Odd TPS Error Behavior Montauk 150

[dbtfree15]

I have a 2006 Montauk 150, powered by Mercury 60-HP Bigfoot, serial 1B004506.

I had some electrical problems that were caused by the engine charging system. I had to replace the regulator, stator and the starter solenoid, and the intake manifold air temp sensor.

Engine runs fine on muffs or in neutral in the water. The following behavior only happens under way after I get up on plane:

After I had all of this done the engine started working better than it ever did, in terms of coming up on plane and running between 3000 to 4000-RPM, between 18 and 21-MPH. Any time the engine speed exceeds about 3900-RPM, the engine has an intermittent behavior where the engine cuts out for a second, a single BEEP Iis heard, and then the engine comes right back. It is almost like the key was turned to OFF and then back to ON.

On the engine tachometer gauge and on the VESSELVIEW display, after the engine cuts out, the engine speed drops to 0-RPM, then goes immediately back up [to a reading of normal RPM such as 4,000-RPM]. This seems entirely unlikely, since there is no way the actual engine rotation speed goes from 4000-RPM to 0-RPM and back [to 4,000-RPM] that quickly.

If I keep it around 3900 or 4000, it will cut out and beep randomly and then come back, and maybe run normally for another ten minutes before it will do it again, randomly.

If I go over 4000, to say 4300, the engine will start [cutting out] more frequently, and if I go WOT, it will do it repeatedly every three seconds. The engine display then indicates code 341-6, throttle position sensor error code.

I have already replaced the throttle position sensor (TPS), and that did not change the behavior at all.

The only other change I have made, since it was running fine before electrical problems occurred, was I added a trolling plate that also has stabilizer fins.

See https://a.co/d/fQbfWUx.

I had wondered if the trolling was causing problems with water uptake, but that isn’t the errors I am getting and I have.


Give me suggestions [for how to remedy the problem of the engining intermittently utting out.

Note that providing gasoline from a new tank and fuel line didn’t seem to change behavior.

I am kind of at a loss..

I have replaced the TPS, the intake air temp sensor, the manifold air pressure sensor.

I have purchased a used ECM to see if it could be that—it’s in the mail—but seems unlikely.

If I am ok going 18-MPH boat speed and no more than about 3800-RPM engine speed, this 21-year-old 2006 Mercury 60-HP BIGFOOT engine works great—but I’d really like to sort this out.

[Phil T]

Note, be methodical. Start at the beginning and work forward. Throwing parts at the symptom is expensive and not always faster.

I would "google" the cr@p out of it on all the forums before buying another part.

The symptoms read as electrical but could be fuel related.

I would investigate the ignition circuit including the key switch and the kill switch.

[dbtfree15]

Thanks, that's definitely true. The stator, regulator, solenoid were all validated with readings, etc. The other three parts I changed cause I was right there when changing the TPS. I didn't test it, I did just replace based on the code, you're right.

I have been testing, including the ignition circuit for about a year now and can't find anything odd. The oddest thing is just that it only does once you're up on plane, under load. Should mention I cleaned the vapor separotor. I haven't rebuilt it (didn't replace the pump, just the filter in the foot and the one in the top of the VST) and replaced all of the fuel filters as part of regular maintenance. Did not see much crap in the filters, there was some black flecks/build up in the VST. But same behavior after, and running on small tank with new fuel line.

[GoldenDaze]

I just went through something similar, though I haven't taken the time to write up a report here yet. My 2003 Mercury 115 4-stroke would occasionally "stumble" briefly at cruise; as you said it was like turning the key off and then right back on very quickly. This progressed to where it wouldn't run above idle, and then finally to where it would only idle for 10-20 seconds. I spent the entire fall trouble-shooting this, including replacing the TPS sensor and the MAP sensor as well as the voltage regulator.

The problem turned out to be a slightly (and pretty much invisibly) corroded ground connector for the voltage regulator. This allowed the voltage to increase higher than normal once the engine was running, and when it reached approximately 15 volts the ECM would shut down (presumably due to over-voltage protection). Five minutes with a piece of 300-grit sandpaper fixed the whole thing.

This whole experience was like that old joke where a guy takes his car to the mechanic, the mechanic taps something with a hammer, then charges the guy $500. "$500 to hit it with a hammer? That's ridiculous!" "Nah, hitting it with the hammer was only $1. Knowing where to hit it was $499."

-Bob

[dbtfree15]

Bob, thanks, this is helpful. Guess I will try that next. :D How did you determine this? Have voltmeter on it while running and watch the volts hit 15v? Did you have the TPS error etc? Any beeps when it cut out?

[GoldenDaze]

It's a long story that I'll tell in detail in another post. But what finally got me on the right track was when I got the diagnostic connector and software, and saw that the ECM was shutting down, and then immediately boot up again. This might be what your beep is telling you. A few fortuitous tests, like disconnecting the voltage regulator (and then the engine ran fine!) led me to monitor the voltage more closely. Since both the old and new voltage regulator behaved the same, and the tests on the stator coils met spec, I double-checked the ground... and voila!

[dbtfree15]

Interesting, super helpful. I think might try the same thing there. Looking forward to your novella!

[jimh]

Based on your narrative describing the problem, my inference is the cause of this odd engine cutting out behavior is electrical in nature. Generally if an engine that is running normally instantaneously stops running--loses combustion--then immediately cures itself and resumes normal operation, the cause of the problem is likely to be electrical in nature. An immediate loss of spark in all cylinders is the only method that all cylinders in an engine stop firing immediately. A fuel restriction problem would be likely to begin to affect only one cylinder, then gradually affect other cylinders, resulting in a gradual decrease in power output by the engine, not an immediate and sharply defined cut off.

Electric circuits are often affected by temperature, and as the temperature increases, a problem can occur. However, the problem will not tend to disappear instantaneously shortly after onset, as there is unlikely to be any change in temperature--a cooling down of the electrical components--that can occur in a very short period of time.

Also, the apparently continued operation of electrical gauges showing engine speed while the engine has cut out tend to indicate that the electrical problem is confined to the engine's electrical circuitry.

All of these assessments tend to point to a mechanical problem being the cause of the electrical discontinuity in the engine circuits. The correlation with engine rotation speed is also significant, as generally higher engine speeds may result in increased vibration of the engine or at least a change in the frequency of vibration.

For those reasons I suspect there is a loose connection somewhere in the engine wiring. The suggestion that the loose connection could be in the negative or ground circuit is also good advice.

For ideas for remedies to this problem, I suggest you read my article about possible faults in the electrical circuits related to engine starting and running as described in detail in my article in REFERENCE at

Engine Starting Circuits
https://continuouswave.com/whaler/refer ... Start.html

Follow all the circuit paths mentioned in the low-current circuit. Any interruption in the ignition key switch circuit would have the same effect as turning the switch to OFF from RUN.

You have not given any information about the engine other than its brand and horsepower. There are two basic types of outboard engines: four-stroke-power-cycle and two-stroke-power cycle.

If the engine is a four-stroke-power-cycle engine the generation of spark ignition pulses is typically controlled by a crankshaft position sensor (CPS). Any loss of signal from the CPS will suppress generation. An intermittent CPS could be causing this problem.

If the engine is a two-stroke-power-cycle engine the generation of spark ignition pulses is typically controlled by a dedicate coil assembly in the engine alternator stator windings. The signal from the dedicated coil winding is applied to additional electrical circuitry, which I believe in the Mercury realm is called a switch box. A fault in the switch box could cause interruption of spark generation.

Also, typically an outboard engine will have a engine-shut-off safety switch. These switches tend to rely on a mechanical method of retaining a lanyard in the RUN position. Check carefully that the engine shut-off safety switch lanyard is properly and completely seated in position.

ASIDE: my wife's car had what turned out to be an intermittent CPS. But its failure was heat related. The car would be driven on several short errands, then left to heat soak for a while. Then it would not restart. I would get a call, and come to the car to diagnose the problem. By then the engine had cooled down, and the car would start and run normally. This went on until my wife insisted we switch cars. The problem finally occurred while I was using the car. After some rudimentary checks--including discovery that the V6 engine was running on only five cylinders due to a bad connection at a spark coil--I could not find the cause of the problem. I then speculated the cause might be the crankshaft position sensor. Getting to the CPS was a bit of a chore, so I asked my local garage to please just replace the CPS, do not do any diagnostic time. For a rather modest labor and parts charge, they replaced the original CPS. The engine ran perfectly after that repair for many years, until we finally sold it. I mention this because loss of the CPS signal immediately stopped that engine from having any spark generation.

Also, when chasing the cause of problem and not having a certainty of which part is causing the failure, my general rule is to replace parts in reverse order of their cost, that is, replace the cheapest part first, the next cheapest is that does not work, and proceed in that order until you conclude with the most expensive part. As parts go, a CPS is not going to be very expensive.

[dbtfree15]

Thanks jimh, that article is helpful, will use in my investigation.

This is a 60hp EFI 4-stroke. I have not changed the CPS yet, will add to my list to test. I had similar experience with a Hyundai V6 where a failing catalytic converter, which results in higher heat in the cat which sits right over the CPS on that engine, cooked the CPS. Cats were more expensive than the car, so I moved on. :D

Did check the lanyard thing, seemed mechanically sound (not saying it couldn't be a connection). I also tried flipping it on and off real fast, and wasn't quite the same behavior (no beep). The behavior really feels like the the key gets turned on and off real fast. So this ground/connection this starting to make me think it is a possibility. Going through grounds is pretty straightforward, looks like I might be in for some work if I need to go through every other connection.

Thanks!