[coves]

Greetings Fellow Boaters!This is the first boat I have actually owned so I have been getting familiar with all its aspects. This is a '96 Mariner 225 EFI with about 280 hours. I am the third owner. Owner number two purshased in 1998 from the original dealer and probably put about only 150 hours on it over that time frame. However, there was never ANY maintenance done on it by the second owner, yikes! So, I have done the basics like lube and lower end oil change, but really nothing more. It starts EVERY time, runs great (I thought), tubed the kids to death on it over this summer, etc, and I added about 45 hours this season. Two issues: At 3000 RPM cruise within 15 to 30 minutes, the "overheat" dummy light and buzzer come on. I can shut down and immeadiately restart and all is normal again. Issue two: the published WOT RPM is around 5600. The best this puppy has done so far is barely 5000, one passenger, low fuel, fully planed and trimmed. Prop is fine, but I figured maybe a slight miss match here but it is the original that came with the engine (stainless, btw, from Merc). Never gave it much thought as all seemed fine, and smooth, etc. Well, yesterday I just happened to pull the cover off to make a general inspection of things and I find that the (facing the back of the engine) top left CDM module connector from the ECM is not even plugged into the module. What the ....? How long has that been disconnected? HOw and why is this? I've been running on only five cylinders? This is totally weird. Well, of course I plugged it back in and went for a ride. Wow! Much better acceleration to plane and I was not even at WOT and I was hitting 5200 RPM! This is too cool. Nothing is ever this easy to fix. Was I ever smug. Well maybe five minutes goes by and I hear and feel and see on the tach a subtle drop of about 500 RPM. DAMN! That was short lived. So now I am lost. Did the disconnected CDM over who knows how long dammage something? Is this associated with the "Overheat" alarm going off? I ran out of time and daylight to explore further, but how all these electronics are interconnected I may be over my head on this one. It continued to run fine the rest of the day and just like it always had, and I did check to be sure the CDM was still connected(it was) and again, crusing at 3000 RPM the "overheat" alarm came on. I stopped and restarted and was back on my way. Never could quite hit 5000 RPM again at WOT. OK gang, what do you think? Whew, thanks in advance for any tips, advice, suggestions, or a beer!Chris

[BW23]

Congrats on troubleshooting the CDM modules. I had to fine a irratic miss above 4500 and ended up changing 3 CDM's in 2 seasons.(97 225 EFI)Your waterpump is probably the overheat problem. But then again I'm not sure why a stop /start would clear the alarm??Wp's still need changed every year or so.

[Reel Precision]

I agree that the overheat problem is due to lack of water. The other I would first start by pulling the plugs off one by one to see if you are hitting on all cylinders. This is the fastest way to find a problem.. If you find a dead cylinder then try and narrow it down by fire, fuel or compression. Fire can be checked with a spark tester or timing light. Fuel can be checked by a number of ways on that efi but start with a pressure test, you may be able to tell just by looking at plugs if it is lean. And of course compression with a compression gauge. Start there and maybe someone on here can help you once you have narrowed it down. If you cant find anything wrong you may over propped but that doesnt sound like it in this case. I dont think you are running all cylinders.

[rodbolt]

hello I have had several that triggered the overheat/oil alarm due to a bad plug wire and the temp wires routed to close to the wire. go to a dealer and buy the CDM module testing booklet. just becase it wont fire does not mean that is the bad one. there are some failures that happen that take out a good CDM its funny but it will. sometimes you replace a non firing one and the new one wont fire either. buy the manual and the test harnesses or take it to a dealer. its a very touchy ECM unit. good luck and keep posting

[coves]

Originally posted by BW23: Congrats on troubleshooting the CDM modules. I had to fine a irratic miss above 4500 and ended up changing 3 CDM's in 2 seasons.(97 225 EFI)Your waterpump is probably the overheat problem. But then again I'm not sure why a stop /start would clear the alarm??Wp's still need changed every year or so.

[coves]

Thanks BW23 for the response! How did you locate the bad CDM's? Spark plug check or did you run the CDM's through the ohm meter test outlined in the Clymer service manual? Thanks again! I may make this a seperate post to the group just to see what everyone else does. Still is tricky stuff, all this electronics!!

[BW23]

I have a OEM Merc manual but did not refer to it.At the dock I used a timing light clipped each spark plug 1 at a time. I would see an "occasional" miss a I rev'ed the motor to 3K rpms. Installed a new CDM then ran the boat up to WOT. They are difficult to troubleshoot because they are erratic from idle to WOT underload.Most mechanics will tell you, start pulling spark plug wires and listen for rpm change.I didn't pull spark plug wires, just clipped my timing light from wire to wire. Be careful at 30mph+ hanging off the back of your boat!!I was not aware of my missing until I tried different props and could not get my WOT rpm's to 5400 or above.If you get it running properly, make a note of your speed at 4K rpm . If that changes in the future, a cyl. is probably missing.