1998 df60

[hale448]

I am having a horrible time figuring out a problem with my motor. I can not get it to throttle above 3500rpm. We have tried everything we know what to do to fix the problem but apparently the gremlin is still alive. I was hoping that someone on here has run into this problem, and can share some information.

The motor runs perfect up until it reaches 3500rpm. We have checked all sensors and all that were bad we replaced to include the MAP sensor. We have replaced spark plugs, fuel lines (Even took fuel tank out and cleaned it), throttle cables and steering cables.

From how it is acting I believe it is having a fuel/air problem. Last weekend after replacing the cables, we took out for a test run. We were able to get it up to about 4900rpms, then discovered we had a fuel leak leading into injectors. We came into dock to fix the fuel leak, then took it back out. The 3500 gremlin then showed back up, and we have not got it to run above that rpm.

In short the best we had it running is when we had a gas leak from a hose. I am at a loss as to what is wrong with this dang motor. Can Someone Please Offer Up Any Suggestions. Thanks in advance for taking the time out to read my rather long post, and for any help offered.

[Lunchmoney]

When the fuel supply was reduced due to the leak, it ran better? Have you checked in the silencer for leaves, bee nests, etc? Check out the air flow passages before the throttle body. There's a screen in there that may be clogged preventing adequate air flow. Just a thought.

[hale448]

Yes the motor ran best with a fuel leak. Also checked the screens in throttle body and silencer.

[Moonlighter]

3500 rpm is around the same revs as the neutral throttle limit cuts in. When the engine reaches this rev level, what happens? Does it still sound normal or does it start to break down? If it starts to break down/misfire it could be the neutral switch isnt working properly - either its broken or mis-aligned.

[hale448]

The motor starts to go into a rev limit type mode. Bring rpms back down then runs perfect

[Moonlighter]

The motor starts to go into a rev limit type mode. Bring rpms back down then runs perfect

Ok - then its quite possible you have an issue with the neutral throttle switch on the engine. Located on the linkages. Not hard or expensive to replace. But check its connections first, might simply be a bad wire connection.

Here is the parts list/diagram that may help. If you have the service mnaual you will find it easily enough.
http://www.boats.net/parts/search/Su...NIT/parts.html

[hale448]

Well replaced neutral switch and still having the same issues of not running over 3500 rpm. Does anyone else have any suggestions on what the issue may be.

[hale448]

Ok, took it out on another test run, still same problem so we loosened the fuel line where it comes into the fuel rail with the injectors, and now it is running like a scalded dog. Does anyone have any suggestions as to what we need to check

[redlowrey]

Ok, took it out on another test run, still same problem so we loosened the fuel line where it comes into the fuel rail with the injectors, and now it is running like a scalded dog. Does anyone have any suggestions as to what we need to check

'''''''The pressure regulator sounds like it is stuck closed, not dumping fuel into the vst and you probably have sixty psi instead of thirty six. Stick a pressure gauge on the rail and test it, It is a wonder you didn't see black spark plugs when you removed them.

[hale448]

Well purchased new fuel regulator thinking that would solve the problem. Took the boat out hoping to have solved the problem. Nope! Still have same problem with it not getting over 3500 RPMs. Does anyone else have any suggestions.

[redlowrey]

Why didn't you put a gauge on it first like I suggested, pull the plugs out and see if they are black with soot or a light tan colour and report back the result.

[hale448]

The plugs are brand new. Just put them on. Don't have a gauge to test pressure with so can't put one on it. Thanks.

[redlowrey]

Are the plugs black with soot or are they a tan colour thats what l want to know to see if is running rich

[hale448]

They are the normal black.

[redlowrey]

They are the normal black.

'''''' Normal is not black, they should be a light tan colour, Check the temp sensor voltage with the key on engine hot and exhaust temp, then run the engine and check the map sensor signal voltage, white wire, and report back what you find.