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Racey

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You’re not helping your engine or power running 91° you’re actually wasting money as the 496 cannot burn that fuel off. So you’re getting worse economy as well spending $0.30-0.50 more per gallon.

Mercury does a ton of research and they know better than cousin Bill or the dude that lives next door to your best friend. It’s all on their website.

That's not how octane ratings work, yes you are spending more money, but you aren't going down on power by running a higher octane rating.

The goal is NOT to buy the fuel that gets you closest to detonation, detonation is not power.

If you are leaving a lot of fuel sitting in the boat between trips you are better running 91 in order to get ahead of age degrading.

Also in applications running closed loop knock control, running higher octane lowers you chances of knock keeping you out of timing retard mode.

Mercury's entire reasoning for rating at 87 octane is because there are many places that only provide 87 fuel on the water.
 

Good Stuff

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If it wasn’t retuned from factory programming and the motor was rebuilt to factory specs then it doesn’t make sense that it wouldn’t have the same fuel specs as factory. 🤔
 

ChrisV

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Stock Ecu or tuned? Was it ever on the dyno? Or go drive it for couple hrs break in kinda thing?
 

DaveH

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that isn't rich, its STUPIDLY over fueled.

TPS calibrated improperly or faulty
MAP sensor seeing ambient only or faulty
injectors leaking
excessive fuel pressure
dare i say the tune is way off

another interesting thing, last week at an engine dyno, we tested some fresh chevron 91. it was 30% ethanol.
 

DaveH

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when the engine was rebuilt was the cam the same as stock? if not, and someone put a larger cam in that pulls less vacuum at idle, without touching the tune, you would over fuel at idle.
 

ChrisV

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when the engine was rebuilt was the cam the same as stock? if not, and someone put a larger cam in that pulls less vacuum at idle, without touching the tune, you would over fuel at idle.
This. I bet anything it’s still original map. Boat needs to go on the dyno or live tune on the water.
 

rivermobster

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So many questions!!!

First off...

Very few engine builders are EFI tuners. Not saying it Never works that way, but sending it back to the builder is probably a waste of resources.

There is a tuner in Havasu that can probably fix this properly for you.

When I talked to him about my buddies 502 rebuild, he wanted us to put 10/20 hours in it and then bring it to him.

We put O2 bungs in his CMI's awhile back, so it would be ready to go.

You need a real tuner to get a handle on this.

 

ChrisV

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So many questions!!!

First off...

Very few engine builders are EFI tuners. Not saying it Never works that way, but sending it back to the builder is probably a waste of resources.

There is a tuner in Havasu that can probably fix this properly for you.

When I talked to him about my buddies 502 rebuild, he wanted us to put 10/20 hours in it and then bring it to him.

We put O2 bungs in his CMI's awhile back, so it would be ready to go.

You need a real tuner to get a handle on this.

Problem with that is when something happens. Tuner gets blamed.
 

Waterheater

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This is kinda left field. I had a buddy with a 500 EFI that was having that problem. They completely rebuild the top end, reflashed the computer, basically everything. Still had the problem when they fired it up. This went on for 2 years. It sucked cleaning that crap off after pulling it out. One day we were sitting in his garage looking at it. He looks up the exhaust with a flashlight and you could see where the oil was coming into the exhaust where the water entered. turns out there was a hair line crack in his oil cooler. replaced the oil cooler, no more problems.
 

JD D05

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Obviously won't solve the real problem but I have a very nice set of clamp on downpipes and don't have any use for them.
 

gqchris

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I cant see how the engine builder would be responsible for the PCM tuning of the Merc motor. Im sure it was just a bolt everything back on type situation and dress it.

At least thats how it was when my buddy did his on his 496. And when I had PCM issues on my Warlock,. Whipple handled that.

If its any condolences, my transom is a bitch to clean also, but I am a little fatter for safety reasons.
 

Rbcconst

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I will have to see if I can find the build sheet, it's in my previous build thread. We didn't add any HP or anything from what I know.
Stock 525 runs on 87 not 91. You may have an injector issue as well. If an injector was stuck say in the open position you would have a lot of soot dump out, it happened to me on a 496. You could have them flow tested. Spark plug would be another possibility.
 

Joe mama

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New build, hopefully not some washed down cylinders.
 

Jay Dub

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In our 255 with 496HO, I run ethanol free 91 from Parker oil. Almost no soot
 

Bigbore500r

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@OldSchoolBoats - few questions to have the builder answer that will help eliminate potential culprits, or may even point in the right directon where it is plausible re-tuning may be required, or if something isn't right mechanically.

1) is ANYTHING different than a stock 525? When rebuilt - did they use same heads, same camshaft, same pistons? Other than bore size, was anything changed from stock spec?
2) is the ECM running the factory Merc 525 calibration?
3) Are the fuel injectors original from the previous 525? If they had them rebuilt - did they get flow sheets to show they are within OEM spec? If they replaced them - did they use factory injectors / same part # and mfg, or did they use aftermarket?
4) Still running factory Merc / CMI headers or has exhaust been changed?
5) Confirm throttle body is stock, not ported or modified. Same for intake manifold.

Once you know the answers above, these are the mechanical things they should check .

  1. Confirm no air leaks anywhere in intake system. Leaking intake gasket, unseated / unsealed MAP sensor, etc.
  2. Check fuel pressure under load - within spec?
  3. Verify timing is within spec (with a timing light, not just ECM data)
  4. Are the readings from the MAP and TPS sensors reading within the proper range (this affects fueling, if one is bad our out of spec)
  5. The spark plugs will ultimately determine if the motor is running rich - not the transom soot. Transom soot often happens when a motor is super rich, but it can look just like that when there is a slight oil leak. My boat has looked like that a few times - once it ended up being caused by gear oil from a recent outdrive service not being cleaned out from under my shift cover, water was mixing with it and it was somebow blowing the oil tainted water back on the transom while underway. Another time it started getting sooty for a few trips, and i traced it back to a weeping hydraulic steering ram - we're talking a slight leak!
  6. RE: Reading spark plugs - A fresh set of NGK plugs and a few passes up and down the lake will show if the motor is rich, and also if there are particular cylinders having the issue, or if it is uniform. This will also confirm the motor is happy with the timing curve, you will see it by the position of the burn on the ground strap. Note - NGK plugs are best for this because the material they use make them the easiest plugs to read BY FAR, for troubleshooting issues or turning for fuel / timing. If there are individual cylinders that are rich - need to check the fuel injector for that cylinder, as well as intake gasket seal, and compression / leak down. If there is oil on the plugs - you now have another culprit to investigate.
  7. Overall - compression and leakdown test if there are plugs that individually show noticable rich and/or oil compared to the others. Cranking PSI shoulud be checked at a minimum to make sure the camshaft timing has not been advanced or retarded inadvertantly, this will show up as lower or higher PSI that the factory 525 EFI due to the change in intake valve closing point. This only works as a reference with a factory cam - if the camshaft has been swapped with something different, dynamic / cranking compression will be a different value.

Hope that helps.
 
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Ziggy

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Stock 525 runs on 87 not 91. You may have an injector issue as well. If an injector was stuck say in the open position you would have a lot of soot dump out, it happened to me on a 496. You could have them flow tested. Spark plug would be another possibility.
If just one injector was pissing instead of spraying, one side would be dirtier.
 

mash on it

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Racey

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Problem with that is when something happens. Tuner gets blamed.

Or engine builder, this is why i never touch anything non motec without logging. First i know the motec systems inside out frontwards and backwards, second i always set up extreme datalogging.

Had a customer with a prerunner buggy blow a motor, me and DaveH pulled the data logs and brought in the google earth overlays.

1) heres where you unloaded the car andwent to foxes in Parker on your way to mexico 🤣 you were there for 2 hours.

2) here's the sand wash you were in when you got the first oil temp alarm

3) this channel is someone pushing the alarm clear button on the keypad

4) here is the second oil temp alarm

5) here is the canyon you were in when you pushed the alarm button again

6) here is you now running WOT after 2 oil temp alarms without stopping

.....

Uhhhhh you fuckers 🤣🤣🤣🤣
 

ChrisV

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Or engine builder, this is why i never touch anything non motec without logging. First i know the motec systems inside out frontwards and backwards, second i always set up extreme datalogging.

Had a customer with a prerunner buggy blow a motor, me and DaveH pulled the data logs and brought in the google earth overlays.

1) heres where you unloaded the car andwent to foxes in Parker on your way to mexico 🤣 you were there for 2 hours.

2) here's the sand wash you were in when you got the first oil temp alarm

3) this channel is someone pushing the alarm clear button on the keypad

4) here is the second oil temp alarm

5) here is the canyon you were in when you pushed the alarm button again

6) here is you now running WOT after 2 oil temp alarms without stopping

.....

Uhhhhh you fuckers 🤣🤣🤣🤣
Motec is the best. Can’t wait to use it in my car. 🤘🏻

But yes, the good ole, “ I was just cruising “ story
 

OCMerrill

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Was circling back to this thread to question this....
Ring wash. Its a thing. I used to work for an engine builder back in the late 80's. Built many engines, we would install, and tune them also.

The higher the octane then slower the flame front across the piston. Lower compression engines can leave unburnt fuel behind. Incomplete combustion especially with increased RPM. I Joe in danger of this? I would say if the problem persists he could be but he knows its not right and is communicating with the builder.
 
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OldSchoolBoats

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Did you ever find out why it blew the head gaskets in the first place before it was rebuilt? Motor is fresh but you may still have whatever caused that still going on.

They said detonation from bad gas. I am in touch with builder and they are committed to getting it sorted out. Have passed on a lot of the information from this thread.
 

hallett21

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Or engine builder, this is why i never touch anything non motec without logging. First i know the motec systems inside out frontwards and backwards, second i always set up extreme datalogging.

Had a customer with a prerunner buggy blow a motor, me and DaveH pulled the data logs and brought in the google earth overlays.

1) heres where you unloaded the car andwent to foxes in Parker on your way to mexico 🤣 you were there for 2 hours.

2) here's the sand wash you were in when you got the first oil temp alarm

3) this channel is someone pushing the alarm clear button on the keypad

4) here is the second oil temp alarm

5) here is the canyon you were in when you pushed the alarm button again

6) here is you now running WOT after 2 oil temp alarms without stopping

.....

Uhhhhh you fuckers 🤣🤣🤣🤣
lol I’ve never understood that. I’ve always told whoever is working on the motor exactly what happened. “Yes I was running it on the redline, yes something broke”.
 

rivermobster

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lol I’ve never understood that. I’ve always told whoever is working on the motor exactly what happened. “Yes I was running it on the redline, yes something broke”.

Ha...

I can't even count the crazy stories I heard, working at car dealerships, of why this should be warrantied!

Customers will lie like a rug.
 

NOTSOFAST

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Have you noticed any kind of oil slick around the back of boat at the dock or on the beach?
 

rivermobster

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I had a incredible story recently on a highly modded NSX, just driving down the freeway and parts came out of the motor.....

When I was a tech at Lexus...

"Custom states vibration while driving" Warranty ticket. No estimate given.

I rack the car and there are new parts stickers all over the place. Car had Obviously been in an accident.

Customer comes to inspect and says...

"I have been out of the country for a few months, and my business partner is the only one who had access to this car"

Apparently the business partner crashed it, had it repaired, and never said a word to the owner.

People are SO fucking shady.
 

Bigbore500r

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When I was a tech at Lexus...

"Custom states vibration while driving" Warranty ticket. No estimate given.

I rack the car and there are new parts stickers all over the place. Car had Obviously been in an accident.

Customer comes to inspect and says...

"I have been out of the country for a few months, and my business partner is the only one who had access to this car"

Apparently the business partner crashed it, had it repaired, and never said a word to the owner.

People are SO fucking shady.
Customer states - "The vibration is so bad it sonic cleaned the suspension parts on the way over here - those are original!"
 

rivermobster

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Customer states - "The vibration is so bad it sonic cleaned the suspension parts on the way over here - those are original!"

I gots shit tons of thieving customer stories.

People think dealerships are thieves? Some actually are. But I'll tell you right now, the customers are Far worse.

There are certain groups of people that have used the lemon laws to make money on a vehicle leases, AFTER driving the entire length of the (3 year) lease for free.

I gots stories for days...
 

mattyc

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Brand new rebuilt motor, got about 17 hours on it now.

Motor builder says run 91, so I run 91 from Campbell's or Shell along with adding Stabil Marine 360 at every fuel up.

Cleaning this every single morning is getting super annoying.

Any suggestions??

Would some turn down mufflers help?? The exhaust is straight pipe.


View attachment 1357098 View attachment 1357099
Has this been a problem since your first use of the boat after rebuild? Or has this condition become worse with use?
 

OldSchoolBoats

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Don’t do that. It then becomes someone guess. On the water tune with O2 sensors plugged into the tuner’s computer is the only way.. Brian Macy, horsepower connection in havasu.
Already got a couple texts recommending him.
 
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