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

[damo79]

MercNet, Dealer

Ha Ha, No longer a tech. Parts counter 18 hrs a week as my retirement hobby.
While I do have access to some confidential information, I only post things that I will freely give to customers that walk through the door.
Just please understand that we don’t help DIYer’s when we are busy with paying customers. That’s what this forum is for.

Do you know what was wrong with it back then? Was it repaired before auction or sold as it was?

 

[damo79]

@muc please see attached the recording of my previous checks. Idle, then steady plane at 3000, 4000 and WOT

 

[muc]

Only what found is vacuum pressure its 12in at idle and 0.5 at WOT. At 3000 7in and at 4000 3in. Correct at idle is 17-21. All sources on internet for 12in steady indicate problem with valves or timing chain. After season will take cover of and verify that.

The 12 inHg number you are worried about is from before the engine warm up state has completed. Unless you are troubleshooting a cold engine problem (you are not in this case) disregard all this info.

Once engine has completed warm up, you have about 17.6 inHg manifold pressure @ idle. Very normal number.

I'm guessing you might be getting confused about the manifold pressure numbers you see in Diacom. I'm not sure I can explain this properly (I'm not a very good teacher) but I will try.
If you hook up a mechanical vacuum gauge to a T that you install in the vacuum reference line to the fuel pressure regulator. Now KOEO and look at the gauge -- it will read zero, now look at Diacom -- it will read BARO and Manifold Pressure (MAP) as the same number, because the engine isn't running and there isn't any vacuum in the intake manifold. Now start the engine (KOER) and you will see BARO stay the same but MAP will read a lower number, now look at the gauge -- it will read the amount of vacuum in the manifold. If you want to check the accuracy of the gauge, take BARO and subtract MAP and you should get the gauge reading.
i.e. BARO 30 minus MAP 12 equals 18 inHg. Pretty high vacuum.
Does that make sense?
So a MAP reading of 0.5 @ WOT means there is almost no vacuum in the manifold.

So I think your barking up the wrong tree worrying about MAP numbers.

When you checked gear ratio did you disassemble and count teeth or count input shaft revolutions compared to prop shaft revolutions? In a situation like you have, I wouldn't trust the sticker on the side of the drive!

Also suggest you recheck fuel pressure how the manual recommends and report the all numbers to us.

 

[muc]

Do you know what was wrong with it back then? Was it repaired before auction or sold as it was?

I took a second look and I'm not sure this was a warranty return. It was registered by the warranty department.
It was auctioned with a one year warranty, so Merc felt it would last at least one year.
So my guesses are, warranty return and repaired, engine used at a tech school or maybe a engine used for display at boat shows?
Thinking about it, probably not a warranty return because if Merc called it back from a dealer, it was probably a problem a dealer couldn't fix. Making it unlikely Merc could fix it for resale.

 

[muc]

@muc please see attached the recording of my previous checks. Idle, then steady plane at 3000, 4000 and WOT

I looked at it but there is only about 6 minutes of data after engine reached completed warm up state and during that time and you were changing RPMs to much to allow the engine to stabilize. So not any real usable data. It never reached full PID!

When making a recording for diagnosis.
Run around until engine reaches complete warm up.
Now back to idle and then increase RPMs in 500 RPM increments holding steady at each for 5 minutes.
Really need to reach full PID to get numbers that are usable.

I did note that your trim usage was very unusual. I saw very little trim usage and did see it go into trailer mode? Maybe you have a problem with the trim sender?

During recording use the trim normally.

I hate to comment too much on this recording --- because garbage in garbage out --- but you had some misfire numbers I've never seen before.
And water pressure looks a little low.
I'll be very interested to see a good recording and see if they are still there. Maybe post a pic of your prop.

What I did see looked OK
injector on times, spark advance, fuel trim, fuel flow and MAP.
What's missing is O2 numbers.
But like I said garbage in garbage out.

 

[damo79]

I looked at it but there is only about 6 minutes of data after engine reached completed warm up state and during that time and you were changing RPMs to much to allow the engine to stabilize. So not any real usable data. It never reached full PID!

When making a recording for diagnosis.
Run around until engine reaches complete warm up.
Now back to idle and then increase RPMs in 500 RPM increments holding steady at each for 5 minutes.
Really need to reach full PID to get numbers that are usable.

I did note that your trim usage was very unusual. I saw very little trim usage and did see it go into trailer mode? Maybe you have a problem with the trim sender?

During recording use the trim normally.

I hate to comment too much on this recording --- because garbage in garbage out --- but you had some misfire numbers I've never seen before.
And water pressure looks a little low.
I'll be very interested to see a good recording and see if they are still there. Maybe post a pic of your prop.

What I did see looked OK
injector on times, spark advance, fuel trim, fuel flow and MAP.
What's missing is O2 numbers.
But like I said garbage in garbage out.

I will do it again tomorrow then and get some decent data.
When I did the recording you just reviewed noticed that engine was warmed up, got on plane waited for O2 status to change to closed loop and I was sure that it was the whole PID ongoing. What else to look for to be sure that its in full PID.

What do you mean by missing O2 numbers?

I agree that water pressure it should be higher. Not sure how it was before but few days ago got alarm 3-4 times with low pressure when started getting on plane. Checked it then in vessel view and it was like going up to 0.4-0.5bar up to 2000rpm and then when got on plane came below 0.05bar and that triggered alarm. Like mentioned 3-4 times and its fine since but low reading. Just before that I was refuelling in marina and saw lots of garbage in the water. My first thought was that probably plastic bag got suck in.
What do you think about this vaccum pressure at idle. 12-13"Hg its not normal. Checked manifold for leaks but found nothing.

 

[Fun Times]

What model stern drive is on the boat?
Is there a serial number on the drive itself and transom assembly too by chance?

 

[damo79]

Found screen shot from month ago and water pressure was much higher. It all changed that one day. Engine keeps right temperature maybe just pressure sensor is restricted. I would expect overheating if watter pressure is 1/5 of what it was few weeks ago.

 

[damo79]

What model stern drive is on the boat?
Is there a serial number on the drive itself and transom assembly too by chance?

It's alpha one gen 2.
1.62 ratio if I rememeber right

 

[damo79]

The 12 inHg number you are worried about is from before the engine warm up state has completed. Unless you are troubleshooting a cold engine problem (you are not in this case) disregard all this info.

Once engine has completed warm up, you have about 17.6 inHg manifold pressure @ idle. Very normal number.

I'm guessing you might be getting confused about the manifold pressure numbers you see in Diacom. I'm not sure I can explain this properly (I'm not a very good teacher) but I will try.
If you hook up a mechanical vacuum gauge to a T that you install in the vacuum reference line to the fuel pressure regulator. Now KOEO and look at the gauge -- it will read zero, now look at Diacom -- it will read BARO and Manifold Pressure (MAP) as the same number, because the engine isn't running and there isn't any vacuum in the intake manifold. Now start the engine (KOER) and you will see BARO stay the same but MAP will read a lower number, now look at the gauge -- it will read the amount of vacuum in the manifold. If you want to check the accuracy of the gauge, take BARO and subtract MAP and you should get the gauge reading.
i.e. BARO 30 minus MAP 12 equals 18 inHg. Pretty high vacuum.
Does that make sense?
So a MAP reading of 0.5 @ WOT means there is almost no vacuum in the manifold.

So I think your barking up the wrong tree worrying about MAP numbers.

When you checked gear ratio did you disassemble and count teeth or count input shaft revolutions compared to prop shaft revolutions? In a situation like you have, I wouldn't trust the sticker on the side of the drive!

Also suggest you recheck fuel pressure how the manual recommends and report the all numbers to us.

I know what diacom shows in regards to MAP explained it to someone just like you did few days ago under post #18.
During Diacom test vacuum gauge was connected to manifold and never showed more than 12.5" on idle. BTW see attached. It's below 13"

 

[Fun Times]

It's alpha one gen 2.
1.62 ratio if I rememeber right

Yes, it seems time to open up the drive to replace the impeller and inspect other water flow components ...Post the serial when you get a chance.

It's no catalyst version.

Here should be your engine parts list, https://www.mercruiserparts.com/4-5l-mpi-250-alpha-bravo-2a441953-thru-2a530777

Genuine Mercury Marine parts, large inventory, fast shipping

Genuine Mercury Marine, Mercruiser and Mercury Racing engines, parts, propellers. Authorized dealer with large inventory, great prices, fast shipping!

www.mercruiserparts.com

But, if possible, also post an overall photo of your engine as the catalyst statement seems sort of confusing.

Also post number 50 appears to be in need of editing as it's just a quote of Muc...

 

[damo79]

Yes, it seems time to open up the drive to replace the impeller and inspect other water flow components ...Post the serial when you get a chance.

Here should be your engine parts list, https://www.mercruiserparts.com/4-5l-mpi-250-alpha-bravo-2a441953-thru-2a530777

Genuine Mercury Marine parts, large inventory, fast shipping

Genuine Mercury Marine, Mercruiser and Mercury Racing engines, parts, propellers. Authorized dealer with large inventory, great prices, fast shipping!

www.mercruiserparts.com

But, if possible, also post an overall photo of your engine as the catalyst statement seems sort of confusing.

Also post number 50 appears to be in need of editing as it's just a quote of Muc...

I will take engine photo tomorrow. It's version with only one O2 sensor per exhaust. I was getting confused with that mercruiser site with parts too. Its not very clear there with serial numbers etc. That sticker tells you all about catalyst - not for sale in California.

 

[damo79]

@muc when it comes to drive im pretty sure with correct ratio. I checked online Bayliner VR5 performance done by boating magazines and at 3000rpm and 4000rpm a get exactly the same speed as they did during boat test. If prop or gear ratio was different than what they had in test boat speed won't be the same at same rpm.

 

[damo79]

Props - turning point 14.25x21 and I thought that boat was sluggish because of that and replaced with SS 14.5x19.
As long i won't see correct vacuum pressure I will be barking under that tree

 

[damo79]

@muc Checked manual and 45psi is correct fuel pressure for that engine.