Pulling my hair out

[Tortuga James]

I have had an issue going on for 6 weeks that is driving me crazy. It started right after I changed my throttle positioning sensor and I changed wheels from a 22 square to a 24x21. The boat runs great for almost exactly 15 gallons, and then takes RPMs away. I have a 6081 John Deere 6 cyl 8.1 liter. I cruise at 2200 rpm and it would take me back to 2000. After that happens, when I push the throttle forward it takes away more until I pull it back to the "sweet spot". After I sat on the dive spot for a couple hours, it would go back to normal for another 15 gallons. It started on the way to Wrightsville in August. I changed every filter on the engine. No effect.

When I got to Morehead, we put a vacuum gauge on the Racor. It would read 6-7 inches on the port side, a little less on the starboard tank. To my mechanic and I it seemed there was a restriction from the racor back to the tanks. We pulled the floats out expecting to find gunk in the tanks. The fuel was sparkling clean. I isolated every hose on the boat pulling from a bucket of fuel. I found two lines to have restrictions. We replaced every line, rebuilt the changeover valves, and the racor filter. The restrictions still remained, so we decided it was the pick ups. We ordered new pick ups, deciding we would have to bend the existing one to get them out (or cut the deck). I didn't have time to install them before I went back down to Wrightsville last week. Still convinced it was the pick ups, and being very frustrated..while I was there I pulled the float out of the port tank and fabricated a temporary pick up to bypass the existing one. I thought that would solve my problem until I could install the permanent pick ups. No change, did exactly the same thing.

Any ideas?

My mechanic refuses to accept any thing other than a fuel restriction. I am not convinced. One noteworthy thing is that it is way worse when I have a heavy load, especially in a following sea. On the way home yesterday with just me she ran great for about 25 gallons, then I could feel fluctuations in the rpms but never really lost them for long and maintained speed.

I am beginning to think it has to have something to do with the electronic throttle control and maybe spinning a larger wheel. But why does she run great for the 1st 15 gallons?

I am freaking pulling my hair out over this.

---------- Post added October 23rd, 2013 at 11:46 AM ----------

7 views but no thoughts? Come on fellas, help a guy out.

 

[Akyla]

Ok James I will take a WAG at it. Don't know a lot about the JD engines other than almost bought a pair in a boat I was looking at and my research then showed them to be pretty good so don't start pulling hair yet.

Electronically controlled, right? Pull the DTC stored in the system and see where that guides you. If the computer is dialing you back due to engine loading, then it will or should show up. Making a change to the over square wheel might have changed the load to the engine and pushing a dive boat loaded with crap is already out there on the load factor. Are you puffing more black smoke than normal, but the computer is good at controlling that. Think about swapping wheel back and see if it goes away. Maybe your 15 gallons is what the computer allows you to use at the higher load rating before it goes into protection mode. Might be time to hunt down a shop that does lots of JD work and beg some advice.

Either way from the looks of the forecast you will have all weekend to work on it!

 

[Tortuga James]

Dave, thanks. I think you are spot on, and I was already thinking the same damn thing. Mechanic only wants to think fuel restriction, but that has been solved. It is time to talk to a John Deere guy.

Thanks for weighing in.... and I worked on remodeling my bathroom all weekend and spent some time off the boat. It was good for my sanity. I have had about enough for this season but I am sure I will be chomping at the bits come April.

 

[briankinley2004]

Can you try running external tanks with new hose, racors, etc directly to engine to completely bypass the existing fuel system? If it ran properly then your mechanic would be correct. If it didn't then you know that's out of the equation. I have found process of elimination works best for me. I know they would have to be more than 15 gallon tanks but perhaps you could fabricate something from a barrel, etc just for a test run

 

[Tortuga James]

Can you try running external tanks with new hose, racors, etc directly to engine to completely bypass the existing fuel system? If it ran properly then your mechanic would be correct. If it didn't then you know that's out of the equation. I have found process of elimination works best for me. I know they would have to be more than 15 gallon tanks but perhaps you could fabricate something from a barrel, etc just for a test run

I thought of that. But with all new fuel lines, and pulling straight from a hose into the tank from the float port I felt like I accomplished the same objective.

 

[Tortuga James]

John Deere specialist coming Monday to plug in the onboard diagnostics computer. My bet now is that it is a low fuel pressure issue at the engine fuel pump.

 

[Tortuga James]

John Deere specialist coming Monday to plug in the onboard diagnostics computer. My bet now is that it is a low fuel pressure issue at the engine fuel pump.

Apparently the new most important tool for a diesel mechanic is not a bag of wrenches, it is a laptop with a wi-fi connection. Apparently Tortuga's engine issue is "paralysis through analysis". Two separate engine sensors (water in fuel and engine speed) were faulty causing the engine control module to dial her back to safe mode. Nothing is wrong with the engine, it just "thought" there was.

 

[Akyla]

Yes the days of a 9/16 wrench and or a hammer solving all your problems is gone. When the new electronic controls engines act up you need to use a lot more thinking to solve the issues. I have a very expensive program on my laptop for diagnosing my cars and it has saved me many times from just tossing parts at the problem. Old engines in the boat still so no need there just yet. Unfortunately most of the marine engines have proprietary software so you have to call them out and pay the price.

Glad you got it figured out. Hope it is warranty...

 

[Tortuga James]

Went back out and ran her after cleaning the engine speed sensor and unplugging the water sensor on the filter. She turned 2460 at WOT and 100% load and made nearly 22 kts against a falling tide. It is a 2400 rpm boat, but I had very little load yesterday. New sensors on order @ $200.

It was out of warranty. 2 hrs travel time at $75, 90 miles at $1.25 and 3 hours on site @ $90. Call it $600 to plug a computer in and track down malfunctioning sensors and a couple of suspect plug connectors on the ECM harness.

I am going with the idea that we didn't replace anything that didn't need replacing. My old style mechanic came to the boat and definitely diagnosed it as a fuel restriction. What pisses me off is that I didn't call Deere in the very beginning. I kept telling the mechanic that it felt electronic, like the boat's governor was kicking in. He wouldn't here it. Lessons learned.