1999 Mercury Optimax 225 wont plane like it should

[mudron08]

To Start:
1. 0G927739
2. 1999/Mercury/Optimax 225 201 Hours
3. 25P Tempest
4. 6150 WOT RPM
5. No Water pressure readings available, do not have a gauge currently
6. No Smart Craft, Have a Diacom system though.


I purchased a 1999 205 Pro DC with a 1999 Optimax 225 in December of 2021. Since it was the middle of winter here in PA I decided to do a bunch of work on it before I started running it alot. I did not test drive the boat when purchased, just ran it on muffs. Once I got it home I added a 6" jack plate because the holes in the transom were a little egged out, so I used Life Calk and bolted the jack plate on. I sent the prop to Mark and had him repair/polish the prop just to make it like new. I took the boat to a mercury dealer and had them go over the engine replacing spark plugs, impeller, air filters, and I had to replace the thermostats and housings because the originals were 120 degrees and needed to change to 130 degree per the service bulletin. I also sent all of the injectors out to be serviced. My hopes in doing all this work was to make sure there were no issues. Fast forward a few months and I got it out on the river and it was having a hard time getting on plane so I lowered the jack plate a quarter inch at a time and eventually it got on plane fairly well but could only reach 5400 rpms WOT. I also started getting alarms and they were for the TPS sensors. The alarms are very sporadic, some days its 4 or 5 times and some days none at all. After some reading I decided to upgrade my battery (thought it was causing the alarms) because it was under spec and the new battery I installed is about 40lbs heavier than the old one. Now I can no longer get on plane. I lowered the engine even further to see if it helped, but it did not make a difference. I also removed the only vent plug and on take off it blew out, so I reinstalled the same plug. So now with the 25p tempest I can only get to 5150 WOT rpm but have to have someone on the bow to take off. I tried a buddies 23P trophy and it gets on plane now with no one up on the bow and my WOT rpm is 5400. I am also still having the TPS alarms. Any information or direction to start looking would be greatly appreciated, sorry for such a long post.

readout1.jpg

readout2.jpg

[Rip Bass]

Check the compression first,then verify spark at each cylinder. It sounds like you may be down a cylinder for some reason. I would also check fuel/air pressure at idle and while you’re trying to plane off.

[mudron08]

I have been wanting to do that for a while now and just have not gotten around to it, I will make it a point to do it this afternoon and post back the results. Thanks for the response.

[mudron08]

Went out to do a compression check this afternoon and my compression tester is missing so went and bought another one and plan on checking it tomorrow.

[EuropeanAM]

Be sure to read the FAQ Section on "Compression Testing".

Check SPARK, check SPARK PLUGS (IZFR5G, gapped at .033").

TPS faults need to be addressed- will need to replace the faulty sensors. This is an obvious problem... address it before looking for something obscure.

Assuming that the first RPM figure you gave was a Type (6150 RPM).

[mudron08]

Getting ready to do a compression check and took the intake cover off to look at the throttle plate. I had my wife push the hot foot to the floor and I still had a lot of room to move the throttle plate. Could this be some of the issue? The only reason I decided to check this was, I have always felt I wasn’t getting full throttle. 7852251F-7A2A-4B70-BE15-9F1F939B71B5.jpegF344E707-5E4B-4772-A3C7-A346BF0DEEC8.jpeg Doing the compression check soon will post back.

[Bryanmc57]

Here's the hotfoot setup tutorial from the FAQ section

http://www.bbcboards.net/showthread.php?t=237541

[mudron08]

Hey Don, would I be able to order those sensors through you? Also I checked the plugs and gaps all within spec and look good. I will snap a picture when I do the compression check. Today has gone as far from plan as possible and I have not gotten that far. That was a typo and was supposed to be 5150.

Thank you Bryanmc57 for the hotfoot setup tutorial, I will check that after the compression check.

[mudron08]

Well checked the compression but I’m not sure how good of a test it was, while I had the engine warming up I had my computer plugged into it and noticed the starboard side warmed up much faster than the port side, I removed the thermostats and both looked good but is that normal? When I shut it down the port side was 90 and starboard was 125. I put them back in and started up again, port side started at 102 and dropped to 93, starboard started at 97 and went to 115 before I shut down. This is in about a minute. The compression and plugs are in picture. 05C3AC0C-CFC7-4C14-8AA7-CC9A358D359C.jpeg

[SilverFox579]

You have a sticking thermostat, suspend both by string in a pot of water using a thermometer to observe water temperature. Note what temperature they reach full open then drop them in cold water, they should fully close within seconds.

Pic is too small to see the plug color.

[EuropeanAM]

+1 on the thermostat problem.

You would need to contact the Parts Department to order parts (see Rhonda's post, pinned at the Top of the Forum).

[mudron08]

Checked the thermostats, seems like the starboard side was slow to open, I replaced it but have not ran the engine again yet. I plan on running later this afternoon. If all goes well I will complete another compression check and report back. If the compression is good, where would I start looking next for something causing it to be down on power?

[EuropeanAM]

Run it and recheck to see if there's actually something to hunt for after this.

[mudron08]

Just a quick update, weather has been crap here so I haven’t been able to pull the boat out to do a compression check but I did pull the compressor strainer and clean it. Hardly anything on it. Just wanted to make sure before starting it back up with a new thermostat that everything was good to go.

[mudron08]

Alright so I completed another compression check with the same results cylinders 1,2,5,6 were 95 and 3,4 were 105. While warming the motor up prior to the test, I noticed again that the port side thermostat reading was low, so I swapped thermostats (starboard has new thermostat) and the problem persisted on the portside, after a few minutes running the starboard was at 144 and the port was 84. At this point I am thinking the Port coolant temp sensor is bad, would this change my air/fuel mixture?

All plugs have about 20-30 hours run time on them and looked the same one side slightly darker than the other.
spark 1.jpgspark 2.jpgengine screenshot1.jpg

[EuropeanAM]

1. Compression tests aren't done with the engine RUNNING- results in Post#15 are substantially different from those provided earlier.

2. Not at all uncommon on this series to see 3 & 4 with elevated compression numbers (within spec, but right on the border of maximum variance).

3. Extremely unlikely that the temp sensor is bad. Simple enough to swap the Port and Starboard sensors to check- but the results you provided indicate that water is leaching past the PORT thermostat in both cases. *

*Make sure you use ONLY the OEM Thermostats, and physically inspect and test them. Have several "new" aftermarket thermostats that are absolutely useless, and even an OEM thermostat can potentially be defective (had one recently that was mal-formed and did not center the valve over the thermister pin properly).

[mudron08]

Hey Don, I went back and checked the picture from my earlier post with the compression numbers and plugs and the results were the same, 1,2,5,6 were all 95 and 3 and 4 were 105. The motor was only running when I was warming it up to temperature, then shut down and completed the compression check. As far as thermostats go I have tried 3 different thermostats in the port side (including the starboard thermostat) and all have had the same results. They are all oem stats. Where would I go from here?

[EuropeanAM]

Is it possible that someone has had the PORT side cylinder head off the engine?

[mudron08]

The original engine was blown up at 10 hours when it was new in 1999 from what I understand. It was replaced under warranty with a new power head back then. It doesn’t seem like the head has been removed. I have only owned the boat for 6 months and I have not.

[EuropeanAM]

There are a very limited number of things that can permit thermostatically-controlled water from dumping through the exhaust. Thermostat, poppet valve, or possibly water jacket diverters that direct the water in a specific path around the cylinders.

Make CERTAIN that the throttle is AT IDLE (zero, not any, not even a smidgeon of throttle) each time the key is turned on, each time the engine is started, and ANYTIME the engine is in NEUTRAL. Any variance from this can cause TPI faults and mal-adapt problems.