91 merc 175 xri efi seems to hit rev limiter above 4000rpms

[davec99]

the motor runs great, if i keep the rpms under 4000. as soon as they go over 4k, it seems ti hit a rev limiter or kill switch. when it starts to cut off, if i let back a little, so its below 4k, it runs great and can pull 2 people on a tube. if i keep it trimmed down and accelerate while holding the trim button down, i can get a few hundred rpms for a short time, then it starts to act up again above 4k.
the wierd thing is, at one point, i was able to actually get the motor to 5000 rpms and almost 60mph. i had about 1/4 tank of gas and stayed steady at 3000 rpms for a few minutes, then quicky to wot.
i have done most clymer tests on the fuel and electrical. at this point i am thinking its the advance control module. i read something about a service bulletin being issued on this, and the module can be removed and advance timing to 23-25.
my other guess would be the trigger.
i am not comfortable enough to do the test at wot, so its been to 2 mechanics (or guys that have tools). the 1st did no water test, the 2nd tested it in the water, but on the trailer. on the trailer, i can go wot and get to about 4000rpms and it does not die or cut out.
any advice would be greatly appreciated.
some of what i have done
-rebuilt manual fuel pump
-replaced pickup tube
-replaced all fuel lines and bulb with blue hose
-had injectors cleaned and tested
-replaced stator, regulator, switch boxes
-cleaned vst filter (very clogged), changed all other fuel filters, flushed fuel system
-drained tank, cleaned, added fuel additives and 50:1 mercury premium plus
-pulled apart every electric connector, wire brushed male end, closed female a little, used grease when reinstalling. separated male pins also and used grease
- tested fuel pumps, regulator, tps, air sensor (by injectors), engine temp sensor (on head)
-replaced vst gaskets
-removed fuel quick connect and ran line from tank to mach pump
i am sure there are things im forgetting
Please HELP!!

 

[davec99]

Re: 91 merc 175 xri efi seems to hit rev limiter above 4000rpms

serial # is OD068605

 

[davec99]

Re: 91 merc 175 xri efi seems to hit rev limiter above 4000rpms

i just tested the pressure from the elecric fuel pump and to the pressure regulator. i used a closed end, no t, on a 100psi guage. the pump surges to max (over 100psi), then drops to about 70psi, then maxes and repeats for the cycle. i have looked but cannot find out what would cause my electric fuel pump to surge like this. the surging is exactly like the surging i feel at wot.

 

[davec99]

Re: 91 merc 175 xri efi seems to hit rev limiter above 4000rpms

i just spoke to a guy that rebuilds ecus. he said it could be the ecu sending a bad signal. $500 repair, any suggestions befor i send this out?

 

[davec99]

Re: 91 merc 175 xri efi seems to hit rev limiter above 4000rpms

good news is i found the problem, the high speed timing advance module is bad. the bad news is p/n 93772A3 is no longer available. anybody know where i can get a module? either aftermarket or new is ok

 

[davec99]

Re: 91 merc 175 xri efi seems to hit rev limiter above 4000rpms

Ok, its not the advance module.
It was working intermittently, both on low and high rpms. I removed it and re-set timing. It runs great in my driveway. with a full tank and 3 others, i get it to the lake and now i cannot smoothly get more than about 3000 rpm. It is still acting like there is a rev limiter, but hitting it faster. At WOT, the rpms will rev to about 3500, then drops to about 3000. Before i removed it, i was getting an extra 1000 rpms. I am at a loss and im tired of mechanics replacing parts at my expense. Any ideas would be greatly appreciated.

 

[Faztbullet]

Re: 91 merc 175 xri efi seems to hit rev limiter above 4000rpms

If that reading is correct on fuel pressure it way to high and that would be a regulator problem. Throw away the clymer manual and order a FACTORY one...

 

[davec99]

Re: 91 merc 175 xri efi seems to hit rev limiter above 4000rpms

I think one of my posts didnt post. The pressure was tested at the output of the pump. I put a different pump on and it held about 90psi. If i test the pressure when the engine is running, i get a steady 35-40 psi. Even as the motor cuts out, the pressure stays consistent. Im positive it is not a fuel issue.
Today, Im taking it to a shop that has a dyno. At this point, i think the guy i bought it from fried the stator by running with a bad voltage regulator. Im thinking the stator's low side loads up, but the high side is dead, making it act like a rev limiter. As i do research, i find these stators fail frequently due to the heat, as it is located at the top of the engine. I have a really good digital meter, but not the high voltage one to properly test the stator and switch boxes. To make sure its not a switchbox, i was going to take them off and reinstall them opposite the way they are. I dont know if thats a good idea or not.
Any input is greatly appreciated, thanks.

 

[davec99]

Re: 91 merc 175 xri efi seems to hit rev limiter above 4000rpms

The dealer called me today to tell me my ecu is bad. does anyone know if its better to buy a used ecu or get it re-built. if anyone has an ecu for a mercury 175xri efi, please let me know.

 

[Mercury1010]

I have a 96 200 that's doing the same thing . Did new ecu fix it?