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

[muc]

Cam Lobe Lift looks right. But as far as the other measurements --- I have no idea. Mercury doesn't publish any of these numbers. Also I don't know if I would trust that the TDC that you're going off of is correct. The outer ring that's marked with TDC can be off. They can slip a little. The only way I know how to check this is with a dial indicator on the top of the piston #1 or #4, rotating the crankshaft clockwise and stopping about 3-4mm before TDC, mark the balancer and then rotate crank counterclockwise and stop at the exact measurement as before, mark balancer and then split the difference to determine true TDC. I'm not sure this could be done with the cylinder head still bolted on (I've never tried it). This is how it's done with the old 2 stroke outboards, but they have the plug hole pointed straight at the piston. Maybe someone reading this has and could speak up? I'm also not 100% sure this would be necessary to determine if the timing chain jumped a tooth.

You might try calling the consumer support number I posted earlier, maybe they can help with the cam timing questions? Or maybe someone has posted cam specs that might apply to your engine. I'm unable to help with these questions. About 30 years ago I stopped spending my or other peoples money chasing more horsepower. I learned that if you want a faster boat --- buy a faster boat, after good propping and a few minor bolt on things --- it's usually cheaper and better.

I will be very interested to see what happens once this is back together and over revved to see what happens.

 

[damo79]

TDC was correct confirmed with inspection camera. First set best what I saw on camera and then checked TDC.
Emailed Merc but seems that they wont tell anything more than is in service manual or published in bulletin. They told me what should be fuel pressure but nothing about vacuum or cam timing measurements. They suggested to run leak down test and get Merc dealer to perform G3 checks and proper propping procedure.

Checked that procedure and according to that and previous diacom reading I have to drop prop pitch.

https://share.google/B2qjmEAuPKKlZhSCa

 

[muc]

Yes, I didn't think Merc would help you much but I was hoping they might be willing to help due to you being in the EU.
They always ask for a leak down test. If I feel one might needed I will usually do a "dynamic compression test" instead. On these I/O engine I find they are just as informative and way faster and easier.

Suggest you try a Merc Black Max 15X17" p/n 832828A45 it will come with the hub kit for $267.06 US

This is based on what I have seen in the REC files.

 

[muc]

I just looked up your Ballistic prop. I'm surprised someone would recommend this prop for your application.
Looks like the Ballistic uses the same hub system. If it's exactly the same you could look for a Quicksilver brand prop. It's the same as the Black Max but called Black Diamond and doesn't come with the hub kit, so a little cheaper.
p/n QA1912X $192.38 US

 

[damo79]

I read more about props I have. Asked AI to compare them both and find Black Max equivalent. No wonder dropping prop pitch by 2" didn't change much. 19" and 21" I have are pretty much the same - equivalent to 21.5-22" Black Max.
What about trying 14.5x19" Black Max - that's standard for this boat with 250HP merc and 1.62 alpha one drive?



I tested the engine without drive installed and water connected directly to the hose behind transom. The engine reved to 5400rpm. What I also noticed in Diacom during that test that engine vacuum was 15-16inHg (12.5-13 with drive installed) and fuel consumption dropped at idle by 25-30%. Isn't that difference to much just to move drive shafts and gears. Maybe I have combination of wrong propping and to much friction somewhere - drive or transom?

 

[damo79]

I also performed leak down test. First the cold engine readings were 25-32%.
Then yesterday after waming up the engine and checking the engine max rev. At TDC worse cylinder improved from 32% to 25%, the rest show the same 5-7% improvement. Not to good anyway? Not sure what are good readings for marine engine. With an inspection camera I noticed that one valve didn't look fully closed. Moved from 0° to 10° and leak down test improved from and got 12-15% on each cylinder but had to move each pair approx 10°past TDC. Is it normal or do I have hung valves at TDC. That 10° is like 2mm on cylinder movement.

 

[tpenfield]

Reving an engine under no load conditions does not prove anything, except maybe where your rev-limiter is at.

10˚ past TDC for leak test is OK, but it is interesting that the 'bad' cylinder was leaking at TDC. Maybe (if you can) see if you can take leak % on that cylinder throughout the compression and power stokes.

 

[muc]

I would NEVER pay any attention to AI when it comes to propping! It is getting it's information by scraping everything it finds. It doesn't know the difference between facts and someone in one of these forums who is so confidently so incorrect.

Try whatever prop you want. I recommended the prop I did for a few reasons.
It's a Mercury, that's the best anyone can do when buying a basic prop.
Your current WOT RPM say's go to17p
Your engine will always be happier under propped then it will over propped.
When I watch the REC files, it looks like to me that where your boating doesn't allow you to run WOT for very long without steering, trimming or adjusting the throttle. If you're not looking for the boat to go as fast as it possibly can ---- always under prop with these new computer controlled engines.

Don't pay any attention to the vacuum or fuel flow while revving an engine in neutral, the PCM is doing soo many things trying to limit any damage you are trying to cause by free revving.

When you checked engine alignment, did you recheck it at 12:00, 3:00, 6:00 and 9:00? You should, regrease the part of the tool that goes into the spines. Grease marks should be close to the same at all 2 positions.

Did the engine go into RPM reduction @5400? Did it set a horn or code?

Where did you hear the air leaking out?
You need to listen 4 different places. Oil fill, Throttle body -- have to remove flame arrester and make sure throttle blade is open, exhaust and drain the cooling system and remove a hose from the crossover assy.
Your leak numbers look pretty bad to me.
but
I have to question the leak down results.
Merc wants this engine leak down tested @20-30psi. This is usually a decision a engine builder makes due to the pistons and rings they are using. Suggest you follow the service manual closely for procedure.
I'm guessing the tester your using is a 100psi style. I'm guessing it will still work as the new lower psi testers are something pretty recent. But you have to follow the instructions. If you are setting the left gauge to 100psi it should stay there when you connect to the cylinder, I'm told that if it doesn't --- means air compressor is undersized for this job.

I'm guessing something is wrong with the timing mark you're using, turning the engine to 10° ATDC should cause the engine to spin from the air pressure. Testing should be done ATDC. Or maybe you're on the exhaust stroke?
Something is wrong with your testing.

When posting it is best to post the actual numbers for each cylinder when doing a leak down or compression test. Sometimes someone with a lot of experience will see something with the numbers.

 

[damo79]

I referred to vacuum and fuel flow during idling for few minutes not revving. Vacuum is 3inHg lower and fuel consumption is 25-30% higher at idle with drive installed. That's why asked if that difference is something normal.

I didn't check engine alignment at 12, 3 etc. I will check that.

I didn't keep the engine at max rev long enough to get any horn warning or code but heard rev limiter.

I've noticed Merc wants leak down the engine at 20-30psi but they mention it as "additional test of low compression cylinders". I thought that the reason of that low test pressure was just to determine leak of already bad cylinder.

 

[muc]

Vac+fuel, yes if something else is different like coolant or air temp, exhaust back pressure, BARO or load. Expect it to change.

Where did you hear the air leaking out?

A leak down test is such a time consuming and difficult test to do properly that it is usually only done on cylinders that failed the compression test to determine if we are pulling the heads or pulling the engine.

Have you turned the u-joint shaft while the drive is in forward gear and counted how many turns it takes to get the propeller to turn 10 times?
This and trying a known good prop is the second step in the trouble shooting tree.

 

[damo79]

Is was leaking from valve cover vent.

Drive was checked for correct ratio and 1.62 was confirmed by turning u joint shaft 10 times and counting 6,2ish prop revs.

Is the specification showed below correct for the alignment tool? The I borrowed from a friend and it look like machined in the shop. Its spline end is a bit smaller in OD and it's not very precise. I never done it before but seems to much play inside the spline. Maybe its the wrong type. I can get next one machined if you can please confirm the size or order one (200USD here).

 

[muc]

Some air will always leak past the rings. That’s why it’s so important to do this test as I described, you are listening for how much air at the 4 places.
Remember that ANY test done incorrectly can result in incorrect conclusions.

I can’t help with dimensions, I only use OEM tools. I don’t think that a little variation in diameter would make much difference as long as you do the procedure correctly. Grease the end uniformly And mark the tool to make sure you don’t rotate it. Push it straight in and put a little pressure on it up, down, right, left. Pull it straight out and inspect the marks in the grease. Some techs will hit the tool on all 4 sides with a dead blow hammer because this can help show the grease marks and will also center the gimbal bearing.
There might be specs on this tool in the sticky section at the top of this forum.