson307]

Mitch,

I 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: 37 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.

On a previous sea-trial, I swapped all 4 injectors between the port (bad engine) to the starboard (good engine) and the probelm stayed with the port engine so I think that rulkes out the injectors.

The primer bulb does pump up hard.

Any more thoughts on this one?

Thanks again,
Bruce

[mitch]

sounds like you can rule out the injectors as problem should of gone away

[patterson307]

Mitch,

Thanks for the quick reply. This thing is really starting to get to me!

As I mentioned in the previous post, I did pull the intake and VST and cleaned the filter. It was not dirty at all.

I have not tried to swap vst can with the starboard engine yet, since I didn;t want to mess that much with the "good one:...

Are there any of those sensors on top of the intake (pressure sensor, throttle position sensor, or idle air control) that might be causing this?

On a long shot, I just swithed the ECU brain from port to starboard to rule that out. I always figured that an ECU would either work or not, but maybe they can be more challenging...

I am starting to believe that it must be something either telling the injectors not to open or the spark plugs not to fire. Would a coile dor this? I could swap them from port to starboard also to test this out.

Thanks for your time and suggestions!
patterson307

[mitch]

i am sorry i posted this then relaized what this one was about tried to delete it

[mitch]

i guess you do not have yds it is the only way you can rule out the sensors

[patterson307]

I may be able to hook up a laptop on Monday. I was hoping to get squared away before the weekend.

I just don't fully understand the result of any of these sensors failing, and have yet to hear anyone say that they solved this problem by replacing sensor "x".

If I get the yds on Monday I will check it out and then maybe swap some of the sensors from port to starboard if I have to to identify the culprit so I can get it ordered.

Thanks again!

[mitch]

don,t take off the tps as it needs to be set right ,unless you have the yds to set it at the right voltage

yes it could be a shift switch even, but unless you plug it up you would only be guessing .

yds will not tell you fuel issues but you can run the pump and injectors from it and test spark

[patterson307]

Problem Solved!

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.

[mitch]

That,s great .. just the symptoms where misleading , anyway good luck and great work.

[djbrink1]

I had similar but different problem in that my engine oil light kept coming on over 2000RPM on my Yamaha 115 hp OB and the local shop could not find the problem even on several visits so I took it to Gone Fishing in Dixon and they found the chafed harness. Replaced it and end of problem. I guess the yamahas vibrate a lot at higher RPMs and chafe through the harnesses

[cyrillefrenchy]

if you have two identical engines, try to swap all the components one at the time and test it, it takes a lot of times and patience but it is the only way sometimes to find problems if you have no computer diagnostic test.
i did that several times on waverunners and boats, it always pay off.
sometimes a had to go all the way to the electric harness to find problems. again make sure your fuel delivery is 100 % good.
did you try with a remote gas tank ?and clear tubing on the suction side of the fuel line to track any air leak?