Mercury 200 EFI, am I hitting a rev limiter?

[bbarthelt]

Hi all. Engine is a 1996 200hp EFI, serial number 0G361511.

Symptom: While accelerating and as speeds approach the upper 40s / 50s, the boat intermittently loses power for a split second and resumes. At first I thought it seemed to coincide with hitting bumps on the water. Now I think I might be wrong about that. It seems to happen only at higher speeds, and far more often/consistent if I trim up. Sometimes it does coincide with bumps, but other times not. The loss of power is a split second. It feels like i'm hitting a rev limiter OR as if a wire has a shaky/lose connection.

Relevant data
1. This engine was recently transferred from one boat (a 1996 Charger 295TF) to another (1993 Nitro 2000DC). The symptom was present on the charger and has continued on the Nitro.
2. The symptom is present with any prop I've tried: I have 23, 24,and 25 pitch Tempest Plus props. the issue is identical regardless. Hole shot is outstanding with all props.
3. The symptom is present with any amount of fuel in the tank.
4. I noticed voltage is under 12v when running (11-ish) and tach stopped working. Friend-of-friend boat mechanic said that's a sign of a bad voltage regulator so I have that ordered and will change it.
5. In an attempt to debug this (and get more performance) changed the ECU from stock to a Brucato and the symptom persisted. Now that I know my stock ECU was not the issue, I will sell it. But at least I know it's not the ECU.
6. When the motor was transferred to the other boat, compression was checked, injectors serviced, fuel pump and impeller replaced.

Questions
1. Could a failed voltage regulator create such a symptom?
2. I know there is a rev limiter in the ECU (brucato adjusted mine), but is there another form of rev limiting that I could be hitting? Could timing or setting on any of the various throttle/idle/etc. set screws affect this?


I will have an entire day on Friday to install the new voltage regulator and try other solutions.

Thanks in advance for any help.

[leonreno]

It would be hard to tell without knowing the rpms you’re at. Could be the low voltage causing the problem too. Fix the known problems and then retest. Could use a “Tiny Tach” to test rpms, it’s temporary tach you hook to spark wire to check rpms, usually accurate and fairly cheap. Also could be fuel starvation, read the FAQ about fuel problems and fuel lines.

[bbarthelt]

Thanks leonreno. That reminds me of another data point:

I had new fuel lines put in when the motor was swapped to the other boat. The fuel lines were ancient, and the kind that get eaten by ethanol. I'll definitely swap that voltage regulator, just hoping to get some "what to try next" ideas if that doesn't do the trick. Thanks again all.

[kls2020]

Low voltage could be a stator issue or a voltage regulator issue . A shorted diode in a voltage regulator will cause electrical noise in the battery voltage that can do weird stuff to electronic stuff . I also remember somebody discussing problems with an efi motor checking all kinds of components only to later find out it was a bad battery that was the problem . A faulty charging system will turn a good battery into a bad undercharged one though. Tach gets it's signals from the voltage regulator so that could be a clue .

[JOE54]

if voltage is not above 14 when running theres a problem

[SilverFox579]

if voltage is not above 14 when running theres a problem

[bbarthelt]

New voltage regulator arrives tomorrow, and I'm testing Friday. Thanks for the tip on the stator as another possible culprit.

I'm also suspicious that one or more of the timing/ICS/TPS/throttle set screws. I had an issue getting on plane after a power head 18 months ago that turned out to be the guy set the throttle limiter screw wrong. So I'm having a guy do the full timing setup as soon as he has a moment.

[bbarthelt]

New top voltage regulator installed (it has two). There were definitely some melted wires. I'm now getting 13/14 volts, and tach works again, but the problem persists. Convinced my timing is jacked and it thinks i'm hitting the rev limiter. Waiting on mechanic availability, but would love if any experts here feel that this theory holds water. Thx.

[leonreno]

I I’ll say the experts usually recommend replacing regulators in pairs because if one went bad the other might be damaged too. Have you checked the timing with a timing light. Highly recommend buying a Mercury service manual which will have all the troubleshooting techniques needed for this.

[JOE54]

how many rpm is it turning exactly

[SilverFox579]

I I’ll say the experts usually recommend replacing regulators in pairs because if one went bad the other might be damaged too. Have you checked the timing with a timing light. Highly recommend buying a Mercury service manual which will have all the troubleshooting techniques needed for this.

Excellent advice.

[bbarthelt]

Thanks guys. I did order the 2nd VR, will be here in a couple days. This happens right at 4000 RPMs. I made a video, link below. If I push the throttle past 4000, OR I trim up and RPMs rise to 4000, this kicks in. You can see the first occurrence at 39 seconds of the video in the link below, then it happens repeatedly:

https://drive.google.com/open?id=1z2...EEMi6AGif-NPeX

I've read the timing procedure online. At this point I have to be honest and say it's beyond my skill level. I've reached out to a mechanic to have him set timing, waiting on his availability.

[leonreno]

That’s beyond anything I know, but it’s definitely doing something. Could maybe be Throttle Position sensor, maybe.

[JOE54]

what does it do if no trim is used

[bbarthelt]

if I keep the throttle so that the RPMs stay below around 4000 and leave the trim down, it just cruises along at about 38mph. Trimming up seems to let the RPMs go up, and then it kicks in. This is why I'm thinking it's hitting the rev limiter. I'll look into the Throttle Position Sensor. Thanks again guys. Any other suggestions appreciated.

[123trentm]

High side of stator?

[JOE54]

remove advance module and idle stabilizer put stock ecu back on , clean cannon plug connections, check all grnds on mtr and batt also check fuse connection above solenoid

[kls2020]

You are getting lots of good suggestions of things to check so be systematic and check them off one at a time . After watching your video and noticing how rythmic the motor was in and out made me think of a fuel problem (momentarily running out of gas due to a restriction ) . Have you checked your fuel rail pressure yet to see if it is running steady at rated pressure or is pressure oscillating like your engine speed is at that RPM ? Did you change the spinoff fuel filter when you changed the engine hoses ? Ethanol melts the liner on the inside of the fuel lines and it can clog up any screens or filters .

[JOE54]

+1

[bbarthelt]

JOE54...are you suggesting removing the timing advance module & idle stabilizer permanently?