496HO Engine performance issue.... opinions needed

[HubbaHubbaLife]

Sorry I’m late to the party. I have a 2005 Rage with the 496 HO. Agree with all the advice on the plugs. Mine has 300 hours and I’ve done them twice. Has anyone addressed the paint flaking off the cool fuel system? My mechanic spotted it last year..... when they first came up with the cool fuel system they painted the fuel regulators and the paint chipped off and got into the injectors. It could cause serious issues. With the help of Nordic Mercury Marine warrantied the issue my 13 year old boat. Best of luck resolving the issue.


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Thx XX14... that issue was revealed earlier. Appreciated.

 

[QC22]

he has seen numerous 496bplugs were you can spin the insulation piece , just spins around the center wire and it should not.

This is precisely what happened to mine. Year later had a plug wire get loose and exact same symptoms. FWIW, the insulation deal was intermittent. Sometimes the insulation movement allowed a spark, and sometimes prevented a spark.

 

[THE WIDGE]

This is precisely what happened to mine. Year later had a plug wire get loose and exact same symptoms. FWIW, the insulation deal was intermittent. Sometimes the insulation movement allowed a spark, and sometimes prevented a spark.

yeah, my mechanic showed me a box of various plugs w that issue , only in the 496, not the plug, but something w the harmonics of the motor that causes that piece to break

 

[adam909]

Just make sure you bleed all the air out of the system With the Schrader valve pretty simple

where is the valve located? and how is this done? cranck motor and release the air? pic of valve? thanks.

 

[HubbaHubbaLife]

Update.... mechanic did a compression test, all ok there. He's replacing ignition wires and spark plugs... he also noticed some moisture so will be replacing exhaust gaskets. He feels fairly confident this is the issue. If that doesn't cure it he'll be checking fuel injection system he says. Sound about right fellas?

 

[HubbaHubbaLife]

Updates.... Took boat out Sat/ Sun and all worked fine thank goodness. Whew.... and what a bargain, $800 ha. Should gone to mechanical school.

 

[Mcob25rg]

I've had 4 496HO's. I think your mechanic is spot on. Some owners will take out the turbulators ( restriction in exhaust elbow ) for better flow. When removed, water can seep down back into the heads and cause problems also, but the wires/plugs thing is a cronic problem with these.

 

[HubbaHubbaLife]

I've had 4 496HO's. I think your mechanic is spot on. Some owners will take out the turbulators ( restriction in exhaust elbow ) for better flow. When removed, water can seep down back into the heads and cause problems also, but the wires/plugs thing is a cronic problem with these.

Appreciate your comment.

 

[robby dmax]

where is the valve located? and how is this done? cranck motor and release the air? pic of valve? thanks.

if I remember correctly it is under the cover on the left side of the motor.. what I used to do was turn the key on and off a couple times(no start) let the fuel pump build a little pressure then with a rag around the valve just push in a little bit fuel a air is going to come out so be ready and keep covered.
Or you can buy a fuel pressure gauge with a bleeder on it and do it that way.
Hope that helps

 

[Lavey 29]

To add the exhaust turbulators are not only used on the mercruiser 496 but many other mercruiser engines. There is 2 main reason why they are installed. One is to burn off condensation the runs down the walls of the riser while the exhaust is heating and cooling. the turbulator acts as damn plus when warmed up is hot to boil away that condensation.

Also the main reason why the turbulators are installed for the 496 and other mercruiser engines is, it helps with water reversion - the smaller opening of the turbulator, this funnels and speeds up air velocity of the exhaust flow at idle speeds to help prevent water reversion.

 

[Lavey 29]

the OEM spark plugs wires on the 496 are actually 6.5 mm in diameter. They are week and gas fumes kills the boots and the outer portion of outer wire over time. All of Merc wires are made in Mexico FWIW

 

[Runs2rch]

the OEM spark plugs wires on the 496 are actually 6.5 mm in diameter. They are week and gas fumes kills the boots and the outer portion of outer wire over time. All of Merc wires are made in Mexico FWIW

Good to see you posting on here John! Throwing my wires in today.

 

[HubbaHubbaLife]

Sounds like somebody knows what they're talking about.....

 

[Lavey 29]

I’ll see if I can explain this accurately. My understanding is that upon throttle up, the ECU advances the timing temporarily to purposely induce a knock as a test of the knock sensor. If the sensor reads, then the ECU is good and restores timing to where it is supposed to be according to the conditions. If the sensor does not read, then the ECU throws a code and retards the timing in order to protect against any damage. This equals a loss of power.

If you are running 91, it is possible that the knock sensor would not activate during the temporary advance in timing and the ECU would respond accordingly.

In any case, the 496HO is designed to operate on 87. The black soot experienced by many is basically unburnt fuel. If you aren’t burning all the fuel you throw in the hole, that means a loss of power.

I’m not saying that’s definitely the case here, especially since the OP later indicated he normally runs 87, but it can be a problem when running higher octanes.

this is not happening with any 496 in the marine world. nor any other marine MPI OEM engines. Timing is effected by load and rpms based on the tables / calibrated / mapping within the ecm inwhich the marine oem set up for a jist of info. The ecm / pcm has no idea what octane the fuel has in the gas tank nor does the ecm have any idea what fuel pressure is while engine running for the Marine OEM side of things.

Just as the ecm / pcm does not know the octane of fuel that sat around for years meaning low octane stale fuel. The knock sensor job is to detect internal engine knock and retard timing.

Will add combustion of the fuel quality is a different story and does play a role of engine running condition but combustion of fuel has alot to with fuel delivery and the ignition for a jist. And really to get even talking further about fuel --- RVP really plays a huge role how well or not fuel is lite off per weather climate conditions --- meaning winter / spring / summer / fall blended fuels. I can not tell you how many times per year I see RVP of the fuel blend plays into poor engine running conditions. Back in the day we all talked about this at every Merc school and actually Merc wanted all their dealers service shops to have a RVP tester. Anyways for those who do not know what RVP is = reid vapor pressure.

Basically what you posted is ( MBT) = MEAN BEST TIMING for Thunderbolt V Carb engines using the Mercruiser Thunder bolt V ignition system. Merc Thunderbolt IV did NOT have this

 

[HubbaHubbaLife]

this is not happening with any 496 in the marine world. nor any other marine MPI OEM engines. Timing is effected by load and rpms based on the tables / calibrated / mapping within the ecm inwhich the marine oem set up for a jist of info. The ecm / pcm has no idea what octane the fuel has in the gas tank nor does the ecm have any idea what fuel pressure is while engine running for the Marine OEM side of things.

Just as the ecm / pcm does not know the octane of fuel that sat around for years meaning low octane stale fuel. The knock sensor job is to detect internal engine knock and retard timing.

Will add combustion of the fuel quality is a different story and does play a role of engine running condition but combustion of fuel has alot to with fuel delivery and the ignition for a jist. And really to get even talking further about fuel --- RVP really plays a huge role how well or not fuel is lite off per weather climate conditions --- meaning winter / spring / summer / fall blended fuels. I can not tell you how many times per year I see RVP of the fuel blend plays into poor engine running conditions. Back in the day we all talked about this at every Merc school and actually Merc wanted all their dealers service shops to have a RVP tester. Anyways for those who do not know what RVP is = reid vapor pressure.

Basically what you posted is ( MBT) = MEAN BEST TIMING for Thunderbolt V Carb engines using the Mercruiser Thunder bolt V ignition system. Merc Thunderbolt IV did NOT have this

Yaknow what I enjoy about this forum when it comes to tech? The second somebody shows up that knows his shit, the rest of us pipe down.

 

[Lavey 29]

^^^^^ OEM Stock Mercruiser for the 8.1 L - 496 CID specs for oil pressure ( fully warmed engine) using their 25 W 40 Motor oil -- min. at dead idle rpms is 15 psi and min. oil pressure at 2000 rpms is 30 psi. This is per their service manual and training class.

I would check your gauge reading vs a scan readings vs a mechanical gauge reading. Also possible wrong weight oil, Also possible bad oil pressure sender for off oil pressure readings..

 

[HubbaHubbaLife]

^^^^^ OEM Stock Mercruiser for the 8.1 L - 496 CID specs for oil pressure ( fully warmed engine) using their 25 W 40 Motor oil -- min. at dead idle rpms is 15 psi and min. oil pressure at 2000 rpms is 30 psi. This is per their service manual and training class.

I would check your gauge reading vs a scan readings vs a mechanical gauge reading. Also possible wrong weight oil, Also possible bad oil pressure sender for off oil pressure readings..

Thanks much... will do.

 

[HubbaHubbaLife]

Thanks much... will do.

^^^^^ OEM Stock Mercruiser for the 8.1 L - 496 CID specs for oil pressure ( fully warmed engine) using their 25 W 40 Motor oil -- min. at dead idle rpms is 15 psi and min. oil pressure at 2000 rpms is 30 psi. This is per their service manual and training class.

I would check your gauge reading vs a scan readings vs a mechanical gauge reading. Also possible wrong weight oil, Also possible bad oil pressure sender for off oil pressure readings..

Lavey 29.... If you don't mind I want to get your opinions again. I'm still having some lack of power in the 3-4K rpm range. Some back firing and just a lack of full thrust if ya get my drift. My mechanic [who is new to me] diagnosed compression to be fine and changed the spark plugs/ wires as stated in this thread earlier. He said lets see if this fixes issue.... he indicated it may be a fuel injection issue if persist. Well, its persisting.... what are your thoughts please. Thank you. PS 496HO with 550 hours.... lower rpm usage as I only boat through Newport Harbor [no wake] and only run near shore north & south in Orange County hitting maybe 40 MPH max due to chop most days. Appreciate your thoughts!

 

[Shlbyntro]

Lavey 29.... If you don't mind I want to get your opinions again. I'm still having some lack of power in the 3-4K rpm range. Some back firing and just a lack of full thrust if ya get my drift. My mechanic [who is new to me] diagnosed compression to be fine and changed the spark plugs/ wires as stated in this thread earlier. He said lets see if this fixes issue.... he indicated it may be a fuel injection issue if persist. Well, its persisting.... what are your thoughts please. Thank you. PS 496HO with 550 hours.... lower rpm usage as I only boat through Newport Harbor [no wake] and only run near shore north & south in Orange County hitting maybe 40 MPH max due to chop most days. Appreciate your thoughts!

I would like to see the compression numbers if he has them. As simple good/not good compression test result is completely worthless in my eyes, I also want to know how the spark plugs looked when they came out of the engine, has it been burning evenly, are some cylinders rich and some lean? However It is extremely likely that you are having a fuel issue if the compression actually is good. A fuel pressure test at idle can verify this. Any more than 43 PSI or substantial fluttering would indicate a problem. If you have the gen3 cool fuel module as most 496s do, they were known to shed paint into the fuel system which in turn would clog the fuel pressure regulator and creat havoc with the injectors, sometimes clogging them and creating lean cylinders and other times causing them to stick open and causing rich/flooded cylinders. THIS IS THE NUMBER ONE CAUSE OF CATOSTROPHIC ENGINE FAILURE IN A 496. Please have your mechanic verify that your engine is a candidate for Mercurys free fuel system parts replacement program. They will provide parts, and you will be responsible for your mechanics labor.

 

[HubbaHubbaLife]

I would like to see the compression numbers if he has them. As simple good/not good compression test result is completely worthless in my eyes, I also want to know how the spark plugs looked when they came out of the engine, has it been burning evenly, are some cylinders rich and some lean? However It is extremely likely that you are having a fuel issue if the compression actually is good. A fuel pressure test at idle can verify this. Any more than 43 PSI or substantial fluttering would indicate a problem. If you have the gen3 cool fuel module as most 496s do, they were known to shed paint into the fuel system which in turn would clog the fuel pressure regulator and creat havoc with the injectors, sometimes clogging them and creating lean cylinders and other times causing them to stick open and causing rich/flooded cylinders. THIS IS THE NUMBER ONE CAUSE OF CATOSTROPHIC ENGINE FAILURE IN A 496. Please have your mechanic verify that your engine is a candidate for Mercurys free fuel system parts replacement program. They will provide parts, and you will be responsible for your mechanics labor.

Interesting thanks. Will do.

 

[Outdrive1]

Anytime a 496 has running issues, change the plugs.

 

[HubbaHubbaLife]

Anytime a 496 has running issues, change the plugs.

Thanks.... this is kinda a lengthy thread from my original issues..... the mechanic changed plugs as well as put on new wires. So that wasn't it apparently so now I have to get him [or someone else] to look deeper into cause...... always appreciate ideas & experiences of course. This 496HO is a super common engine I've learned so trouble shooting shouldn't be too tough I'd think.

 

[Outdrive1]

Thanks.... this is kinda a lengthy thread from my original issues..... the mechanic changed plugs as well as put on new wires. So that wasn't it apparently so now I have to get him [or someone else] to look deeper into cause...... always appreciate ideas & experiences of course. This 496HO is a super common engine I've learned so trouble shooting shouldn't be too tough I'd think.

Sorry I didn’t read the whole thread but those plugs are pretty common. I’ve seen the fuel regulator go out and cause running issues as well but it’s not super common. Those motors are pretty bullet proof in stock form.


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[HubbaHubbaLife]

Sorry I didn’t read the whole thread but those plugs are pretty common. I’ve seen the fuel regulator go out and cause running issues as well but it’s not super common. Those motors are pretty bullet proof in stock form.


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Thanks.... always hoping for an easy fix. thats why I got the 496.... I heard the 500 & 525s are a bit more temperamental.

 

[LGETT]

Maybe I missed it when thumbing through your post but a leak down test will be much more complete to insure full seal. Checks valve seal, ring seal, headgasket, cracked cylinder or head, etc.

Second a member friend here had a 496 with an injector issue and had similarsymptoms. sending them out after 500hrs of ethanol fuel for cleaning and flow bench is not very expensive. Think last 8 I sent out was around $300

Good luck

 

[HubbaHubbaLife]

Maybe I missed it when thumbing through your post but a leak down test will be much more complete to insure full seal. Checks valve seal, ring seal, headgasket, cracked cylinder or head, etc.

Second a member friend here had a 496 with an injector issue and had similarsymptoms. sending them out after 500hrs of ethanol fuel for cleaning and flow bench is not very expensive. Think last 8 I sent out was around $300

Good luck

Thanks man.... taking all this down.

 

[Lavey 29]

the mercruiser gen 3 cool fuel is in many mercruiser apps not just the 496. -- the gen 3 cool fuel was installed on all 2006 model year and up. 2005 and back the Merc did not even have a GEN 3 cool fuel.

For many who do not know --- all marine OEM stock engines go by engine serial numbers per how they are set up -- per how a tech services and repair procedure -- per what service manuals are used and related parts per that engine serial number to buy and install.

All Boaters need to know their engine serial number. So why would I stress this so much. Lets use the 496 Mercruiser for an example. a 2001 496 is not the same as 2002 / 2003 model year nor is a 2004 model year the same nor is a 2006 model year the same nor is the 2008 California CARB EMISSION CONTROLED 496 engine the same -- barely anything is the same here for that engine. Then we have the 2010 496 totally different again not the same as any past 496 s. The 496 has many changes per engine serial number runs thru out its life 2001 - 2010 marine world. Just saying

If you have a GEN 3 cool fuel -- you will have issues 1000 percent with paint peeling in the upper portion of the cool fuel gen 3 - it will be all around the fuel pressure regulator and all in the injectors. ( the black shedding paint ). This issue has taken place from model years 2006 thru 2018 for all gen 3 cool fuels. Back in 2007 and unheard of --- but finding this issue out because I serviced fuel injectors for 15 years now. Anyways in 2007 on a Merc 496 - spring commission - poor running engine for a jist - I pulled the fuel injectors out to examine. I found black paint in the fuel injectors. To my surprise I called around to other techs and including you know who to ask how in the hell is large black paint flakes getting in the fuel injectors. Short story was in spring 2007 --- basically deer in the headlites was the answers I was getting at that timeframe. Low and behold as we all know --- all gen 3 cool fuels sheds paint like no tomorrow.

 

[Lavey 29]

if a 496 idles real well and accels good its not the spark plugs

 

[Shlbyntro]

the mercruiser gen 3 cool fuel is in many mercruiser apps not just the 496. -- the gen 3 cool fuel was installed on all 2006 model year and up. 2005 and back the Merc did not even have a GEN 3 cool fuel.

For many who do not know --- all marine OEM stock engines go by engine serial numbers per how they are set up -- per how a tech services and repair procedure -- per what service manuals are used and related parts per that engine serial number to buy and install.

All Boaters need to know their engine serial number. So why would I stress this so much. Lets use the 496 Mercruiser for an example. a 2001 496 is not the same as 2002 / 2003 model year nor is a 2004 model year the same nor is a 2006 model year the same nor is the 2008 California CARB EMISSION CONTROLED 496 engine the same -- barely anything is the same here for that engine. Then we have the 2010 496 totally different again not the same as any past 496 s. The 496 has many changes per engine serial number runs thru out its life 2001 - 2010 marine world. Just saying

If you have a GEN 3 cool fuel -- you will have issues 1000 percent with paint peeling in the upper portion of the cool fuel gen 3 - it will be all around the fuel pressure regulator and all in the injectors. ( the black shedding paint ). This issue has taken place from model years 2006 thru 2018 for all gen 3 cool fuels. Back in 2007 and unheard of --- but finding this issue out because I serviced fuel injectors for 15 years now. Anyways in 2007 on a Merc 496 - spring commission - poor running engine for a jist - I pulled the fuel injectors out to examine. I found black paint in the fuel injectors. To my surprise I called around to other techs and including you know who to ask how in the hell is large black paint flakes getting in the fuel injectors. Short story was in spring 2007 --- basically deer in the headlites was the answers I was getting at that timeframe. Low and behold as we all know --- all gen 3 cool fuels sheds paint like no tomorrow.

Yep, I've already done 6 fuel system "recalls" this year alone. Not just 496s. (But 496s tend to be the ones that blow up when this happens)

However, all gen3 cool fuels are susceptible to this up until the change ove to the anodized top caps. Including the 4.3L bravos.

If any of you out there have them and havent taken advantage of it yet, have your system overhauled while Mercruiser is still gifting you the parts.!

They record the serial numbers of every engine that has had it performed so even if you're not the original owner, a call to them with your serial number to ask if it's been performed on your boat yet or not is worth while, just be sure to let them know that you are experiencing running issues when you ask about it.

 

[Lavey 29]

The problem child paint peelers have to go back to the dealer for any of that to happen. A new anodized top gen 3 cool fuel - the fuel rail and the fuel injectors to get changed out for the gifting parts only.

 

[HubbaHubbaLife]

if a 496 idles real well and accels good its not the spark plugs

Ah, there you are. I copied your above post and sending to mechanic. As far as idle and out of the hole.... idle seems good not stalling as I work shift back n forth at docks. The hole shots aren't 100% strong, just feels like something is missing, and then at 3-4K rpm I hear missing and backfiring out exhaust. That's the b est way I can explain the symptoms. Thanks Lavey29.

 

[HubbaHubbaLife]

Yep, I've already done 6 fuel system "recalls" this year alone. Not just 496s. (But 496s tend to be the ones that blow up when this happens)

However, all gen3 cool fuels are susceptible to this up until the change ove to the anodized top caps. Including the 4.3L bravos.

If any of you out there have them and havent taken advantage of it yet, have your system overhauled while Mercruiser is still gifting you the parts.!

They record the serial numbers of every engine that has had it performed so even if you're not the original owner, a call to them with your serial number to ask if it's been performed on your boat yet or not is worth while, just be sure to let them know that you are experiencing running issues when you ask about it.

Thx much.... copied and sent to my tech.

 

[02HoWaRd26]

Update.... mechanic did a compression test, all ok there. He's replacing ignition wires and spark plugs... he also noticed some moisture so will be replacing exhaust gaskets. He feels fairly confident this is the issue. If that doesn't cure it he'll be checking fuel injection system he says. Sound about right fellas?

Can order wires in a spirocore from Taylor for 125$ vs the 350$ ones from Mercruiser as well. If replacing plugs use the TRIX55

 

[02HoWaRd26]

Yep, I've already done 6 fuel system "recalls" this year alone. Not just 496s. (But 496s tend to be the ones that blow up when this happens)

However, all gen3 cool fuels are susceptible to this up until the change ove to the anodized top caps. Including the 4.3L bravos.

If any of you out there have them and havent taken advantage of it yet, have your system overhauled while Mercruiser is still gifting you the parts.!

They record the serial numbers of every engine that has had it performed so even if you're not the original owner, a call to them with your serial number to ask if it's been performed on your boat yet or not is worth while, just be sure to let them know that you are experiencing running issues when you ask about it.

How exactly does a do it yourself guy do this or is it a merc dealer only job?

 

[HubbaHubbaLife]

Can order wires in a spirocore from Taylor for 125$ vs the 350$ ones from Mercruiser as well. If replacing plugs use the TRIX55

Thx... tech replaced plugs/ wires when first troubleshooting.

 

[Shlbyntro]

How exactly does a do it yourself guy do this or is it a merc dealer only job?

Mercury will only authorize if a Merc dealer submits a claim. You would need to have a good friend whose a Merc dealer submit a claim on your behalf and who trusts you to do the repairs yourself because their name will be attached to it

 

[HubbaHubbaLife]

the mercruiser gen 3 cool fuel is in many mercruiser apps not just the 496. -- the gen 3 cool fuel was installed on all 2006 model year and up. 2005 and back the Merc did not even have a GEN 3 cool fuel.

For many who do not know --- all marine OEM stock engines go by engine serial numbers per how they are set up -- per how a tech services and repair procedure -- per what service manuals are used and related parts per that engine serial number to buy and install.

All Boaters need to know their engine serial number. So why would I stress this so much. Lets use the 496 Mercruiser for an example. a 2001 496 is not the same as 2002 / 2003 model year nor is a 2004 model year the same nor is a 2006 model year the same nor is the 2008 California CARB EMISSION CONTROLED 496 engine the same -- barely anything is the same here for that engine. Then we have the 2010 496 totally different again not the same as any past 496 s. The 496 has many changes per engine serial number runs thru out its life 2001 - 2010 marine world. Just saying

If you have a GEN 3 cool fuel -- you will have issues 1000 percent with paint peeling in the upper portion of the cool fuel gen 3 - it will be all around the fuel pressure regulator and all in the injectors. ( the black shedding paint ). This issue has taken place from model years 2006 thru 2018 for all gen 3 cool fuels. Back in 2007 and unheard of --- but finding this issue out because I serviced fuel injectors for 15 years now. Anyways in 2007 on a Merc 496 - spring commission - poor running engine for a jist - I pulled the fuel injectors out to examine. I found black paint in the fuel injectors. To my surprise I called around to other techs and including you know who to ask how in the hell is large black paint flakes getting in the fuel injectors. Short story was in spring 2007 --- basically deer in the headlites was the answers I was getting at that timeframe. Low and behold as we all know --- all gen 3 cool fuels sheds paint like no tomorrow.

Lavey29.... finally spoke with a Mercruiser certified dealer who was recommended..... he totally knew about what you mentioned above, thanks....He'll be coming out to do diagnosis soon. Hoping for a oem warranty situation..... I'd never had known about this issue otherwise and it appears quality mechanics are rare.

 

[HubbaHubbaLife]

As mentioned before, try fresh spark plugs and changing both the disc and cartridge fuel filters. I recommend acdelco 41-983 plugs.

Pay careful attention to the spark plugs to see if there is any kind of uneven burning between different cylinders, I also always so a compression test with my tune ups for piece of mind.


That being said there is a service bulletin on your motor where paint likes to come loose from the inside of the fuel pump after the filters and gets sent down the line on the fuel system causing higher fuel pressure by clogging the fuel pressure regulator and sometimes causes erratic fuel injector behavior to where some injectors can be dumping fuel and others can not be giving enough fuel. All of which can cause the running issues you're describing

I finally got a mechanic scheduled to come to boat Monday and start diagnostics... I'll be pointing directly at the issue you've mentioned. Thanks!. I'll let you know how all this transpires.

 

[HubbaHubbaLife]

Mercury will only authorize if a Merc dealer submits a claim. You would need to have a good friend whose a Merc dealer submit a claim on your behalf and who trusts you to do the repairs yourself because their name will be attached to it

Just locating a mechanic has been quite a point of frustration... man I didn't know how lucky I've been all these years to have a top mechanic. He moved away so now I'm going with a guy off Yelp. All the mechanics around here are overwhelmed with business. I found a Merc authorized dealer and once they learned it was a warranty situation they ran from the work.

 

[HubbaHubbaLife]

the mercruiser gen 3 cool fuel is in many mercruiser apps not just the 496. -- the gen 3 cool fuel was installed on all 2006 model year and up. 2005 and back the Merc did not even have a GEN 3 cool fuel.

For many who do not know --- all marine OEM stock engines go by engine serial numbers per how they are set up -- per how a tech services and repair procedure -- per what service manuals are used and related parts per that engine serial number to buy and install.

All Boaters need to know their engine serial number. So why would I stress this so much. Lets use the 496 Mercruiser for an example. a 2001 496 is not the same as 2002 / 2003 model year nor is a 2004 model year the same nor is a 2006 model year the same nor is the 2008 California CARB EMISSION CONTROLED 496 engine the same -- barely anything is the same here for that engine. Then we have the 2010 496 totally different again not the same as any past 496 s. The 496 has many changes per engine serial number runs thru out its life 2001 - 2010 marine world. Just saying

If you have a GEN 3 cool fuel -- you will have issues 1000 percent with paint peeling in the upper portion of the cool fuel gen 3 - it will be all around the fuel pressure regulator and all in the injectors. ( the black shedding paint ). This issue has taken place from model years 2006 thru 2018 for all gen 3 cool fuels. Back in 2007 and unheard of --- but finding this issue out because I serviced fuel injectors for 15 years now. Anyways in 2007 on a Merc 496 - spring commission - poor running engine for a jist - I pulled the fuel injectors out to examine. I found black paint in the fuel injectors. To my surprise I called around to other techs and including you know who to ask how in the hell is large black paint flakes getting in the fuel injectors. Short story was in spring 2007 --- basically deer in the headlites was the answers I was getting at that timeframe. Low and behold as we all know --- all gen 3 cool fuels sheds paint like no tomorrow.

I've finally located a mechanic and am on his schedule tomorrow .... I'll be sharing all your feedback with him for sure, really appreciate your expertise and I'll circle back once he's identified and resolved the issue.

 

[HubbaHubbaLife]

As mentioned before, try fresh spark plugs and changing both the disc and cartridge fuel filters. I recommend acdelco 41-983 plugs.

Pay careful attention to the spark plugs to see if there is any kind of uneven burning between different cylinders, I also always so a compression test with my tune ups for piece of mind.


That being said there is a service bulletin on your motor where paint likes to come loose from the inside of the fuel pump after the filters and gets sent down the line on the fuel system causing higher fuel pressure by clogging the fuel pressure regulator and sometimes causes erratic fuel injector behavior to where some injectors can be dumping fuel and others can not be giving enough fuel. All of which can cause the running issues you're describing

Just circling back with ya for my update. Its taken all this time to get a mechanic to do mobile service in Newport. They all are overwhelmed with business at present. I had to find my guy on Yelp so hoping for best. He arrives tomorrow to do diagnostic work over laptop software. I've let him know about the paint flecking off and clogging injectors issue so he'll start looking there first. I can tell he's not as sharp as my past mechanic.... but its all I got at present. Let ya know how this finishes out. I also now have a service manager finally returning my calls.... spoke with him and he's very aware of that issue in Merc 496HOs. So he'll be my plan B. Thanks again!

 

[Lavey 29]

I have to say if you have a real boat mechanic and he does not nor DID NOT know about the paint shedding mercruiser gen 3 cool fuel modules - I would have to say you better find another boat mechanic. I knew about this issue since mid season 2007. Its extremely common issue and not only for the 496 but all mercruiser engines using it. The GEN 3 cool fuel is used on the 4.3 MPI and up with Bravo outdrive apps.

Personally Pulled out fuel injectors from that 496 in 2007 and hell the injectors were loaded with black paint. The engine ran very poor to say the least. When I started to call around and up to WI, it was deer in the head lites on the other end of the phone. Way back then,

The Mercruiser Gen 3 cool fuel came out past mid season 2005 for model year 2006.

All Merc gen 3 cool fuel modules shed paint past the filters regardless - no way around that period. The fuel damper gets loaded with black paint as well. MANY miss that area and replug the injectors all over again. You can lead those horses to water but you can not make them drink. My point clean the whole darn fuel system and get a brand new current gen 3 cool fuel and call it a day. You can get the injectors cleaned and flow tested or get new ones. Those injectors I bring back to new all the time. They actually are pretty tough injectors installed on the 496s injectors.

 

[HubbaHubbaLife]

Update.... finally got tech onboard today to take boat out while laptop hooked up for diagnosis under power. Indicates low oil pressure. Idles around 20 psi while should be something closer to 27..... while under load accelerating only saw 25psi while should be in 35-40 range. Tech believes it may simply need an oil/ filter change. [Its been around 100 hours] Hoping for best... gonna change and take out tomorrow. He also put fresh fuel in w/ Techron additive. Obviously hoping for the cheap fix .... otherwise he suspects a bad oil pump. Says that requires removal of motor to get at it. Also want him to look into the fuel system based on everything you guys mentioned in this thread. Thanks.

 

[Shlbyntro]

Update.... finally got tech onboard today to take boat out while laptop hooked up for diagnosis under power. Indicates low oil pressure. Idles around 20 psi while should be something closer to 27..... while under load accelerating only saw 25psi while should be in 35-40 range. Tech believes it may simply need an oil/ filter change. [Its been around 100 hours] Hoping for best... gonna change and take out tomorrow. He also put fresh fuel in w/ Techron additive. Obviously hoping for the cheap fix .... otherwise he suspects a bad oil pump. Says that requires removal of motor to get at it. Also want him to look into the fuel system based on everything you guys mentioned in this thread. Thanks.

That oil pressure is on the low side, but not so low to where its causing a running problem...

Compression test, fuel sample, and read the spark plugs before anything else. Then replace plugs if compression is good. If you dont have an engine alarm the oil pressure doesn't have anything to do with the running issue.

I'm sitting here bewildered at what this guy is telling you....

 

[HubbaHubbaLife]

That oil pressure is on the low side, but not so low to where its causing a running problem...

Compression test, fuel sample, and read the spark plugs before anything else. Then replace plugs if compression is good. If you dont have an engine alarm the oil pressure doesn't have anything to do with the running issue.

I'm sitting here bewildered at what this guy is telling you....

Man I was afraid you'd say what you did. I have minimal faith in this guys abilities thus far. I'm just kind of stuck with him at moment because techs are so booked up. Even he is booked 3 weeks out. I'll let him do his oil/ filter change tomorrow and we'll run it. If still have issue I'm telling him to check fuel system as you and Lavey29 have mentioned. I can tell this dude needs guidance. Thanks!

 

[Lavey 29]

grab a mechanical oil pressure gauge and verify the readings the mechanical gauge vs the dash gauge reading vs the scan tool reading

 

[Lavey 29]

her

^^^^^ OEM Stock Mercruiser for the 8.1 L - 496 CID specs for oil pressure ( fully warmed engine) using their 25 W 40 Motor oil -- min. at dead idle rpms is 15 psi and min. oil pressure at 2000 rpms is 30 psi. This is per their service manual and training class.

I would check your gauge reading vs a scan readings vs a mechanical gauge reading. Also possible wrong weight oil, Also possible bad oil pressure sender for off oil pressure readings..

HERE AGAIN

 

[HubbaHubbaLife]

her



HERE AGAIN

Yup he did that Thursday with his laptop diagnostic software as we cruised through rpms at sea. It showed lower than normal oil pressure so he changed oil/ filter Friday and I had a conversation regarding his ability to check fuel system next. I wanted to give him the opportunity to bow out with dignity. He acknowledged that he works primarily on diesel engines and I agreed to pay him for time/ materials and be on his way. I have our local yacht dealers service tech coming out this week to basically start from scratch and after a lengthy conversation Friday he agrees with what you have indicated and is very experienced with this generation 496HO so he'll get into this M-F and will report his findings. I'll report back and thanks again for your expertise.

 

[DrHW]

Did the Boat sit for a while before you took it out recently?

 

[HubbaHubbaLife]

Did the Boat sit for a while before you took it out recently?

No, I wish.... I go out maybe two/ three times a month....this thread has been a lengthy informative one for sure and I have zero mechanical expertise however I'm feeling better about finally locating a qualified tech in my area who has me on their schedule this week. That coupled with a couple dudes on here that I can tell have vast experience working on my particular engine. Fingers crossed.