Mercruiser 4.5l low vacuum, WOT 4350 and higher fuel consumption

[damo79]

The range for WOT RPM is 4800-5200, so 5,000 is a good target.

Are we at altitude? MIL sitting in the back?

No MIL. I weighted the boat with trailer to see if there is extra weight like foam soak with water.
BTW fuel consumption at 3000rpm doesn't change much if I run it alone or with 5-6pax maybe by 10%. Same with max speed
Its at sea level

 

[muc]

A few things I should point out for future reference.
@damo79 has a DTM engine not the DTS engines that @tpenfield has.
A DTM engine has a mechanical throttle control at the helm and a mechanical throttle and shift cables going back to the shift plate on the engine. Also this is a non cat engine.
This changes more then a few things on how we troubleshoot and importantly how we read Diacom files.

But looking at the REC files we have at this point might be a waste of time -- they might be corrupted.

It is to be expected that the PCM won't open the throttle plate 100% when RPMs won't get above 4500 with a full load. The PCM won't feed more air then the engine can use. Most everything on this engine, spark, amount of air supplied to engine and amount of fuel supplied to engine are controlled by the PCM. And the PCM is using many things to make decisions.

What we are looking for, is basically why this engine won't reach WOT.
Let's assume this boat should reach 5200 RPMs @ WOT (or close) like the test boat did with a 19p aluminum.
5200-4300=900 RPMs
1/6ᵗʰ of 5200 is 867 RPMs
Maybe we have a cylinder not doing anything?

 

[damo79]

A few things I should point out for future reference.
@damo79 has a DTM engine not the DTS engines that @tpenfield has.
A DTM engine has a mechanical throttle control at the helm and a mechanical throttle and shift cables going back to the shift plate on the engine. Also this is a non cat engine.
This changes more then a few things on how we troubleshoot and importantly how we read Diacom files.

But looking at the REC files we have at this point might be a waste of time -- they might be corrupted.

It is to be expected that the PCM won't open the throttle plate 100% when RPMs won't get above 4500 with a full load. The PCM won't feed more air then the engine can use. Most everything on this engine, spark, amount of air supplied to engine and amount of fuel supplied to engine are controlled by the PCM. And the PCM is using many things to make decisions.

What we are looking for, is basically why this engine won't reach WOT.
Let's assume this boat should reach 5200 RPMs @ WOT (or close) like the test boat did with a 19p aluminum.
5200-4300=900 RPMs
1/6ᵗʰ of 5200 is 867 RPMs
Maybe we have a cylinder not doing anything?

Well explained with the throttle opening at WOT and it makes sense.

One cylinder doing nothing crossed my mind before. What I checked before I purchased Diacom was disconnecting cables to spark plugs one by one. Engine was running rough noticed higher fuel consumption at idle in Vessel View and after a while it triggered misfire alarm. If one cylinder wasn't working o2 sensor on that side sensor will probably see more oxygen and adjust fuel trims. Right?
Its got to be something common if o2 and fuel trims, injector pulses are the same for both sides of the engine. Thought about ignition coils (common for 2 sides) but if one was bad misfire alarm should come off?

Attached are options I can see in Diacom for engine tests when ignition is on. Maybe there's a way to activate them, not sure. I believe that cylinder drop test is very handy

 

[nola mike]

A few things I should point out for future reference.
@damo79 has a DTM engine not the DTS engines that @tpenfield has.
A DTM engine has a mechanical throttle control at the helm and a mechanical throttle and shift cables going back to the shift plate on the engine. Also this is a non cat engine.
This changes more then a few things on how we troubleshoot and importantly how we read Diacom files.

But looking at the REC files we have at this point might be a waste of time -- they might be corrupted.

It is to be expected that the PCM won't open the throttle plate 100% when RPMs won't get above 4500 with a full load. The PCM won't feed more air then the engine can use. Most everything on this engine, spark, amount of air supplied to engine and amount of fuel supplied to engine are controlled by the PCM. And the PCM is using many things to make decisions.

What we are looking for, is basically why this engine won't reach WOT.
Let's assume this boat should reach 5200 RPMs @ WOT (or close) like the test boat did with a 19p aluminum.
5200-4300=900 RPMs
1/6ᵗʰ of 5200 is 867 RPMs
Maybe we have a cylinder not doing anything?

Shouldn't the PCM be able to detect this? It has misfire counts on there and a CPS.

If one cylinder wasn't working o2 sensor on that side sensor will probably see more oxygen and adjust fuel trims. Right?

I'd think so, and don't know if/when mercruiser uses crankshaft acceleration numbers to determine if there's a problem with a cylinder.

 

[damo79]

@muc I compared few things in Diacom with 6.2l V8 bigger brother same contruction. I know different boat, different drive, props etc. But just looking at idle vacuum is the same. You were probably right not every engine is the same and not everything what mercruiser prints in service manual is applicable (that's not good BTW). I can only see that my engine runs reacher from 3000rpm (o2 target) and runs out of breath sooner at 4400 MAP = BARO, and PCM retards spark advance sooner. More fuel consumption probably dictated by vacuum dropping down sooner than it should in healthy engine. Seems that im back to square one. Overloaded or worn out engine? Strange with good compression. I will check the drive at some point.
I will also install new battery this week and run Diacom logs again.

 

[muc]

Well explained with the throttle opening at WOT and it makes sense.

One cylinder doing nothing crossed my mind before. What I checked before I purchased Diacom was disconnecting cables to spark plugs one by one. Engine was running rough noticed higher fuel consumption at idle in Vessel View and after a while it triggered misfire alarm. If one cylinder wasn't working o2 sensor on that side sensor will probably see more oxygen and adjust fuel trims. Right?
Its got to be something common if o2 and fuel trims, injector pulses are the same for both sides of the engine. Thought about ignition coils (common for 2 sides) but if one was bad misfire alarm should come off?

Attached are options I can see in Diacom for engine tests when ignition is on. Maybe there's a way to activate them, not sure. I believe that cylinder drop test is very handy

For people following along, I would never advise a cylinder drop test be done by pulling spark plug cables on a EFI engine. Unless you have a waste spark, non cat engine like @damo79 has.
When doing this test, it will work best around 1500 RPM under load. Don't bother looking at fuel burn -- the PCM will be compensating for the loss of a cylinder. Look instead at RPM, you are looking for about the same RPM drop on each cylinder.

It's good to know that misfire faults can set. This being a non cat engine the misfire monitor won't run in the background like a cat engine would. So any data in the misfire counters in Diacom isn't trustworthy.
Also the misfire fault is a 2 trip fault, this means the PCM will need to so excessive misfires during 2 run cycles. Note that to start a new run cycle on this engine -- key off for 15-20 minutes or key off and shift to full throttle reverse.

Yes I agree that a missing cylinder would cause fuel trim to be adjusted.
But remember the fuel monitor only runs during closed loop, so can only adjust fuel while in closed loop. Also note that Diacom can display closed loop and the engine really isn't in closed loop, both O2 sensors need to be in adapted mode and neither can have a phi of 0.98.

If one coil was bad and you lost 2 cylinders --- wouldn't get to 4400 RPM under load.

If it's "grayed" out like that, it's just not available on Diacom. It is available in G3. Just one of the many differences.

 

[muc]

Shouldn't the PCM be able to detect this? It has misfire counts on there and a CPS.


I'd think so, and don't know if/when mercruiser uses crankshaft acceleration numbers to determine if there's a problem with a cylinder.

Misfire counters show up in Diacom, but because this engine doesn't have a cam sensor and cats --- any info you see will be bogus.

This engine has a 56x reluctor wheel. So when the proper conditions are met it will adjust fuel and timing to each cylinder separately. It will try to keep each cylinder at the same power output.

 

[muc]

@muc I compared few things in Diacom with 6.2l V8 bigger brother same contruction. I know different boat, different drive, props etc. But just looking at idle vacuum is the same. You were probably right not every engine is the same and not everything what mercruiser prints in service manual is applicable (that's not good BTW). I can only see that my engine runs reacher from 3000rpm (o2 target) and runs out of breath sooner at 4400 MAP = BARO, and PCM retards spark advance sooner. More fuel consumption probably dictated by vacuum dropping down sooner than it should in healthy engine. Seems that im back to square one. Overloaded or worn out engine? Strange with good compression. I will check the drive at some point.
I will also install new battery this week and run Diacom logs again.

My guess is that vacuum changing fuel pressure by about 10% isn't going to change GPH by 30%. Excessive fuel use is a symptom, not a cause.
If you are worried about fuel pressure, I recommend you follow the troubleshooting chart T-3 in section 1D of the engine service manual.
If the engine is in closed loop, the PCM will decrease fuel trims based on O2 feedback. I honestly don't think a few PSI to soon will have the effect your seeing.

From the manual

It is important to note that CDS G3... (Diacom in this case)
a. Does not indicate low fuel pressure. The PCM assumes that the pressure in the fuel rail is held at the specified pressure. If CDS G3 indicates a lean running engine, and the fuel injectors appear to be working, check the pressure in the fuel rail.
b. Does not detect poor fuel. As blended fuel ages, the alcohol and gasoline may separate and allow water to be introduced. The PCM will try to compensate for poor fuel by keeping the fuel injectors open longer. If it tries to add too
much fuel, it will trigger a fault. Even if it does not trigger a fault, bad fuel can result in a poor‑running engine. A small tank of known good fuel can be an important diagnostic tool.
c. Cannot determine the mechanical health of the engine. Always confirm the health of the cylinders by performing a leakdown test after confirming that all cylinders are receiving fuel and spark. Refer to the appropriate engine service
manual.

I can not stress enough that you should try running this engine on a small tank of known good fuel. EVERY shop I have ever worked in would have done this by now. This is a real easy test to preform. And a very important test.

I'm not sure about doing further diagnostics with low sea water pressure reading. The PCM monitors this and adjusts things based on the readings. I don't know to what extent this is done on your engine.

 

[muc]

My money is still on.
propping
starting voltage
fuel

 

[damo79]

My money is still on.
propping
starting voltage
fuel

Dropped prop by 1" already and didn't notice much difference and GPH stayed at the same level when cruising at 3000 or 4000rpm.

Is it possible that drive bearings are seized or maybe been replaced assembled bit too tight? Any way to verify that? Didn't notice anything when checking drive before summer. Spun shaft by hand with no extra force. But at high speeds its probably different.

According to Rinda tech support grayed out buttons its ECM's not Diacom limitation. Is it possible that PCM disabled them due to voltage issue during start up? Will find out tomorrow anyway with new battery.

 

[muc]

I thought you said you dropped 2” in pitch?
Generally speaking, a little boat like this, that should have a 19” prop will become a dog if you put a 21p on it. And will become a rocket ship with a 17p. 4” change will make a huge difference.

The drive, yes any good tech can feel tight backlash or rolling torque once the drive is off the boat, split into half’s and the impeller removed.
I would lean to bad engine alignment being more likely.

Rinda, yes, grayed out means MerCruiser isn’t allowing them to run this test. Probably because this engine doesn’t have a cam sensor, so the PCM doesn’t know what cylinder in the firing order is actually firing at any moment.

 

[muc]

Something else just popped into my head. I have very little experience with non OEM props.
You have a non Mercury prop. I don’t sell them, don’t use them and have never been in a situation where Mercury didn’t have the best prop for a Mercury application. They aren’t the cheapest but I do believe they have the most value.
You might want to contact the manufacturer of your prop. Tell them Mercury shipped this boat with a 19p Black Max when it was new, but you have never ran the boat with that prop. Give them ALL the RPMs and MPHs, at all the different speeds and what your WOT RPM is with the prop you now have on the boat. Ask for their recommendation.

 

[muc]

Another thing. Do you have the HIN and serial numbers for the drive and transom? With those I might be able to see how this boat came from the factory and what engine was in it then.

 

[Scott06]

I thought you said you dropped 2” in pitch?
Generally speaking, a little boat like this, that should have a 19” prop will become a dog if you put a 21p on it. And will become a rocket ship with a 17p. 4” change will make a huge difference.

Thanks for sharing your experience on this thread - 100% Agreed on the prop pitch. Most folks think taxing the engine less by going higher pitch/lower rpm and its the opposite. I have propped all my boats so lightly loaded I can tap the rev limiter trimmed up and WOT. Not that you have to drive WOT all day, but the boat will perform better and have great midrange throttle response if you do.

Went through this with my neighbors Lasron 2 summers ago- 21 ft BR with VP 220hp 4.3 mpi, SX drive 19" 3 blade AL VP prop. She is an avid waterskiier and thought her boat didnt have as much holeshot anymore. So took a look found the flame arrestor was caked with fuzz and that may have helped but she was only getting 4200-4300 at WOT. Suggested a VP 4 blade w 17" pitch - what a difference amd was hitting 4800-4900 WOT. Basically the dealer never set it up right.

Conversely another neighbor bought a new 2025 4winns Freedom H1 this spring with the 200hp 4.5 A1 combo. I had hesitation about him not getting the 250 hp model in a 21 ft, but he was trying to hit a price point. I told him when he takes delivery to make sure what ever prop they had on it will hit 4800 WOT. I expected them to have a black max or vengence prop on it. They already set him up with a 19" Revolution 4 and it pops up on a plane towing a slalom skiier with 5 people in the boat, and hits 4800. In this case the dealer did their homework and set it up perfectly, shows what you can do with the correct prop, easily gives my similar size 260 hp/5.0 sea ray a run for its money

 

[damo79]

I thought you said you dropped 2” in pitch?
Generally speaking, a little boat like this, that should have a 19” prop will become a dog if you put a 21p on it. And will become a rocket ship with a 17p. 4” change will make a huge difference.

The drive, yes any good tech can feel tight backlash or rolling torque once the drive is off the boat, split into half’s and the impeller removed.
I would lean to bad engine alignment being more likely.

Rinda, yes, grayed out means MerCruiser isn’t allowing them to run this test. Probably because this engine doesn’t have a cam sensor, so the PCM doesn’t know what cylinder in the firing order is actually firing at any moment.

Sorry my bad it was 2" from 14.25x19" Turning Point 2150211 that was on the boat to 14.5x19 SS Balistic

Michigan Ballistic 3-Blade Prop, SS 14.5x19 LH Hub

Discover the Michigan Ballistic 3-Blade Prop with exchangeable hub. Stainless steel, 14.5" dia x 19" LH. Perfect for enhancing your boating experience.

www.overtons.com

I will check HIN and get back to you

 

[Scott06]

Sorry my bad it was 2" from 14.25x19" Turning Point 2150211 that was on the boat to 14.5x19 SS Balistic

Michigan Ballistic 3-Blade Prop, SS 14.5x19 LH Hub

Discover the Michigan Ballistic 3-Blade Prop with exchangeable hub. Stainless steel, 14.5" dia x 19" LH. Perfect for enhancing your boating experience.

www.overtons.com

I will check HIN and get back to you

?? you went from a 19" pitch to another 19" pitch based off the what you just posted.

if I recall from here the ballistic props are hit or miss on a particular boat. if I recall it has the clipped ends to the blades? try a 17 it may be cheapest part of the parts cannon.

 

[damo79]

?? you went from a 19" pitch to another 19" pitch based off the what you just posted.

if I recall from here the ballistic props are hit or miss on a particular boat. if I recall it has the clipped ends to the blades? try a 17 it may be cheapest part of the parts cannon.

Typo - my bad again Turning Point was 14.25x21". And yes Ballistic has clipped blade ends.

 

[damo79]

Another thing. Do you have the HIN and serial numbers for the drive and transom? With those I might be able to see how this boat came from the factory and what engine was in it then.

Never thought about that. Asked Bayliner and that's the info I got. Replaced battery but the weather wasn't good enough to run ang tests with diacom.

 

[muc]

Thanks, non of these have been registered with Merc.
Drive is listed as 1.62:1 ratio when it left the factory.