Absolutely frustrated with this Mercruiser engine

[Hoplite808]

Fuel pump, fuel, fuel lines, gas tank, etc.
you’ve ruled out engine and electrical. Only other thing is fuel (related).

The fuel pump is new, the vapor separator tank has been rebuilt and the fuel in the tank was siphoned out and replaced with fresh. Computer diagnostics could not find any electrical faults.

@370Dancer a spun bearing is unlikely in my circumstances. Oil pressure is good, no signs of metal in the oil or any other indicators of such a problem such as oil consumption.

 

[spikedaddy99]

Man I wish I had the ability to fix this. I'd be on a plane right now! I can't wait for you to be able to use this boat!

 

[Hoplite808]

OK got the injectors back from BAM Marine today. The testing results were as follows.

I'll let you all know if there is any improvement once I can get them reinstalled.

 

[Hoplite808]

Reinstalled the cleaned and tested injectors and absolutely no difference made. Sharing the data from the Fox Marine reader:

Engine running smoothly at idle:

First run at max speed attainable and holding at full throttle:

Second run again after maximum speed attained and holding at full throttle.

Not really sure what to do next now. Anyone see anything here that looks suspect?

 

[Hoplite808]

Additionally I revved the engine in neutral up to about 4000 RPMS. Engine sounded fine and without the load of the prop pushing the boat it revved up easily.

 

[Chris-380]

To me, (an uneducated boater) fuel flow is way low for 100% throttle but doesn’t seem crazy low for 2000 rpm (I think I am at 35 gph on plane at 25 mph which I think is about 3500rpm, complete guess from memory)….

I am sure it was spoke about, and I believe it was fine, but what was the fuel pressure (and was it pretty steady?) at the rail when running up the throttle like this

Reinstalled the cleaned and tested injectors and absolutely no difference made. Sharing the data from the Fox Marine reader:

Engine running smoothly at idle:
View attachment 144121
First run at max speed attainable and holding at full throttle:
View attachment 144122
Second run again after maximum speed attained and holding at full throttle.
View attachment 144123
Not really sure what to do next now. Anyone see anything here that looks suspect?

 

[Scott215]

Should the manifold pressure and the barometric pressure be the same it shouldn't be manifold pressure change when the throttle is open. It looks like the map sensor is given off almost the same reading as the actual barometric pressure reading

 

[Hoplite808]

To me, (an uneducated boater) fuel flow is way low for 100% throttle but doesn’t seem crazy low for 2000 rpm (I think I am at 35 gph on plane at 25 mph which I think is about 3500rpm, complete guess from memory)….

I am sure it was spoke about, and I believe it was fine, but what was the fuel pressure (and was it pretty steady?) at the rail when running up the throttle like this

Fuel pressure at the rail holds at 37 psi. This was tested with a mechanical gauge.

 

[PlayDate]

The idle data is really helpful and I compared the MEFI idle numbers to a couple of sources and they are approximately in range.

Specifically what I am looking at is the Injector On Time. At idle it is at 2.75ms. Under load it is 6.36ms and revving in neutral it is back to 2.70ms. The injectors are staying on longer but I believe the target needs to be 12.75ms (24lb injectors/454 ci/4000 rpm/350 hp) for 4000 rpm under load.

If we had a data sheet for another engine at 4000 rpm under load....I'm pretty sure we would see 12+ ms for the Injector On Time. As to why we aren't seeing 12+ms.....a data sheet for a working engine may highlight the sensor that the ECM is having issues with.

For example if we saw 12+ms Injector On Time and the engine did not go above 2000 rpm that would tell us that fuel pressure is the issue. You don't have that problem so it has to be a sensor hitting a limit and the ECM not increasing Injector On Time.

You are definitely closing in on the problem. I feel bad that you had to spend the money on the injectors.

 

[Chris-380]

Wow, great info. Thank you for sharing, I had no idea what a lot of info should be in my fox gateway, that def helps me with one of them.

The idle data is really helpful and I compared the MEFI idle numbers to a couple of sources and they are approximately in range.

Specifically what I am looking at is the Injector On Time. At idle it is at 2.75ms. Under load it is 6.36ms and revving in neutral it is back to 2.70ms. The injectors are staying on longer but I believe the target needs to be 12.75ms (24lb injectors/454 ci/4000 rpm/350 hp) for 4000 rpm under load.

If we had a data sheet for another engine at 4000 rpm under load....I'm pretty sure we would see 12+ ms for the Injector On Time. As to why we aren't seeing 12+ms.....a data sheet for a working engine may highlight the sensor that the ECM is having issues with.

For example if we saw 12+ms Injector On Time and the engine did not go above 2000 rpm that would tell us that fuel pressure is the issue. You don't have that problem so it has to be a sensor hitting a limit and the ECM not increasing Injector On Time.

 

[PlayDate]

Should the manifold pressure and the barometric pressure be the same it shouldn't be manifold pressure change when the throttle is open. It looks like the map sensor is given off almost the same reading as the actual barometric pressure reading

At wide open throttle......TPS and MAP are maxed....so manifold pressure and barometric pressure will be the same until the rpms increase. The crazy part .....spark advance and everything else looks good but the injector ON duration is where the problem is. For some reason the ECM is not telling the injectors to stay open longer.

It is almost like the ECM has gone into a Safe mode.......

 

[PlayDate]

To the last point (I believe the OP discovered this earlier):

RPM Reduction Mode The ECM recognizes a change of state in a discrete switch input that identifies an abnormal condition. During these abnormal conditions, RPM reduction mode allows normal fuel injection up to OEM specification (approximately 2000 RPM). Above the OEM specified RPM limit, fuel delivery is limited to half the fuel injectors until the engine drops below 1200 RPM. Then normal engine operation is restored until the RPM limit is exceeded again. This feature allows maneuverability of the boat while removing the possibility of high engine speed operation until the problem is corrected.

I'm trying to figure out how to turn this off.

 

[Ericinmich]

Should the manifold pressure and the barometric pressure be the same it shouldn't be manifold pressure change when the throttle is open. It looks like the map sensor is given off almost the same reading as the actual barometric pressure reading

At WOT the MAP and Baro should be about the same unless restristions in the intake somewhere (usually air cleaner).

I'll spend more time looking at the data...

 

[PlayDate]

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.

 

[Ericinmich]

Apologize for not reading all the posts, but any chance there is a restriction on the exhaust? I'm not sure if there is a port or easy way to read exhaust pressure. It sounds a bit like a car with plugges cat.

That said, if it's a hard 2000 RPM limit every time you go out, it's like the ECU pulling back fuel at that point. I use to have the SW listing for that ECU, not sure what the list of things that can put the engine into safe mode. It could be something as simple as thinking it's in neutral... or low outdrive oil or ??

 

[Hoplite808]

It's not in the "Safe Mode" though. If you look at the list the 23rd item down is Power Reduction. Its showing off in all of them. So it's not in "Safe Mode". Also the Fox Marine Unit requires a separate sensor to read oil pressure. I know for a fact that my gauge is accurate and its holding around 50-60 psi while running. There are not odd noises coming from the engine either and other than not exceeding 2000 RPM's under load it performs normally.

 

[Hoplite808]

Apologize for not reading all the posts, but any chance there is a restriction on the exhaust? I'm not sure if there is a port or easy way to read exhaust pressure. It sounds a bit like a car with plugges cat.

That said, if it's a hard 2000 RPM limit every time you go out, it's like the ECU pulling back fuel at that point. I use to have the SW listing for that ECU, not sure what the list of things that can put the engine into safe mode. It could be something as simple as thinking it's in neutral... or low outdrive oil or ??

The exhaust is not plugged. The entire leg was replaced less than a year ago. I changed both exhaust manifolds and while they were off I changed the flapper valves in the Y-Pipe and observed no indication of any obstructions.

 

[hughespat57]

One thing we need to understand when interpreting these numbers is which are truly measured and which are calculated.

Sensor voltages such as the TPS are referenced to 5v
TPS Voltage - 4.24 indicates the position of that sensor
Throttle % - 96.48 is calculated from the TPS value, because it is more easily understood than the voltage

Fuel Flow Rate is a calculated number, from the "Injector on time" 6.36 ms and RPM
There is no true flow meter. The ECM uses a table that is based on what the injectors should be flowing given the open time and RPM.

With the throttle at 96.48 % open, there should be almost no "Vacuum" air is free flowing. So the MAP sensor is at 4.92 volt which ECM calculates to 30.40 inHG. This matches ok.

From a flow chart at 2000 RPM a 7.4 should be flowing approx 7GPH so that is good.
At WOT under full load it should be at 25GPH +/-

The throttle IS wide open this engine should be running lean and detonating, but no Knock retard.
I'm with @Ericinmich, the engine is not breathing correctly.
Exhaust issue perhaps.
Or the camshaft timing is off.

@Hoplite808 When you did all that head work did you have the timing chain off at all?
If not I think you still have valve issues.
I know you did compression but good numbers for a 454 would be closer to 150.

 

[Hoplite808]

@hughespat57 I did not mess with the timing chain at all.

 

[PlayDate]

It's not in the "Safe Mode" though. If you look at the list the 23rd item down is Power Reduction. Its showing off in all of them. So it's not in "Safe Mode". Also the Fox Marine Unit requires a separate sensor to read oil pressure. I know for a fact that my gauge is accurate and its holding around 50-60 psi while running. There are not odd noises coming from the engine either and other than not exceeding 2000 RPM's under load it performs normally.

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.