DF 225 OverRev Problem

[Wired Up]

Bought 2 new DF 225s back in 2004 for my Mako 282, real anal about maintenance, and only had 1 problem which seems like a miracle for outboard engines, until last Saturday while spending a nice day in the wild blue water off Sebastian Inlet I experienced my second major problem.

Problem:

The week before I changed the oil, filters, lower unit oil, and water pumps, which I have done 6 times with no problem, this seemed to be a clue.
When trying to go over 4K RPM the port engine backs off to 3K which is the symptom. Motor ran fine all day, like it normally does, purrs like a kitten. While in the river heading to the ramp I leaned into the throttles and again the same problem. In the service manual under the section "Overheat Caution" it describes the problem exactly what I have, by the way the service manual is great. So no overheat problem all day (10 hours of running and trolling). In the section "Water Cooling System" I followed Suzuki's List: Pulled out the lower unit and double checked the water pump and impeller, check the water tube, pulled both thermostats (which I changed 2 years ago) and tried to check the water pressure valve, but it was "living in there" and broke to pieces when yanked out, since I have ordered 2 more covers, 2 pressure valves and 2 O-rings. Highly recommend you double check this on Suzukis, after 10 years the corrosion was bad, really bad. The next 2 items were cylinder head and block which with the way the engine behaves doesn't fit the bill. Swapped cylinder sensor and both exhaust manifold sensors, still had problem, I don't like to do it, but put engine in gear and cranked it up, around 4200-4400 RPM the "over rev" LED lights and engine backs off. I finally ordered the diagnostic kit on E-Bay, as I have never needed to reach so deep. Knowing the wonderful world of outboard electronics it is probably the EMC!

So if anybody has experienced a similar problem I would love to hear from you! Thanks for listening to my babbling...

Capt. Mike

[keakar]

definitely cant find reason to doubt your thoughts on everything so far but also contemplate if corrosion has made a breach from the exhaust to the water jacket then exhaust pressure will prevent the water from flowing at faster speeds and effectively cancel out waterflow. this would be visually checked if you notice a drop or stoppage of water from the tattle tail.

I have a 2002 DF40 that just had a corrosion hole breach the head and I take very good care of it and flush it well and it had less then 300 hours so I would suspect whatever you find to be the problem on a motor that old is highly likely to be a corrosion related issue, maybe even a blockage in the heads water passages which would give no other indication other then just overheating at higher revs but cooling fine at idle or low speeds

[Wired Up]

Thanks for insight!

Good thought, I have fought corrosion problems since beginning with the engines, down to the stupid clips they use for hose connections.

[Wired Up]

Overrev - Problem finally Fixed!

Reading the service manual correctly really helps and also have a second engine on the back of the Mako makes troubleshooting somewhat easier.

The "Caution System" which I posted was incorrect; the condition had nothing to do with overheating. On page 3-35 of the DF 255 service manual the table outlines that with "no buzzer" it is a pure "over-rev" condition. so if in the technical field you know what "RFM" means...

I received the Diagnostic SW and Cable bought via E-bay and received it within 2 weeks. I would highly, highly recommend if you own a laptop and these big blocks (supports any engine) you buy this for $125, its a steal and vital for monitoring system service data along with ability to troubleshoot issues with your Suzuki engine, and the DVD contains all the service manuals for all engines!. Upon loading SW the only problem I had was getting the driver to load as the cable is a RS-232 serial interface to the engine (9600-1-N) to the laptop USB interface requiring to address COM-1 and only that particular port configuration.

The first thing that caught my attention was the Diag said the engine was in "Forward" and I was in neutral! this lead me directing to the "Shift Position Sensor" and upon removing it and using a VOM I saw the resistance was "flaky" and not linear, basically a spring loaded potentiometer. I then ordered a sensor from Boat.net. Also the order included anodes (7 per engine), along with pressure valves and new plates. The anodes after 10 years looked like little round "salt licks", and I flush the hell out of these engines. The clutch assemble and throttle parts, like bushings, were wore and other parts corroded, this is my port engine so maybe being in the center of the transom more water intrusion as the starboard was not bad, but still took it apart and cleaned and greased.

When receiving the SPS and reconstructing and refurbishing the clutch and throttle assembly (cleaning, painting and greasing) once installed and observing the diagnostics SW I aligned and was able to test the shift mechanism via the software. Then testing my original condition, thinking that the engine thought it was in neutral and upon throttling up when into the "over-rev" condition, but no luck, still had my problem, damn.

Going back to the diag SW everything looked fine, my first suspicion, was maybe the Throttle Body Assembly but seeing the voltage and opening specs, while checking other engine, looked good. next swapped the MAP and that didn't help, then the CKP (which were out of spec supposed to be .75mm next to flywheel, and they were corroded), then CMP, the shotgun was in motion.

Finally, I looked at the service manual schematic diagram and logic and realized that the tach reports to the ECM as it is reporting the RPMs to this logic, duh! Upon swapping the tachs I realized my thinking was correct and it fixed the problem! I must admit I did go back and forth twice to ease my mind on the problem.

Sorry to be long winded, but posting this may help some poor soul, interesting enough the starboard tach went bad years ago as it was not reporting service hours on power up, maybe the digital ones would be better!?!? They are made by Faria (US), not Japanese.

Tight lines,
Capt. Mike Oyler
moyler43@gmail.com

[keakar]

glad you got it all sorted out and with your history of corrosion you should unplug the main wiring harness and smear a little grease in there on both motors as well as any other plug connections so you can avoid corroded wire connections

also don't forget the tach connections under the dash, they are famous for getting corroded after a few years