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

**LIGlastron** · 06-07-2020, 08:32 AM

Originally Posted by 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

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** · 06-07-2020, 08:47 AM

Originally Posted by LIGlastron

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** · 06-07-2020, 08:56 AM

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** · 06-07-2020, 09:27 AM

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** · 06-07-2020, 10:32 AM

Originally Posted by 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

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

**RSWORDS** · 06-07-2020, 10:34 AM

Originally Posted by 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.

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

Any access to a known good ecm?

Gearcase ok?

**LIGlastron** · 06-07-2020, 11:37 AM

Originally Posted by RSWORDS

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** · 06-07-2020, 11:40 AM

Originally Posted by RSWORDS

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** · 06-07-2020, 02:22 PM

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** · 06-08-2020, 09:07 AM

Originally Posted by 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...

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** · 06-08-2020, 04:55 PM

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** · 06-09-2020, 07:04 AM

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** · 06-09-2020, 01:17 PM

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** · 06-09-2020, 03:01 PM

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

**LIGlastron** · 06-09-2020, 03:15 PM

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!