2003 Mercury 250EFI won't go above 2k RPMs.

[LIGlastron]

So the story is I went to take the boat out and I'm only running 2000 RPMs Max but as it goes on it sounds as if I'm running out of fuel. I have checked everything as far as the basics. All fuel pressure is in spec. The ignition is inspect no field coils brand new plugs. I even replace the high pressure fuel pump thinking it was that due to the symptoms as well as the low pressure diaphragm pump. But as said fuel pressure is inspect so it doesn't seem to be that. Also fuel injectors were pulled and flow tested and that was brand new. Compression is 130 across the board. Really stumped at this point seems almost electrical related. TPS map sensor spark plug wires are all almost brand new. Anyone have any ideas?

The day before I took the boat out I changed batteries to new batteries and I change the propeller from a 27 to a 24 pitch due to feeling like I had a lot of prop slip. I tested the batteries with the legitimate battery tester and they tested okay. I'm almost left with nothing to do but put the original prop back on and the old batteries and just see what happened since that's all that was changed.

[Merc 2.5]

Did u try the primer bulb?

[LIGlastron]

Well the bulb stays firm and it isn't too old, also fuel pressure was tested with gauge throughout the rev range in the water. Stayed within spec.

[LIGlastron]

Did u try the primer bulb?

Well the bulb stays firm and it isn't too old, also fuel pressure was tested with gauge throughout the rev range in the water. Stayed within spec.

[flabum1017]

Could be the high side of the stator dropping out....

[LIGlastron]

Could be the high side of the stator dropping out....

I was told this engine has a trigger and no stator could that be correct?

[LIGlastron]

Just to say what was addressed. New spark plug wires,new spark plugs, new high pressure fuel pump, rebuilt the low pressure diaphragm fuel pump, check all coils for a spark during load test in the water all checked okay. Fuel pressure checked okay throughout the range even when starting to bog and at 2K RPMs. TPS seem to check okay. .38 at idle, and 4.96 at wide open. Anyone have any input? this point you could tell I'm just pretty much throwing parts at this thing. Do TPS and map sensor rigzone about 2 months ago and boat was running great after. seem to change the two batteries to a GM's and change the prop and now this is my problem

[flabum1017]

I was told this engine has a trigger and no stator could that be correct?


Oops, you're right.

I assume you have checked for good spark on all cylinders?

[flabum1017]

Is your alarm working? does it beep when you turn your key on?

[LIGlastron]

Is your alarm working? does it beep when you turn your key on?
good spark on all cylinders with checked with diagnostics on the water we went through all the basics nothing seems to be wrong. I am getting a single beep when I start the key. One thing I did notice the last time when I was acting up was for a short time I was getting one long beep followed by one short additional beep but then it just stopped happening so I'm not sure what that was about. Since then it's been doing the normal one beep per start and diagnostically everything seems okay

[half fast]

What plugs ? Should be QL77CC champions . Believe that motor has a stator . It also has a key way between the flywheel and crankshaft . Make sure it hasn’t sheared . Hf...

[LIGlastron]

What plugs ? Should be QL77CC champions . Believe that motor has a stator . It also has a key way between the flywheel and crankshaft . Make sure it hasn’t sheared . Hf...

Yes I'm running QLC77çcs at .035 .

I'll read into the stator more, been going through all possible options.

As far as the keyway wouldn't that make it rev up uncontrollably? Is the only way of inspection on that looking behind the Reed cages?

[RSWORDS]

If you have the single ecm on the side you dont have a stator.

Sounding like your going into limp.

The alarm should be sounding though.

I just had this happen to my 3 liter last weekend, port temp sensor went bad.

It could be alot of other things though. A computer would help.

[LIGlastron]

If you have the single ecm on the side you dont have a stator.

Sounding like your going into limp.

The alarm should be sounding though.

I just had this happen to my 3 liter last weekend, port temp sensor went bad.

It could be alot of other things though. A computer would help.

I went to a Mercury repair shop yesterday as a last resort after throwing way too many parts and money at the thing. Of course he didn't find the problem however it gave me more confidence in the motors health. we did both bench test and water tests with the diagnostic equipment hooked up to the engine:

-Great compression, 130 straight across the board cold engine.

-Ignition system all working properly even with load. he dropped off one cylinder at a time with the DDT.

-Good fuel pressure at idle and under full throttle pressure is not dropping off when issue is occurring

-Removed injectors yesterday and bench tested them. The spray throughout all 6 looked brand new. Perfect flow.

-Reed valves and cages all perfect

-Voltages seem good.

-TPS seem to check okay. .38 at idle, and 4.96 at wide open

He checked everything that he could with his knowledge of two stroke efi engines. He was a very thourough tech and went further than expected with it. He deals with more for strokes nowadays. However he hooked up diagnostics to the motor no codes, no warning lights. It does have the single ECM. Would the temp sensors throw codes? I have a certified Merc manual for my engine so I know how to test those sensors. What about weak oil pump, would that restrict me to 2k? Wouldn't there be warning sounds? What can I possibly look for that could keep guardian system from activating ?

Could it be the ECM? Really the only sensors that haven't been changed practically are crank position sensor, temp sensors, thermostats, and poppet valve.


There's very little left on this engine that's old after all the parts I've thrown at it. At least I'll know most of the parts on it are new ��

[Merc 2.5]

If temp sensor is bad it will read cold and pour the fuel to it I believe, b worth testing if u can

[LIGlastron]

If temp sensor is bad it will read cold and pour the fuel to it I believe, b worth testing if u can

so what you're saying is it might be running super rich from the sensor irregularity that's bogging the motor down?

[Merc 2.5]

so what you're saying is it might be running super rich from the sensor irregularity that's bogging the motor down?

Yes possibly , I'm not a efi guy. but I've seen plenty people have that issue , be kinda like runnin it with choke on all time

[LIGlastron]

Yeah it seems super rich like when I punch it to the floor it just goes Max 2K RPMs and then sounds like I'm losing fuel which would make sense if it was just way too much fuel. Going to test that temperature sensor and go from there thanks so much

[Judge85]

I’m the tech who was helping out on this problem. No faults for temp or oil pump
(it primes and runs on demand with laptop), 100% power available, shift switch registers in gear while underway at 2,000 rpms when engine won’t progress any further. Port and starboard temp sensors reading while underway (150-160). Map sensor values and tps are good at idle and wot. Cylinder misfire test at 2,000 - all coils responded, fuel pressure rock hard at 40psi, fuel injectors flowed perfect on the bench....it just won’t budge off 2,000 like it’s being limited but no guardian active and laptop shows 100% power available with correct spark advance.....very strange....I rarely get stumped, and this ones got me scratching my head. Thanks in advance to anyone willing to give helpful advice as we’ve gone through what seems like everything . I haven’t seen one of these ECMs go bad but I’m thinking it’s a possibility.

[RSWORDS]

If temp sensor is bad it will read cold and pour the fuel to it I believe, b worth testing if u can

Not always. Mine was overheating as soon. As it started. Computer showed 192* on port head after sitting all night. Lol

[RSWORDS]

I’m the tech who was helping out on this problem. No faults for temp or oil pump
(it primes and runs on demand with laptop), 100% power available, shift switch registers in gear while underway at 2,000 rpms when engine won’t progress any further. Port and starboard temp sensors reading while underway (150-160). Map sensor values and tps are good at idle and wot. Cylinder misfire test at 2,000 - all coils responded, fuel pressure rock hard at 40psi, fuel injectors flowed perfect on the bench....it just won’t budge off 2,000 like it’s being limited but no guardian active and laptop shows 100% power available with correct spark advance.....very strange....I rarely get stumped, and this ones got me scratching my head. Thanks in advance to anyone willing to give helpful advice as we’ve gone through what seems like everything . I haven’t seen one of these ECMs go bad but I’m thinking it’s a possibility.

that is a chi scratcher. Aren't they fun?!

Any access to a known good ecm?

Gearcase ok?

[LIGlastron]

that is a chi scratcher. Aren't they fun?!

Any access to a known good ecm?

Gearcase ok?

No access to good ECM at the moment
Gearcase was working properly and recently changed with new fluid. Was a little milky but was not giving any issues.

[Merc 2.5]

Not always. Mine was overheating as soon. As it started. Computer showed 192* on port head after sitting all night. Lol

10 4. Ya I'm not efi guy. I just member it being a prob for some. so I said that so he could test it. Prob far fetched. yall the 3.0 guru. I was just holdin him over haha

[half fast]

Take a look at look at the cylinder walls , we had two different 3 liters with the sleeves turned and it gave us fits . Bring #1 cylinder to top dead center and check flywheel is at 0 degrees . Hf...

[LIGlastron]

Take a look at look at the cylinder walls , we had two different 3 liters with the sleeves turned and it gave us fits . Bring #1 cylinder to top dead center and check flywheel is at 0 degrees . Hf...

What's the best way to visually inspect this?

also last night looking or into the sensors and electrical I did look closely at the map sensor and it did look like it could have been slightly clogged with a bubble of oil. Would this cause these symptoms? I had just replace map sensor about a month ago so I didn't look too much into it

[Merc 2.5]

Half fast really knows tons bout these motors , with that said was it a oem sensor or aftermarket off ebay? Aftermarket stuff has tendency to go out quick or even bad out of the box sumtimes.

[LIGlastron]

So last night I did a lot of electrical testing on the motor and some ohm readings on sensors etc. Map sensor tested faulty so I replaced it with a good one I had. Other than that didn't find anything so I thought for sure the map had to be it. I threw the hydromotive props back on the 24 pitch and went on the water. Seem to have slightly better punch off the start but still same 2,000 RPM issue. I brought the original 27 pitch prop with me as a last resort. went back to the dock swap to the 27 pitch and the boat was able to rev up and get on plane just like it used to but still only getting 4800 RPMs out of it. All of this and it was just the original propeller swap I had changed. I feel so dumb but like I said I'm not getting full RPM out of the problem and it feels like it's getting cavitation and slipping. Do I need the 24 pitch drills for avs??

[LIGlastron]

So last night I did a lot of electrical testing on the motor and some ohm readings on sensors etc. Map sensor tested faulty so I replaced it with a good one I had. Other than that didn't find anything so I thought for sure the map had to be it. I threw the hydromotive props back on the 24 pitch and went on the water. Seem to have slightly better punch off the start but still same 2,000 RPM issue. I brought the original 27 pitch prop with me as a last resort. went back to the dock swap to the 27 pitch and the boat was able to rev up and get on plane just like it used to but still only getting 4800 RPMs out of it. All of this and it was just the original propeller swap I had changed. I feel so dumb but like I said I'm not getting full RPM out of the problem and it feels like it's getting cavitation and slipping. Do I need the 24 pitch drills for avs??

[Merc 2.5]

Try a completely different prop in 24 if possible , what's ur prop to pad #

[LIGlastron]

I spoke with them over at hydromotive and they're going to drill the prop with some one inch vent holes. When I bought the prop he said if I feel like it has too much bite that they could drill them for me but what I thought they meant by that is just way too much bow lift and feeling like it is gripping too much I did not think of it not being able to spin the prop past 2000 RPM's it totally felt like a fuel or ignition issue!! How embarrassing!!!

As of right now I'm getting Max of 4900 RPMs and 46 miles per hour. I know this boat is heavy but other accounts of LS7 boats with 200 to 250 outboards doing high 50s to mid-60s. Hoping the extra thousand RPMs will get me there.


I had ran a two-by-four along the bottom of the pad and it is even with the top edge of the propellers hub or around 2" above center of prop shaft give or take.

That's another thing that I am looking into is if the height is maybe too low and is also contributing to the terrible takeoffs. I am considering a Jack plate but with the 30.5" set back from the stainless marine gill bracket I didn't know if that was too much set back already to add another few inches for the plate. What do people think about this?

By the way thank you everyone for all your input and advice there's nothing more valuable than hearing from people's experiences and first-hand reports!! Going to be flying on the bay soon!

[LIGlastron]

Try a completely different prop in 24 if possible , what's ur prop to pad #

I meant to tag you in the post above to hear your input on the numbers. I'm really wondering if the height of the Gill bracket is right given I'm not sure who originally rigged this boat

[Merc 2.5]

Im not familiar with ur rig , others r more qualified than me for sure. If your prop shaft is roughly 2in below pad then ur pretty close and not horribly deep , so I dont see that being a issue at the moment

[Zoomba]

So the story is I went to take the boat out and I'm only running 2000 RPMs Max but as it goes on it sounds as if I'm running out of fuel. I have checked everything as far as the basics. All fuel pressure is in spec. The ignition is inspect no field coils brand new plugs. I even replace the high pressure fuel pump thinking it was that due to the symptoms as well as the low pressure diaphragm pump. But as said fuel pressure is inspect so it doesn't seem to be that. Also fuel injectors were pulled and flow tested and that was brand new. Compression is 130 across the board. Really stumped at this point seems almost electrical related. TPS map sensor spark plug wires are all almost brand new. Anyone have any ideas?

The day before I took the boat out I changed batteries to new batteries and I change the propeller from a 27 to a 24 pitch due to feeling like I had a lot of prop slip. I tested the batteries with the legitimate battery tester and they tested okay. I'm almost left with nothing to do but put the original prop back on and the old batteries and just see what happened since that's all that was changed.


I had a 3.0 225 carb with similar problems. Pissed me off to no end for months and stumped the guy I bought it from.. It ended up being a burned ground pin on the # 3 cdm coil pack connector. Unplug and inspect each pin on each cdm connector. I found it by marking tdc and cylinder # on each cylinder on the flywheel, then making sure each cylinder was firing at tdc, with a timing light, move the timing light pickup to each cylinder plug wire one at a time. (This is called " indexing the flywheel", allows you to check each cylinder's timing) At about 2000 rpms, the timing mark started jumping around a bunch visibly, causing the problem on cylinder 3, which affected all the other cylinder's timing. The female portion of pin connector was clearly burned once I really looked. Crimped on a new connector and off to the races!! It could also be a chafed CDM wiring harness. Good Luck.

[Merc 2.5]

You havin any luck with ur motor?