Mercury 225 Optimax Surging

**DieselDood** · 02-03-2024, 11:36 PM

Not my rig, but a good friends.

Last fall I fished with him out of his 2004 Triton with a 225 Optimax. Serial Number 0T946677

He takes meticulous care of this boat. Uses the Mercury Quick Clean and the recommended additives every fill up. Only the "right" Merc oil.

Cold start, it doesn't miss a beat. Even idle for a bit let it get nice and warm like fishing a tourney. Run to the first spot, and give it a hot soak and now it starts to act up a little. The more it's ran and hot soaked the worse it gets.

It takes off doggy, but ... to me this issue feels electrical because how quick and abrupt it can be... it surges in and out. First time it may take off fine then just about half way on pad it will Fall off a little for a second or 2 then all the power is back. Some times it's really quick.

Towards the end of the day, it got bad enough I would have to put my tackle bag by my feet and hop up on the bow, so we could get up on pad.

Once it's on pad, past that... oh 4500 rpm mark, it's fine.

So he brought it to a trusted dealer.
So they are new. No change.

The dealer did get it to act up and said that they didn't see any abnormal readings with the scan tool while driving, other than the coolant temp of one head was low, and that's why it needed Thermostats.

He had another friend go through the air side of things. They replaced the tracker valve and some other parts.
It didn't help.

The tourney I had to get on the front deck to get on pad, I actually had a volt meter in the truck and I ohmed the throttle position sensor, and I did not see any issues. I'd rather do that with an Oscilloscope, but I didn't have one with me at the time.

So, finally to the point.....
He wants me to go through and replace all the rubber components in the fuel system, pull the injectors and air injectors and send them out to get checked.

I'm slightly concerned that, even after doing all that work, we may still have a sensor issue.

My question is this... is there a kit out there for this type of thing OR do I need to sit down on Marine Engine dot com and a spreadsheet and put together my own parts list?

Where would you send the injectors and air injectors to get cleaned and tested?

Thanks guys!
Good/bad thing about it is, after doing all that work, he has a deal on another boat with an ETA of Mid June. Who ever ends up with this rig will be super happy!

**rock** · 02-04-2024, 10:50 AM

Chris Carson on cleaning injectors.

Rock

**XstreamVking** · 02-04-2024, 11:41 AM

Just for the heck of it you might try a portable fuel tank to verify it's not a fuel system issue. Sounds like fuel starvation to me. jm2cts.

**25two.stroke** · 02-04-2024, 04:45 PM

Do a cylinder drop and see if its firing them all. Sounds like one could be dragging. Injector stuck open or fouled plug or both. I see a lot of optimaxes that the thermostats stick open, they run cold, then they foul plugs. Every time I change thermostats in one I also change the plugs even though it is expensive. They do not like to run cold.

If all plugs look good and all cylinders fire then check the air rail for presence of fuel. If there is fuel in the air either an injector is staying open too long or your tracker valve has failed.

If you pass the above two tests I would suspect the tpi. They can look perfect on the DDT but in actuality they are screwed up. And they fail ALL the time. All the time. Surging and lack of holeshot are common symptoms of a bad tpi even if the computer hasn't thrown a code yet. I think I have changed 10 tpis on optis in the last 6 months. Oh and I got a bad batch of them new from Mercury. Ordered 3 and only one was good in that batch. Ordered two more and only one was good lol. Needless to say I did a P&A Warranty return and Merc didn't even question it. They didn't even request the parts back. And when Mercury doesn't ask for them back they already knew there was a problem.

**DieselDood** · 02-04-2024, 08:33 PM

Originally Posted by XstreamVking

Just for the heck of it you might try a portable fuel tank to verify it's not a fuel system issue. Sounds like fuel starvation to me. jm2cts.

I believe he said last season he had all the lines replaced, but that is on my short list of stuff to do if it acts up after we have the injectors gone through.

**DieselDood** · 02-04-2024, 08:38 PM

Originally Posted by 25two.stroke

Do a cylinder drop and see if its firing them all. Sounds like one could be dragging. Injector stuck open or fouled plug or both. I see a lot of optimaxes that the thermostats stick open, they run cold, then they foul plugs. Every time I change thermostats in one I also change the plugs even though it is expensive. They do not like to run cold.

If all plugs look good and all cylinders fire then check the air rail for presence of fuel. If there is fuel in the air either an injector is staying open too long or your tracker valve has failed.

If you pass the above two tests I would suspect the tpi. They can look perfect on the DDT but in actuality they are screwed up. And they fail ALL the time. All the time. Surging and lack of holeshot are common symptoms of a bad tpi even if the computer hasn't thrown a code yet. I think I have changed 10 tpis on optis in the last 6 months. Oh and I got a bad batch of them new from Mercury. Ordered 3 and only one was good in that batch. Ordered two more and only one was good lol. Needless to say I did a P&A Warranty return and Merc didn't even question it. They didn't even request the parts back. And when Mercury doesn't ask for them back they already knew there was a problem.

It's not dropping like a totally dead cylinder. I had another friend that had a plug foul out and that cylinder didn't fire at all and it couldn't get on pad at all.

I'll definitely be throwing plugs in it. I'm that deep into it, it would be silly not to.

The throttle position is what I thought was the issue to begin with. I'll see what he says about getting one to put in it.
Honestly the way it acts, in my years as an Auto technician it feels like the mass air flow sensor is going bad. The low power, pick up, drop, pick up drop, then finally just up and go.

Last fall I believe they put in a tracker valve. When I'm in there I'll still check it out.

It will be nice for whoever ends up buying his boat come June, basically the whole fuel system will have been gone through and trouble free.

**25two.stroke** · 02-06-2024, 02:08 PM

Problem is they have no MAF. They run off the cps, tps and map. Map sensors almost never go bad on those. They do, but rarely. Bad CPS it would never start. TPS is the only one that seems to do what you are saying. Like you said yourself, it seems like the computer doesn't have accurate info to throttle the engine up right.

However...don't rule out a single cylinder issue just because it doesn't sound like it to you. Bad direct injectors will do that too. They will run at some rpms. And if one is sticky and hanging open it causes a cascade effect to other cylinders and to the fuel and air pressures. It isnt like a DFI car. You gotta remember the fuel is injecting THROUGH the air injector. So if one injector is hanging open it can cause contamination of fuel into the air or air into the fuel and pressure surges on the common rail.

**DieselDood** · 02-06-2024, 05:02 PM

Originally Posted by 25two.stroke

Problem is they have no MAF. They run off the cps, tps and map. Map sensors almost never go bad on those. They do, but rarely. Bad CPS it would never start. TPS is the only one that seems to do what you are saying. Like you said yourself, it seems like the computer doesn't have accurate info to throttle the engine up right.

However...don't rule out a single cylinder issue just because it doesn't sound like it to you. Bad direct injectors will do that too. They will run at some rpms. And if one is sticky and hanging open it causes a cascade effect to other cylinders and to the fuel and air pressures. It isnt like a DFI car. You gotta remember the fuel is injecting THROUGH the air injector. So if one injector is hanging open it can cause contamination of fuel into the air or air into the fuel and pressure surges on the common rail.

I'm aware they don't have MAF. I was just trying to give an association to what I'm feeling.

TPS could do it for sure!

Oh I'm not ruling anything out. I've learned by working on my own motors over the years that unless I 110% test it, and even then... it could still be bad.

I had an OMC that had fire on all 6 cylinders. Good spark and everything. I put the timing light on it and all the cylinders AT IDLE were firing when they should. If I brought it up to 1500rpm, suddenly the timing would retard 15*.

I tapped the CDI box with a screwdriver and it would snap to life properly enough that you could tell the motor mounts were bad and the steering had play. LOL

I'm 100% that I'm going to pull the air and fuel injectors and send them off to get cleaned and checked. I hope there is something that comes up that is obvious there and all this is just for knowledge. BUT.... I feel like I'll be doing some digging and proper diagnosis

**XstreamVking** · 02-08-2024, 11:00 AM

You can ohm out the air and fuel injectors to see if there is an electrical problem with them. Might show one is faulty before sending it off.

**DieselDood** · 02-08-2024, 11:02 AM

Originally Posted by XstreamVking

You can ohm out the air and fuel injectors to see if there is an electrical problem with them. Might show one is faulty before sending it off.

True. And I could use a heat gun to "heat soak" them.
I may do the same with the ignition coils too.

**XstreamVking** · 02-08-2024, 11:04 AM

I have sorted out a bad coil by using an ir gun while the engines running. Bad coils get hotter or colder than the others when failing.

**DieselDood** · 02-08-2024, 11:29 AM

If we had soft water, I'd definitely try that! Unfortunately right now we have about 12" of ice, so testing like that may have to wait till after I go through and do everything else.

**DieselDood** · 02-08-2024, 02:17 PM

Am I blind or why can't I find the fuel pressure regulator?
I found the Tracker valve, but not the air pressure regulator or Fuel pressure regulators.

Other than those 2 things, I think I have a pretty good parts list. Please see the attachment and let me know your thoughts

This is the parts film I've been using with the serial number: 0t946677

https://www.marineengine.com/parts/m...D73CD/10125_90