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

[damo79]

@muc please see attached recent Diacom test run with new battery.
Old one wast tested and it was time to replace it. Capacity was still ok but cranking current only 480A. New one is 850A
Didn't notice any change in performance, still the same

 

[muc]

This wasn't the REC file I was hoping for.

Here is what I see.

Voltage still too low. this might explain the numbers I'm seeing and the many sensor spikes at unusual times.

Sea water pressure too low and has some of those spikes. Maybe this affecting the WOT? I'm not sure.

Fuel trims very high (very close to setting fault) at strange times and have a wider difference between port and stbd that what I'm used to seeing.
.
phi (equivalency in Diacom) both target and actual are much higher then normal. Also unusual spikes. From the manual "The difference between phi and DesiredPhi can indicate things such as fuel restriction, fuel quality, high fuel rail pressure, fuel injector failures"

It appears trim sensor is inop or you're not using the trim. Are you using trim? This makes it hard for me, I'm not there so I need to look at demand, demand linear, TPS, etc. to try and figure out what is happening with the steering wheel and waves. Can you tell me a little about this run. I can see you going in and out of gear (this is hard for me to interrupt because Diacom calls these switches by different names) then Merc does. Also many times you back off on the throttle before increasing it to get to the next RPM range. I'm not there so maybe water conditions?

When I look at the (little over a minute) WOT part of the file. I see you have the throttle 100%, the PCM is commanding 100%, but for some reason the TPS is slowly closing to 65%. I can see no reason for this to be happening anywhere in the REC file. It's very normal to see this at demand linear less then 100% because ACS is trying to keep a constant RPM, but not at WOT.

I have some questions.
Have you replaced O2 sensors? If so, did you use OEM?
Have you dumped the fuel filter into a clear and clean glass to inspect? Have you replaced the filter element?
Have you tried running the engine on a different fuel tank filled with the best gas you can buy?
Do you have a picture of the stickers on the PCM?

Next time you do another Diacom run, you should trim up far enough to blow out the prop at WOT. It might help to see what happens when you hit the rev limiter. Don't worry about over reving the engine, the PCM is way to smart to let anything bad happen.

So to sum up, I can see why you can't get over 4500, I just don't know why.

 

[muc]

Seems strange that Bayliner states that boat was sold with engine currently installed and you found out that thia engine was warranty return sold on Merc auction in 2018.

Yes I have never seen this before. Maybe a EU thing? Engine build date 2016 sold in 2018. I'm not sure about it being a warranty return, just that the engine only was registered by the warranty dept.

 

[damo79]

This wasn't the REC file I was hoping for.

Here is what I see.

Voltage still too low. this might explain the numbers I'm seeing and the many sensor spikes at unusual times.

Sea water pressure too low and has some of those spikes. Maybe this affecting the WOT? I'm not sure.

Fuel trims very high (very close to setting fault) at strange times and have a wider difference between port and stbd that what I'm used to seeing.
.
phi (equivalency in Diacom) both target and actual are much higher then normal. Also unusual spikes. From the manual "The difference between phi and DesiredPhi can indicate things such as fuel restriction, fuel quality, high fuel rail pressure, fuel injector failures"

It appears trim sensor is inop or you're not using the trim. Are you using trim? This makes it hard for me, I'm not there so I need to look at demand, demand linear, TPS, etc. to try and figure out what is happening with the steering wheel and waves. Can you tell me a little about this run. I can see you going in and out of gear (this is hard for me to interrupt because Diacom calls these switches by different names) then Merc does. Also many times you back off on the throttle before increasing it to get to the next RPM range. I'm not there so maybe water conditions?

When I look at the (little over a minute) WOT part of the file. I see you have the throttle 100%, the PCM is commanding 100%, but for some reason the TPS is slowly closing to 65%. I can see no reason for this to be happening anywhere in the REC file. It's very normal to see this at demand linear less then 100% because ACS is trying to keep a constant RPM, but not at WOT.

I have some questions.
Have you replaced O2 sensors? If so, did you use OEM?
Have you dumped the fuel filter into a clear and clean glass to inspect? Have you replaced the filter element?
Have you tried running the engine on a different fuel tank filled with the best gas you can buy?
Do you have a picture of the stickers on the PCM?

Next time you do another Diacom run, you should trim up far enough to blow out the prop at WOT. It might help to see what happens when you hit the rev limiter. Don't worry about over reving the engine, the PCM is way to smart to let anything bad happen.

So to sum up, I can see why you can't get over 4500, I just don't know why.

System voltage still drops to 10.2V. Checked @tpenfield files and both his V8 engines do the same while cranking. Maybe that's normal.

Sea water pressue been an issue from the time it suddenly dropped and stayed like that (maybe 2 weeks). I will check that this week. Maybe its just he sensor - water temp stays within the range.

What do you mean by very high fuel trims? They stay within 2-5% while on steady rpm and spikes are during acceleration and slowing down from WOT is the biggest spike -14% but only few seconds.
I agree that port is always -2..4% and stbd +2...4% not sure what sould it be.
Phi - did you mean Equiv Ratio Target?

I use the trim only to the point when I hear prop ventilating and then back of a little. TBH this boat doesn't need much triming that's why you dont see much trim movement.

About the run - first few part up to 3000rpm I was hitting small vawes going downwind. Also trimed down to stop boat pounding. After that when rpm was 3400 and above it was calm and the moments you see me slowing down before going up to next rpm level I was taking turns to try keep the boat in sheltered water.

Without trim at WOT max was 4350rpm and when I trimmed up a little and had a feeling that I only gained rpm from 4350 to 4500 but not speed maybe that's why TPS went down.

 

[damo79]

O2 sensor was replaced with new one. Before I got Diacom, the engine was checked by a marine tech and the only think he told me was that o2 needed to be repleced, because reading stays at the same level all the time.

Little backstory about Bosch sensor. The original one was BOSCH 0258017 244. Its was imposible to buy this specific one - discontinued according to Bosch or what I suspect reserved for Merc, Volvo Penta and John Deere. The OEM Merc was not available in Poland and delivery time was 2-3 weeks. So I contacted Bosch and they recommended 0258017 025. According to and email i received from Bosch , it is the same sensor just with different cable lenght.

I never run the boat from separated tank. I used few tanks of fuel this season and didnt notice any improvement. Fuel filter was replaced before season.

​

 

[damo79]

@muc Please take a look at my recent Diacom test run. I did it using an external fuel tank. It was mailny test of WOT and playing with the trim.
Conditions - flat calm, no wind. First run at 3000rpm to see what speed I'm getting on gps - it was 26mph.
Steady plane at 3000rpm then trimmed up to 10% until it started ventilating. You will notice that engine load changed from 60% to 48% but that just because trimmed to much. Checked speed at 3450rpm - 29mph.
Then slowed down stopped and quick start to WOT. With optimal trim hit 4300rpm and 39mph. This was max I can get of that boat. Then took your advice and trimmed up more to see if it will hit rev limiter. Speed stayed at 39mph revs went up to 3750rpm. You will notice trim going from 10-25% and back but it was me trying to get control over the boat. Water was spraying behind, trim up till the point that boat started turning itself and had to came down on trim again. So with optimal trim it hits 4300-4400 and 39mph. Rest you see its prop ventilating to the point that there is no control over the boat.
TBH I got a feeling after this test that this engine wouldn't hit 5000-5200rpm with prop removed.

After that came back to marina and reconnected fuel line to the tank and tested it again. No change 39mph is max at 4350ish and 4750rpm with trim up to 25% but no change on speed.

 

[muc]

I don't have the time right now to spend the time I need, hopefully tonight or tomorrow.
I do have a couple of questions for @tpenfield. Ted, I can't remember but back when you made these REC files for your MerCruisers, weren't you trying to troubleshoot a low voltage alarm? Also I can't find any files from you that have a cold start or WOT in them. Would it be possible for you to send them to me? Or could you give @damo79 permission to send them to me?
Thanks

 

[tpenfield]

I don't have the time right now to spend the time I need, hopefully tonight or tomorrow.
I do have a couple of questions for @tpenfield. Ted, I can't remember but back when you made these REC files for your MerCruisers, weren't you trying to troubleshoot a low voltage alarm? Also I can't find any files from you that have a cold start or WOT in them. Would it be possible for you to send them to me? Or could you give @damo79 permission to send them to me?
Thanks

I believe those files were from when I was having EMCT overheat issues.

IIRC, I solved the voltage issues in 2022.

There was an electrical issue with the engines apparently sharing voltage, but I’m not sure I ran any Diacom files, since the boat was on land at the time.

 

[muc]

TBH I got a feeling after this test that this engine wouldn't hit 5000-5200rpm with prop removed.

That's where I would go next. I think it's very important to answer this question.
Try in neutral and see if you get a Neutral Overspeed fault, this should show a fault on your VV screen and Guardian in Diacom.
If you want test without pulling the prop, you can trigger or bypass the in gear switch --- Diacom appears to call this Actual Gear. Or maybe remove the inner transom shift cable so the prop doesn't engage. Should see Guardian Overspeed fault. Let it spend 5-10 seconds on the rev limiter.

Your replaced O2 sensors, did you install them unmodified? No replacing the connector, wires modification or dielectric grease? I always get worried by non OEM parts. Very important for O2 sensors. Dealer I work at fix's quite a few motors just by replacing non OEM parts that the customer or some other service provider installed.

I haven't had the time to spend the time I need to look at the REC files. But when I look at 8/17/26 19:31:18.887 I see everything at 100% for about 3 seconds with trim at 10% then while RPMs are still climbing trim drops back to 0% @ 19:31:23.539 before trim starts going up to 30% and I assume that when the prop is ventilating.
When I look at 8/16/26 file i see only about 1.5 seconds at WOT at 0% trim.
When I look at 8/4/26 files I see only 3-4 seconds at WOT at 7 and 10% trim.
I think you need to let it go longer.
Am I misreading the times?

Can you do another REC file with more time at WOT? Full throttle and slowly work the trim up and down. I would like to see 4-5 minutes.

 

[tpenfield]

I don't have the time right now to spend the time I need, hopefully tonight or tomorrow.
I do have a couple of questions for @tpenfield. Ted, I can't remember but back when you made these REC files for your MerCruisers, weren't you trying to troubleshoot a low voltage alarm? Also I can't find any files from you that have a cold start or WOT in them. Would it be possible for you to send them to me? Or could you give @damo79 permission to send them to me?
Thanks

I have no issue with sharing my Diacom files . . . @muc @damo79

 

[damo79]

That's where I would go next. I think it's very important to answer this question.
Try in neutral and see if you get a Neutral Overspeed fault, this should show a fault on your VV screen and Guardian in Diacom.
If you want test without pulling the prop, you can trigger or bypass the in gear switch --- Diacom appears to call this Actual Gear. Or maybe remove the inner transom shift cable so the prop doesn't engage. Should see Guardian Overspeed fault. Let it spend 5-10 seconds on the rev limiter.

Your replaced O2 sensors, did you install them unmodified? No replacing the connector, wires modification or dielectric grease? I always get worried by non OEM parts. Very important for O2 sensors. Dealer I work at fix's quite a few motors just by replacing non OEM parts that the customer or some other service provider installed.

I haven't had the time to spend the time I need to look at the REC files. But when I look at 8/17/26 19:31:18.887 I see everything at 100% for about 3 seconds with trim at 10% then while RPMs are still climbing trim drops back to 0% @ 19:31:23.539 before trim starts going up to 30% and I assume that when the prop is ventilating.
When I look at 8/16/26 file i see only about 1.5 seconds at WOT at 0% trim.
When I look at 8/4/26 files I see only 3-4 seconds at WOT at 7 and 10% trim.
I think you need to let it go longer.
Am I misreading the times?

Can you do another REC file with more time at WOT? Full throttle and slowly work the trim up and down. I would like to see 4-5 minutes.

Unfortunately the boat is back on trailer, my 2 paid months in local marina are over. Wish I tried that test on idle when the boat was still in the water. Any suggestions what I can check when on trailer - engine, drive?
I already took the drive out and checked ratio 1.62 by rotating the shaft you asked before. Gimbal bearing looks and feels fine same as engine alignment checked with tool greased at the end. Before the season the drive went in easy and came out easy. I didn't feel any extra resistance when spinning the shaft. But that my second boad - previously own Volvo penta with sx drive so hard to compare. When impeller was removed it spun very easy so probably only resistance was the impeller itself inside housing. Checked water pump and impeller and only one reason of low watter pressure found so far is marine growth in water holes and inside the drive. See pictures.

I will look at Diacom and try to answer your questions later.

O2 original sensor was Bosch as mentioned earlier and replaced with what Bosch recommended as previous one is discontinued. Buying Bosch sensor from Merc is just the same packed in their bag and costs 3 times more. But for me it was more availability in Europe. Finally only one o2 sensor was faulty still have one original swapped them with sides and made no difference on Diacom so I assume that thta one replaced is new. No wires modification just replacement.

 

[muc]

Looking at the pics. Bearings and gears look pretty good. Yes you should clean the water passages! Here in the US we use toilet bowl cleaner, not sure what you have available in the EU. Might need to use muriatic acid for swimming pools? Hard to tell from pics but the gear lube worries me a bit, looks like it might have some water or aeration in it. Doesn't look like the OEM lube.

Do you have access to a water hose with enough volume where the boat is now. It doesn't much matter in the water or out to over rev the engine for the test we need next.

 

[damo79]

Looking at the pics. Bearings and gears look pretty good. Yes you should clean the water passages! Here in the US we use toilet bowl cleaner, not sure what you have available in the EU. Might need to use muriatic acid for swimming pools? Hard to tell from pics but the gear lube worries me a bit, looks like it might have some water or aeration in it. Doesn't look like the OEM lube.

Do you have access to a water hose with enough volume where the boat is now. It doesn't much matter in the water or out to over rev the engine for the test we need next.

Looking at the pics. Bearings and gears look pretty good. Yes you should clean the water passages! Here in the US we use toilet bowl cleaner, not sure what you have available in the EU. Might need to use muriatic acid for swimming pools? Hard to tell from pics but the gear lube worries me a bit, looks like it might have some water or aeration in it. Doesn't look like the OEM lube.

Do you have access to a water hose with enough volume where the boat is now. It doesn't much matter in the water or out to over rev the engine for the test we need next.

It's not OEM lube its Motul Translube Expert 75W-90.

I have garden hose and earmuffs I normaly use to run the engine to operating temperature and flush it after used in salt water. The boat is just next to my garage. I thought that I can run only on idle when water is supplied from earmuffs. Not sure what volume is enough to max rev the engine.

 

[damo79]

Looking at the pics. Bearings and gears look pretty good. Yes you should clean the water passages! Here in the US we use toilet bowl cleaner, not sure what you have available in the EU. Might need to use muriatic acid for swimming pools? Hard to tell from pics but the gear lube worries me a bit, looks like it might have some water or aeration in it. Doesn't look like the OEM lube.

Do you have access to a water hose with enough volume where the boat is now. It doesn't much matter in the water or out to over rev the engine for the test we need next.

 

[damo79]

I checked what you asked for with Diacom recording. Checked graphs, looking at demand, rpm and trim. From what I can tell optimal max trim for WOT is 5%. Anything above that causes only rev increase but speed on gps does not change. That's why on previous recordings you noticed quickly going up and down. As soon I heard ventilation I took it down.

 

[damo79]

In post #149 you mentioned that maybe I have overloaded engine - wrong prop, gear ratio, engine misalignment. Is it anything else I can check with drive?

Also warn out or damaged engine was mentioned. What should I look for?
I removed spark plugs, checked them and did compression test again and got 180psi on each cylinder, cold engine 4 pufs.
Also took out exhaust manifolds for inspection and to get access to inspect valve rockers and springs.
Is it any way I can check timing without removing timing chain cover?
IDK maybe with dial gauge checking valves vs cylinder movements?

 

[muc]

It's not OEM lube its Motul Translube Expert 75W-90.

I have garden hose and earmuffs I normaly use to run the engine to operating temperature and flush it after used in salt water. The boat is just next to my garage. I thought that I can run only on idle when water is supplied from earmuffs. Not sure what volume is enough to max rev the engine.

I just mentioned the gear lube because it didn't look like what I'm used to seeing, I can't say if it will cause you issues. It appears to meet Merc specs. I'm pretty sure it isn't causing your current issue.

Mercury recommends that customers don't exceed 1500 RPMs on muffs. They want you to take it to a trained professional. We do this all the time when needed. Here is how you do it, install muffs and turn water on full, note how much water is escaping around the muffs, start engine and note there is less water escaping. You can keep increasing engine speed until you reach the point of NO water escaping.

 

[muc]

I checked what you asked for with Diacom recording. Checked graphs, looking at demand, rpm and trim. From what I can tell optimal max trim for WOT is 5%. Anything above that causes only rev increase but speed on gps does not change. That's why on previous recordings you noticed quickly going up and down. As soon I heard ventilation I took it down. View attachment 419157

I was mainly pointing out that you aren't allowing the engine to run at WOT at a steady state long enough to get valid results. Optimal trim of only 5% makes me question how the boat is loaded and/or prop selection.

 

[muc]

In post #149 you mentioned that maybe I have overloaded engine - wrong prop, gear ratio, engine misalignment. Is it anything else I can check with drive?

Also warn out or damaged engine was mentioned. What should I look for?
I removed spark plugs, checked them and did compression test again and got 180psi on each cylinder, cold engine 4 pufs.
Also took out exhaust manifolds for inspection and to get access to inspect valve rockers and springs.
Is it any way I can check timing without removing timing chain cover?
IDK maybe with dial gauge checking valves vs cylinder movements?

It sounds like you have checked the drive all you can, suggest you clean the water passages, install new impeller and test run the engine to see if that clears up the low sea water pressure issue. At that point you can WOT the engine and see what happens.
Other things you can check, put a long straight edge on the hull bottom and check for hooks or rockers. Check for anything that might affect water flow to the prop --- transducers or thru hulls. Try a 19p BlackMax prop like Mercury recommends.

Yes there are ways to check the timing chain. VERY time consuming and will require you to get Mercury to give you some info that they try to keep secret, not sure if they would give that out to a consumer.
I honestly feel you are a long ways off from going that far. I know you have read on the internet that this might be a possibility. But on this style of timing chain setup, in my 50 plus years of being a mechanic. I have never seen or heard (from reliable sources) of this actually happening.

 

[damo79]

It sounds like you have checked the drive all you can, suggest you clean the water passages, install new impeller and test run the engine to see if that clears up the low sea water pressure issue. At that point you can WOT the engine and see what happens.
Other things you can check, put a long straight edge on the hull bottom and check for hooks or rockers. Check for anything that might affect water flow to the prop --- transducers or thru hulls. Try a 19p BlackMax prop like Mercury recommends.

Yes there are ways to check the timing chain. VERY time consuming and will require you to get Mercury to give you some info that they try to keep secret, not sure if they would give that out to a consumer.
I honestly feel you are a long ways off from going that far. I know you have read on the internet that this might be a possibility. But on this style of timing chain setup, in my 50 plus years of being a mechanic. I have never seen or heard (from reliable sources) of this actually happening.

Since I was checking the valve springs, I also verified the valve timing. For cylinders 1 and 4, the intake valve pushrod lift begins at 18° BTDC and ends at approximately 108° ATDC. I also checked refluctor wheel center where (part with no tooth) and is positioned 88deg BTDC - checked inside sensor hole Used printed timing tape and dial indicator. Each cam lobe lift is 6.5mm. I guess that's all correct?