Mercury 175 XRi ECU on 200 EFI

Hi Guys,

Ive been encountering issues with my 200 efi lasts weeks. It suddenly started to idle rough and i lost a small amount of top speed (about 2 mph). Furthermore the engine has lots of power and feels strong.

Replaced/rebuild: Pulse fuel pump, VST, reeds (boyensen), checked spark on plugs.

Today i swapped the 200 ECU with a 175 XRi ECU. I did test in on the hose and it appears to idle fine suddenly. Again, this was on the hose and not in the water.

My question: would a faulty ECU be able to create such a situation where it idles like Sh*t, but still works great on other RPM's?

Also: Whould it be okay to go for a test run with a 175XRi ECU on the 200 Block? Would it be lean? Or would it be okay in practice?

Thanks!

have you checked the tps and done a link n sync?

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Originally Posted by killerpirate

Hi Guys,

My question: would a faulty ECU be able to create such a situation where it idles like Sh*t, but still works great on other RPM's?

Also: Whould it be okay to go for a test run with a 175XRi ECU on the 200 Block? Would it be lean? Or would it be okay in practice?

Thanks!

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yes, it could..........

run it like ya stole it...... you'll never know till ya try it... merc was not to "hands on" with they're quality control with tha ecu's, soooooooooo......................

don't think they understood tha word "lean" with anything they (production) built except some ecu's that had a lean spot at certain rpms.. again tha QC process!

So it would be fine to taken it for a testrun?

Did not test the tps, cause i dont have the test harnass. Been thinking about doing it eithout the harnass, but i cant think of any way to reach the terminals :)

Sync & Link, that is the sequence where you set all the timing and throttle valves to spec, correct? Section 2c-10 to 2C-18 of the service manual?

I have this manual: https://www.google.com/url?sa=t&sour...-5yhx4Y5LSRv_u

that one is for tha 2000 ('lectronic motors) and up.. what year is yours?

Quote:

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Originally Posted by killerpirate

So it would be fine to taken it for a testrun?

Did not test the tps, cause i dont have the test harnass. Been thinking about doing it eithout the harnass, but i cant think of any way to reach the terminals :)

Sync & Link, that is the sequence where you set all the timing and throttle valves to spec, correct? Section 2c-10 to 2C-18 of the service manual?

I have this manual: https://www.google.com/url?sa=t&sour...-5yhx4Y5LSRv_u

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To test idle yes, full throttle no
unless You add an adjustable pressure regulator to pump up the pressure
And having an egt gauge with alarm is really great
https://youtu.be/_s_7rLZsgdw?si=sbAw0QyY3rzCwsvz

all that fancy 'lectronic stuff wasn't even on tha drawin' board when we used "real world" testin''... jus sayin'.................

ecu doesn't have anything ta do with fuel pressure anyway.......... thats all on tha pump and regulator..... it jus tells tha pump when ta run.

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Originally Posted by tlwjkw

all that fancy 'lectronic stuff wasn't even on tha drawin' board when we used "real world" testin''... jus sayin'.................

ecu doesn't have anything ta do with fuel pressure anyway.......... thats all on tha pump and regulator..... it jus tells tha pump when ta run.

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It has when you use a 175 ecu on a 200

we will have ta disagree on that.. any ecu 150/175/200/promax, all have tha same pump circuit... it turns 'em on or turns 'em off..... tha 175 is not special..........

bobby v. has ran every combination possible with horse powers and ecu combinations.. they usually ran tha same no mater what was on what... if it was bad on one it would be bad on tha other and vice versa.... there was never a lean or fat change at all.

jus remembered one thing though.. some would show a slight change in max rpm... but not enough ta mater much for a production motor.......

I don't mean the pump running circuit, i mean the fuel curve inside the ecu for the designated horsepower
You might get away with the 25hp difference but it could also mean a melted piston
https://youtu.be/7XTil1msFIc?si=gfPnE35hEJ7r8GwE

This is how that looks, really ruines your day
In this case it was aftermarket injectors deviating to much but the idea is still the same
Having a horn scream at you when your egt's are to high is ver good to have

I have an xr6 150 I bought from a bass boat guy who ran a 200ecu on for years no issues. He didn’t even know it wasn’t the right one for his motor he didn’t service it himself this was installed during maintenance when what sounds like a driver issuer on his factory ecu failed. Said it ran the same.

I’m about to try a 225 ecu on a 200 and see how that goes

That would be putting a richer ecu ( more horsepower more fuel ) on a lower horsepower engine needing less fuel
You might loose some horsepower from the richer curve but it is not going to brake it

after years and years and years of runnin' justa 'bout anything on anything between myself and bobby neither of us have ever "melted" a motor down because of a lean condition.......... jmo.

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Originally Posted by PanRonnie

That would be putting a richer ecu ( more horsepower more fuel ) on a lower horsepower engine needing less fuel
You might loose some horsepower from the richer curve but it is not going to brake it

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has nothing ta do with pressure which i thought you were sayin' tha ecu could regulate....

Very true. Using a bit more fuel would probably not even register. I am blown away how much fuel my 200 uses at 3/4 throttle, vs full throttle. It’s not a little more it’s probably five times more fuel at full throttle. I guess that’s how it goes when using enrichment as the rpm limiter. Crazy

I also feel the differences between the 2.5 fishing motors be it 150/175/200 are more about stickers than actual differences in the motors themselves. Think about it. All the fishing motors except for the F have four or five petal front half’s which are the same size intake openings. The biggest differences I can see is in the block castings are between the small and big chests. EE is a small chest yet runs a 200 ecu. CC looks to be the same block with reliefs in the sleeves. FF is different sleeves and bigger chest yet runs great on the same 200ecu lol. Promax 225 is a seven petal though so my thinking is it is calibrated richer. Among the four and five petal motors they are so very similar I can see how any ecu would probably run fine on any 2.5
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