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

[damo79]

@muc I also checked fuel supply module and it works nearly as it sholud. 1st video - ignition on the pressure goes up to 51psi. Then at idle stays steady 46psi. According to manual it should be 40-45. Its 1psi above acceptable range because its regulated by vacuum pressure and if this is too low fuel pressure will be too high. Second video - vacuum line disconnected from FSM and it stays at 52psi. Then you see the drop but it was me sucking air out of the hose connected to fuel module. So it will come down to 40-45psi once vaccum pressure will be within range of 17-21psi. As you can see from Diacom files with engine warmed up it never was more than 13psi at idle.

 

[damo79]

Can we now all agree that low vacuum is what I should be sorting out first?

Today checked intake manifold with smoke generator. No leaks

Any other ideas what to check?

 

[muc]

@muc please see the attached Diacom recordings. The engine stopped due to an alarm, so the log is split into two files. Hope this is sufficient.

What was the alarm?

 

[Captain of the Double G's]

Uhm, sorry to sound naive but have you checked the actual fuel quality and
actual octane content. Maybe a tank of high test ? Sometimes we forget the obvious.
Also, are you running the correct spark plugs the manufacturer recommends ?
Believe it or not...it makes a difference.

 

[damo79]

What was the alarm?

Not sure because nothing showed up on Diacom. Guessing low water pressure

 

[damo79]

Uhm, sorry to sound naive but have you checked the actual fuel quality and
actual octane content. Maybe a tank of high test ? Sometimes we forget the obvious.
Also, are you running the correct spark plugs the manufacturer recommends ?
Believe it or not...it makes a difference.

Fuel quality causing low intake vacuum? Its 95 octane exactly name E10.
Spark plugs are correct.

 

[damo79]

@muc what do you think of oil pressure?

Only min oil pressure is specified in service manual 41kPa, mine is 280 at idle and 330 at 3000rpm. I'm just wondering if excessive oil pressure could be causing hydraulic lifter pump-up which in turn keeps the valves slightly open preventing the engine from creating proper vacuum?

 

[tpenfield]

Now that I am an outboard guy, my knowledge on the Mercruiser front is quickly fading . . . but just taking a look at the data, a thought that came to mind was the throttle plate. (loose, linkage, something.)

 

[damo79]

Now that I am an outboard guy, my knowledge on the Mercruiser front is quickly fading . . . but just taking a look at the data, a thought that came to mind was the throttle plate. (loose, linkage, something.)

There's only the potmeter on shift plate and it sends signal to PCM and PCM controls the throttle body (drive by wire). Is that what you asked for ?

 

[Captain of the Double G's]

I have seen throttle plate bores leak at the pivot points. spray some brake
cleaner while running to verify if any change in rpm. A leak there would be sort of internal vacuum leak causing the computer to "change things" lol ?
Thinking about it a manifold gasket could also do it.

 

[damo79]

I have seen throttle plate bores leak at the pivot points. spray some brake
cleaner while running to verify if any change in rpm. A leak there would be sort of internal vacuum leak causing the computer to "change things" lol ?
Thinking about it a manifold gasket could also do it.

Tried that while ago no leaks. Sprayed everywhere around intake and injectors. And this PCM wont change rpm even if sprayed engine starter into throttle body - tested to see reaction. Noticed only fuel consumption going gown immediately on vessel view.
Checked also with smoke generator no leaks.

 

[Captain of the Double G's]

Some thoughts, you smoke tested but did you remove dipstick to check for internal leak ? Old fashioned timing light to check chain stretch ?
Secondary valve spring broken ? CORRECT throttle body ? Updated
ecu program for that motor ? Fuel consumption went down on view because some of that spray almost had to go into intake. CORRECT intake ?
Really sounds like internal vacuum leak ( maybe intake gasket ? ) that would make the computer ramp up fuel volume causing increase in fuel consumption.
Also 14.7v at idle seems on the verge of being too high ? Computer adjusting for high voltage ? Partial exhaust restriction ?
Happy Hunting !

 

[damo79]

Some thoughts, you smoke tested but did you remove dipstick to check for internal leak ? Old fashioned timing light to check chain stretch ?
Secondary valve spring broken ? CORRECT throttle body ? Updated
ecu program for that motor ? Fuel consumption went down on view because some of that spray almost had to go into intake. CORRECT intake ?
Really sounds like internal vacuum leak ( maybe intake gasket ? ) that would make the computer ramp up fuel volume causing increase in fuel consumption.
Also 14.7v at idle seems on the verge of being too high ? Computer adjusting for high voltage ? Partial exhaust restriction ?
Happy Hunting !

Yes I did remove oil cap - no smoke there.

Did not check timing old fashion but will it work if PCM controls timing and shows already -3 deg at idle?

Broken valve spring - don't think so compression 180psi each cylinder.

I will definitely remove intake and check valve springs and clean hydraulic lifters, gaskets etc, but that after summer. I've got still two weeks in marina and then will take boat on trailer.

Exhaust checked no restrictions.

14.7V but all sensors getting correct 5V.

I know that PCM can double injector pulse time if vaccum is incorrect - see once more attached ECM555 logic. I believe PCM112 works similar way.
Vaccum is way off at idle and I hope I will find the reason.

 

[Scott06]

I will definitely remove intake and check valve springs and clean hydraulic lifters, gaskets etc, but that after summer. I've got still two weeks in marina and then will take boat on trailer.

Exhaust checked no restrictions.

I wouldn't be pulling the intake at this point nothing points to that if there is no vacuum leak at the gaskets.

you have low vacuum at idle but the idle rpm is normal? I assume there is something like a IAC valve that regulates idle RPM what is that doing? if closed all the way and still idling that would make me think that could be an issue but doesnt point to overall power issue

 

[damo79]

I wouldn't be pulling the intake at this point nothing points to that if there is no vacuum leak at the gaskets.

you have low vacuum at idle but the idle rpm is normal? I assume there is something like a IAC valve that regulates idle RPM what is that doing? if closed all the way and still idling that would make me think that could be an issue but doesnt point to overall power issue

Thats correct. Not sure what's the logic of this PCM. Speed and density controlled. There is no IAC just throttle drive by wire. Guessing that PCM calculates air density from vacuum and temperature (TMAP sensor) and adjusts injector pulses to keep stichometrtic ratio. How does the RPM stay steady at idle with low vacuum IDK maybe controlled with timing?
Reason I want to pull the intake is to check valve lifters. But that after few more checks before that.

 

[Captain of the Double G's]

OK, more thoughts, a secondary valve spring should only be a factor at higher rpm. Some of the timing readings seem off ? Should be ( my old memory here, first to go, second I forgot ) should be 5-15% at idle ( forum feel free to verify ) .
My new thought is finding a way to check your map ( tmap) hz reading at idle, typical regular map readings are 57hz +/- 3 at sea level. ( i.e. 144hz would be 10k feet ) Flow reading could be ok and still think its on a mountain or 300 ft deep.
Your water temp is 32F, I assume you are not using that system, and it may not matter, I just remember "sort of" 32 is default , IDK.
Also I have had many problems with aftermarket( and sometimes factory) "Brand New" sensors in my 45 years repairing cars ( and old inboards ). If it were me I would replace the sensor again first( after having computer reflashed, should be done anyway ) since your engine only has 600 hours ( yes I know, not much for a car , marine X a factor of ?...really want to know forum people ).
Other than that base engine or ECM problem, ECM is expensive guess.
Last, this is a repower ? Does it have an aggressive replacement camshaft ?
Happy Hunting

 

[damo79]

I'm not sure what timing should be as well as other things that's why started this post and asked for help with checking Diacom data.
TMAP was verified - diacom readings vs physical gauge. Both show the same.
Not sure why sea water temp is always 32F.
This engine its Mercruiser own design and don't think that ECM reflash or checkum verify will be that easy. Heard before that only option here in Europe is to ship it to Belgium to Mercruiser

 

[Captain of the Double G's]

That engine should be 5-15% at idle.
Change that sensor, at worst you will have a spare on board ( not a bad thing )

 

[muc]

Can we now all agree that low vacuum is what I should be sorting out first?

NO.
I keep saying these MAP readings are normal.
While I don't have any other 4.5 Diacom REC files to compare (I have always used Mercs G3 on these engines because I'm at a dealer and I now work the parts counter and no longer have access to G3) but, I do have a bunch of Diacom REC files for similar engines. When I look at ANY of those files All of them have MAP readings at idle that are the same or lower. This engine has an Electronic Throttle Body O2 sensors and Adaptive Speed Control (ASC) it isn't the same (or really even comparable) to a carb, Throttle Body injection or even a MPI 555 engine. I don't know where you're getting this 17-22 number from, but it's not from Merc or someone who is familiar with these latest generation engines.

I've had a chance to review the 2 newest REC files you posted. Not a lot of diagnostic data in them because of how you were operating the throttle.
Maybe I should have been clearer about how to make a REC file.

"Run around until engine reaches complete warm up."
This will take 15-30 minutes depending on a few things, sea water temp, cooling poppet spring tension, hull weight/design, etc.
This will answer your oil pressure question - it wasn't fully up to temp, so it will read a little high. But those oil pressure readings you're seeing are normal. You also asked about the sea water temp reading - you don't have that sensor, so 32° is there because it's the default number Merc programmed in the PCM.

"Now back to idle and then increase RPMs in 500 RPM increments holding steady at each for 5 minutes."
This should take about one hour, you can shave the 5 mins to 3 mins if you don't have the time. The 2 REC files you posted are only about 15 mins total, so like I said -- not much usable data. If you're wondering what I'm talking about, just graph "O2 Control State" and "RPM / Load State" do you see how they're jumping all over the place? Nobody can get solid diagnostic numbers when this is happening.

But I am able to some things wrong.

Sea Water pressure, impeller, sensor, wiring or something else in the cooling system. This needs to be addressed, The PCM112 monitors this number and adjusts different things due to the low numbers. So it will affect what different tables like spark, fuel, VE (volumetric), ER (equivalency ratio) the PCM uses.

Trim sender is jumping all over. It even told the PCM you were in trailer mode a couple of times. I'm not sure how much of this the PCM looks at or adjusts tables because of, or even what the countdown timer is for this data point. So I can't say for sure if you need to replace the sender/troubleshoot the wiring like I can for the sea water pressure and the biggest thing I saw in the files, up next.

You have a bad battery and/or wiring issues. The PCM is seeing about 8.5 volts on the Battery volts and just a little higher on System volts. This is REALLY bad and will cause all sorts of weird issues. I haven't seen MerCruiser post a number for the PCM, but 10.5v was considered bad with the 555 and Mercury does post a number for the outboards with the PCM112 and that is 11.5 v. So your boat is way low.

I'll take look at some of your other questions and see if I can answer them.

 

[muc]

That engine should be 5-15% at idle.

What should be 5-15%?