1998 DT140 EFI RPM Problems

[DTAlexander]

I have a 1998 DT140 EFI (2 stroke) with some issues. While operating at about 5000 RPMs, I experienced a sudden drop to about 4300 RPMs. The outboard is on a jet boat so I figured I had sucked something up in the pump. I secured the outboard, trimmed up, found nothing in the pump, so I trimmed down and tried to take off again. When I tried firing it back up it was having difficulty starting. I was able to get it going by dropping the high idle lever and immediately clutching in. I was still only able to get about 4200-4300 RPMs out of it which was not enough to get on plane.

I have done the following:
Replaced Racor filter (it is running on new fuel so I'm not concerned about bad fuel)
Cleaned fuel/water separator
Cleaned in-line filter between VST and High Pressure Fuel Pump
Dismantled Low Pressure Fuel Pump- everything looked great
Checked Fuel Injectors- all looked good as new; all were spraying with good pressure
Changed all 4 spark plugs
Checked spark on plugs- all good
Replaced Fuel Pressure Regulator
Replaced Air Pressure Sensor
Replaced Throttle Valve Sensor
Set idle screw to spec
Tested compression: bottom cylinder was ~135 PSI, top 3 were around 160 PSI. Everything that I have seen suggests 140 PSI should be about normal. Not sure how concerned I should be about the discrepancy, but its definitely on my radar.

After doing all of this I was able to run the outboard at the house on a hose for about 15 minutes with no issue. Put it in the water and once I pushed away from the pier I notice a significant issue with thrust. It was harder than normal to back. I took it out and tried to get it up on plane with no luck. Stuck at 4200 RPMs. The throttle controls reach 4200 at the appropriate spot, but as I push the controls forward to WOT its just not there. She doesn't act labored or anything getting to 4200, she just gets there and doesn't go any higher. When I got back to the pier it was having difficulty at low RPMs and shut down while idling a few times.

I am in a remote area of Alaska with no Suzuki shop nearby. The gauges don't appear to have a "check engine" light so I can't read any faults. Anybody know if there is a light/code reader that I can plug in on this model? I'm running out of options and am starting to seriously consider re-powering. Its a shame though because this outboard is very well maintained and should have a ton of life left in it! Any advice would be GREATLY appreciated!

[briscoe]

The only thing that ran through my mind was the throttle cable. Is it actually moving the throttle lever assembly (stuff). I know you had issues with reverse but it still moves by throttle. I don't know what else could be related. There are others on forum that may suggest something. Good luck brother, you were thorough in you troubleshooting.

[Solarman]

If the cables are fine, then I'd be concerned about the compression difference of the bottom cylinder. As a rule of thumb, 10% is the max difference between any cylinders. So if the bottom cylinder is below 144 psi, it is a concern. The 140 psi is the normal good compression by book, but each motor manufactured starts out with different full compression psi with new rings/cylinders/etc, until they are broken-in, and the rings have seated completely. All of the cylinders at that point have all run evenly, and generally will have similar (within 10%) compression. They should all run the similar compression (within 10%) until something affects one or more cylinders.

Rather than throwing more dollars into it, get a scope to view inside the plug hole of the lower cylinder, to see if a problem exists there?

Best of luck, post back on what you find out .

[DTAlexander]

Thanks for the response. The cables look good. Throttle opens fully at WOT.

I'll definitely start looking into the compression difference. At this point I almost hope that this is the problem. I know its an expensive fix, but at least its a fix! Thanks for the input. I'll keep you posted.

Still very open to other ideas!

[fishingidaho]

General consensus here is broken or cracked reeds, I have a similar issue and will be pulling intake to look at them

[briscoe]

Just pull a plug, not the intake. The good cylinders are excellent comparison to bad. They make an excellent small camera available at H****r Freight. I think it's from Ames. Around $80. Some auto stores have borrow tools also.