2000 DF40 Missing under a load

[Florida Fisherman]

Hey everyone, I'm having issues with my 2000 Df40 and wanted to pick your brains. The motor is missing when going forward (2000 and up RPM range) and will shut off, but if i put it in reverse it will run up to 3500 rpm with no hesitation, it also idles perfect. Today was the first time I thought to check reverse even though I have been chasing this issue for a good while now.I thought it to be a fuel issue, I have replaced the topside gas tank, fuel line and connectors including primer bulb, spark plugs, and today i replaced the low pressure fuel pump. I'm beginning to think it could be an electrical issue maybe a sensor somewhere. It has me stumped at this point so thanks in advance for any input or advice.

[Moonlighter]

Can you be a little more specific about what the engine is doing? First, you said it is missing, which is typically when the engine runs but has a misfire on one or more cylinders, but then you you say it shuts down?? Does that mean that it get to 2000rpm and completely stop running?

These could be two quite different issues so it would help to be clear on what is actually happening.

One thing that springs to mind is the neutral throttle switch on the engine, that prevents the engine over-revving in neutral. It cuts in about 2000-3000rpm depending on the engine model. In neutral, if you rev beyond this range, the spark is interrupted, fuel supply restricted, and the engine will madly stumble until you back off. If it is not operating correctly and is still activated when the engine is in forward gear, it may even result in the engine cutting out. So it might be an adjustment issue, or a faulty switch. Fairly cheap part and not hard to replace, so I gather.

[Florida Fisherman]

The motor will drop rpm and rev back up, acting like it's running out of fuel while moving forward , and as of today started cutting off. I can watch the tach and the needle will bounce just a little, that's when the sputtering and bucking begins. It use to run up too 3000 RPM before acting up, but the problem has gradually gotten worse to the point now it will start acting up at 2000 RPM. What you describe about the neutral switch sounds a lot like my problem, is there a way to ohm out this sensor to check and see if it's working?

[redlowrey]

Sounds like a fuel problem, check and make sure the vst is getting plenty of fuel from the low pressure fuel pump, and if it is pull the vst down check the filter screen inside.

[artdf175]

After you are sure it is not fuel-- check the wiring
What you describe is similar to what I experienced when a connection /splice in the white wire corroded
I had intermittent power failures when running Because this wire is also the power to the dash instruments they flickered and the GPS would go out and have to be started over
When there is a power loss in this wire, the power the engine control module is lost and the engine cuts out
Finally the connection failed completely
Art

[Florida Fisherman]

Hey guys sorry for just getting back to yall, I ended up having to put my boat in the shop. The problem ended up being a fouled VST tank, had to replace the whole thing, the mechanic said it was full of rust and varnish from the ethanol in our gas here in North Florida. Its still in the shop as i'm having them go through the entire motor to make sure everything else is up to par. Thanks for all the input fellas.