Absolutely frustrated with this Mercruiser engine

I saw that but I don't believe it. Literally the injectors are not being told to increase duration when every other sensor is telling the ECM to do that exact thing. Even if it was a timing chain issue or an exhaust issue.....the ECM would advance the injector duration. What other sane explanation is there? At almost exactly 2000 rpm the ECM stops the injectors from advancing which is why there is no rpm increase. Revving in neutral is not same thing since the injector ON duration never gets close to 6ms.

What I am suggesting is that with all the work you have done....one or more of the "discreet" sensors were disconnected. I don't doubt your oil pressure is fine.....but if there is a sensor that is disconnected nearby.....that would explain it.

As to why the Fox Marine unit would not pick it up that is more about how they would see it. The way most of these systems work is to convert voltages into measurements. The list of discreet sensors that they report on (two) do not include all the ones (six) on the list and the MEFI-1 is from 1996 which was 27 years ago. So I do question how they would know if a discreet sensor was unplugged when the manual calls for ohm testing every discreet sensor.

At some point....you have to look at the data ask yourself what scenarios actually fit the problem. To me....only the ECM controls the injectors and there is a direct correlation between Injector On duration and if the engine will spin up.

If you doubt it....find another engine that is working and hook your Fox Marine Unit up to it. What you will see is under load the injector On duration will increase smoothly up to 4000 rpm probably reaching 12-13ms of duration.

As to below 2000 rpm....the Safe mode was designed to operate completely normally below 2000 rpm which it appears to be doing perfectly.

Just my thoughts.


I'm with you on this. If it were mine, I would definitely go deep down this rabbit hole. I'm betting there is a rabbit at the bottom of this one.
 
Hoping to take my mefi3 out this weekend and look at these numbers. It isn’t the exact same, but should show what you are talking about, correct?

I saw that but I don't believe it. Literally the injectors are not being told to increase duration when every other sensor is telling the ECM to do that exact thing. Even if it was a timing chain issue or an exhaust issue.....the ECM would advance the injector duration. What other sane explanation is there? At almost exactly 2000 rpm the ECM stops the injectors from advancing which is why there is no rpm increase. Revving in neutral is not same thing since the injector ON duration never gets close to 6ms.

What I am suggesting is that with all the work you have done....one or more of the "discreet" sensors were disconnected. I don't doubt your oil pressure is fine.....but if there is a sensor that is disconnected nearby.....that would explain it.

As to why the Fox Marine unit would not pick it up that is more about how they would see it. The way most of these systems work is to convert voltages into measurements. The list of discreet sensors that they report on (two) do not include all the ones (six) on the list and the MEFI-1 is from 1996 which was 27 years ago. So I do question how they would know if a discreet sensor was unplugged when the manual calls for ohm testing every discreet sensor.

At some point....you have to look at the data ask yourself what scenarios actually fit the problem. To me....only the ECM controls the injectors and there is a direct correlation between Injector On duration and if the engine will spin up.

If you doubt it....find another engine that is working and hook your Fox Marine Unit up to it. What you will see is under load the injector On duration will increase smoothly up to 4000 rpm probably reaching 12-13ms of duration.

As to below 2000 rpm....the Safe mode was designed to operate completely normally below 2000 rpm which it appears to be doing perfectly.

Just my thoughts.
 
@PlayDate This is great info, thank you for sharing it.

After diving into this manual, I see why you turned to some jack.

I have no experience with this at all. So I am asking dumb questions. At the opposite end of the connector, are these optional wires just sealed off or is there a dip switch you must flip for the ecm to look for the sensor (0/1) open or closed?


Is this something the scan tool will show where the fault is?

IMG_7980.jpeg
IMG_7981.jpeg
IMG_7982.jpeg
IMG_7983.jpeg

So it is quicker for me to type in the MEFI-1 ECM inputs.

Battery 12v
Ignition 12v
TPS
MAP
Coolant
IAT
Knock

Diagnostic Enable
Water Flow (optional)
Trim position (optional)
Trans temp (optional)
Oil Level (optional)
Oil Pressure (optional)
Emergency stop (optional)
I/O fluid level (optional)
RPM


IF it is in Safe mode.....one of these sensors is the problem. If I had to guess....I would bet it is expecting to see one of the optional sensors. The ones in Bold show up working on the Fox gateway.

According to the MEFI-1 manual it shows all the "discreet" (optional) switches to be normally open in their normal state except for water flow which is normally closed.

Page 25 of this link same published year as his boat:

https://marinepowerusa.com/wp-conte...NJECTION-MEFI-1-2-5.7L-350CID-8.2L-502CID.pdf


I don't know if it is the original MEFI-1 or not. Assuming that it is means that the ECM is expecting to see one or more of the optional sensors. Specifically given the age.....oil pressure would be at the top of my list to check. Keep in mind that the normal state is with the engine running. If a sensor is disconnected when the engine is started it will stay in a Safe state.

I'm going to find my bottle of Jack Daniels and have a drink.
 
I know this is petty, but with out an actual scan tool, could there be a possibility of "diagnostic blindness"? This is when a single technician is stumped on a problem, he / she becomes blind to the obvious. The tech is "sure" something was checked at the beginning and out of frustration keeps overlooking an obvious problem. That is when a 2nd tech steps in and rechecks everything and quite often finds an obvious problem.

Since it was stated that there are no Mercruiser Techs available in HI, The scan tool can be considered the 2nd tech in this sort of situation. I know that the OP is using the systems data point, but that is not near as inclusive as the Rinda diagnostic software. The Rinda software was suggested early on and it was stated it was a cost prohibitive option. That threshold has probably been breached at this point and the situation still has not improved.

Suggest getting another set of eyes or proper diagnostic software.
 
Probably not this simple, although I will chime in. Took our 340 to our regular mechanic 2 weeks ago to have drives serviced. Had plugs and wires changed on port motor, did stbd last year, and when they put it back in water and we went for test run that motor, port, would not get over 2800 rpms. Took it back to the marina and it turned out to be a bad set of NEW plug wires. Not sure how they tested them. There were no errors codes, alarms, nothing from the Vessel View. It just said "System ok".
So I asked what they did to figure it out. They switched plug wires with the other motor and the problem followed. Changed the wires and all good. Guess question would be are you absolutely positive you are firing on all cylinders? With no codes, it has to be something fuel or firing related.
 
Hoping to take my mefi3 out this weekend and look at these numbers. It isn’t the exact same, but should show what you are talking about, correct?


Yes. You will see the same relationships and even more information. Specifically, 3500-4000 rpm would be really helpful.
 
@PlayDate This is great info, thank you for sharing it.

After diving into this manual, I see why you turned to some jack.

I have no experience with this at all. So I am asking dumb questions. At the opposite end of the connector, are these optional wires just sealed off or is there a dip switch you must flip for the ecm to look for the sensor (0/1) open or closed?


Is this something the scan tool will show where the fault is?

View attachment 144162 View attachment 144161 View attachment 144160 View attachment 144159

Chris,

To answer your other question on dip switches......each ECM is tuned for the marine application. So there are no dip switches since the software is loaded for the engine and boat that it is in. That's why you can't pull an ECM out of one boat and put it into another and expect it to work unless they are identical boats ......same goes with cars from the same manufacturer.

That's why I was wondering whether or not the ECM was original or not.
 
This photo from Post #81 is what is troubling me about the engine wiring. I can't tell what sensors these wires go to but in retrospect.....if one of these connections goes to a discreet sensor.......you will have a problem.

index.php
 
That's why I was wondering whether or not the ECM was original or not.

That's exactly where my logic went.

The only other thing that's throwing me for a loop is that engine vacuum is reading high at 2000 rpm. The boat shouldn't be on plane at 2000 rpm, which means that engine load should be high at 2000 rpm and vacuum should be low.
 
This photo from Post #81 is what is troubling me about the engine wiring. I can't tell what sensors these wires go to but in retrospect.....if one of these connections goes to a discreet sensor.......you will have a problem.

index.php

Those wiring pigtails usually go to analog sensors ie water temp or oil pressure.
 
That's exactly where my logic went.

The only other thing that's throwing me for a loop is that engine vacuum is reading high at 2000 rpm. The boat shouldn't be on plane at 2000 rpm, which means that engine load should be high at 2000 rpm and vacuum should be low.
That value is manifold Absolute pressure, meaning it's based on true zero, not atmospheric. I know it's a bit hard to wrap your head around after thinking of manifold vacuum sucking the gauge down to a higher number, like we're used to seeing on most hand-held and car vacuum gauges. If you'll look back at the idle numbers, the MAP is showing around 17", whereas atmospheric is around 30". That shows that the engine is pulling the manifold down closer to a full vacuum (0 inches). The closer those two numbers (manifold vs. atmosphere) are to each other, the heavier the load seen on the engine. Assuming everything's calibrated perfectly, the two would be identical with the engine not running.
 
That value is manifold Absolute pressure, meaning it's based on true zero, not atmospheric. I know it's a bit hard to wrap your head around after thinking of manifold vacuum sucking the gauge down to a higher number, like we're used to seeing on most hand-held and car vacuum gauges. If you'll look back at the idle numbers, the MAP is showing around 17", whereas atmospheric is around 30". That shows that the engine is pulling the manifold down closer to a full vacuum (0 inches). The closer those two numbers (manifold vs. atmosphere) are to each other, the heavier the load seen on the engine. Assuming everything's calibrated perfectly, the two would be identical with the engine not running.

I missed that it was MAP. MAP is referenced to barometric pressure. Duh... silly rabbit.
 
Thank you John, learning a lot in this thread. So if I wanted to add a couple sensors like water flow or transmission temp, I would need to get it reprogrammed, correct?

Chris,

To answer your other question on dip switches......each ECM is tuned for the marine application. So there are no dip switches since the software is loaded for the engine and boat that it is in. That's why you can't pull an ECM out of one boat and put it into another and expect it to work unless they are identical boats ......same goes with cars from the same manufacturer.

That's why I was wondering whether or not the ECM was original or not.
 
Thank you John, learning a lot in this thread. So if I wanted to add a couple sensors like water flow or transmission temp, I would need to get it reprogrammed, correct?

Yes. And frankly I am sure there is someone out there who does it. That said....I would probably find another way to display water flow. Too many threads on CSR are based upon the water flow sensor going bad and throwing the ECM into Safe mode miles from home.
 
Thank you John, learning a lot in this thread. So if I wanted to add a couple sensors like water flow or transmission temp, I would need to get it reprogrammed, correct?

You could always add N2K sensors (or analog to N2K) and tie the data into you MFDs that way.

-Kevin
 
Are you able to get a graph of the data from idle to the 2000 RPM point? I'd be curious if you hammer it down does it go slightly higher then down to 2k as if the system is controlling to that point. If so, it really has to be a safe mode. It's not likely a fuel flow or air flow issue would go to exacly 2000 rpm. I'm with outhers, just because the scan tool shows no safe modes (or faults), it may not be decoding the bits/bytes for those fields.
 
Are you able to get a graph of the data from idle to the 2000 RPM point? I'd be curious if you hammer it down does it go slightly higher then down to 2k as if the system is controlling to that point. If so, it really has to be a safe mode. It's not likely a fuel flow or air flow issue would go to exacly 2000 rpm. I'm with outhers, just because the scan tool shows no safe modes (or faults), it may not be decoding the bits/bytes for those fields.


Check this out....page 126 of MEF1-1 manual.

Notice: The sensors that trigger Safe mode do not throw DTCs (It was 1996). You would need a tester (which there is a very direct note about at the top of the first page) that could see the voltages on those pins (J1-19, J1-20, J-21, J-22, J1-4 and J1-6). Even then, you would still need to know which sensors the ECM was expecting to see.

About the only way to solve it is go to each location where a sensor is supposed to be and locate it/check the wiring for continuity back to the ECM. Fortunately there are only six of them and three should be on the engine and two should be on or near the drive. The last one is on the helm if it is installed.
 

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