496 HO Burning Pistons
 

Unfortunately I'm dealing with a recurring problem with one of two 496 HOs installed in my boat that I can't find a smoking gun. At 225 hours, cylinder #1 of the starboard motor burned the edge of the piston. Had the motor rebuild (builder said he tested the injectors), then I had a marine tech ride with me plugged in to the PCM with a Diacom unit to watch the engine vitals (reports attached). After finding nothing wrong, I chalked the problem up to bad gas (each motor has it's own tank).

Port Motor Report (still running awesome with 450 hours)
Starboard Motor Report (failed twice)

Fast forward another 225 hours and the same problem happens again (not sure which jug yet) to the starboard motor. I got a great deal on two new First Mate long blocks, so opted to just do both motors as the port motor was now at 450 hours anyway. I pulled all (16) injectors (which after removing them was easy to see the original rebuilder lied to me as the paint was still bonding the connector to the injector) and sent them to Mr Injector to be flow tested and rebuilt. His report showed only a 3% decrease in output from injector to injector :confused: so here i am again without the smoking gun.

What am I missing (besides a stack of Benjamins for buying a 496 to begin with)? I remember a few years back when Ray was active in the 496 topics, he stated the 3/8 ID fuel lines builders use on these motors is a source of problems, any one else have suggestions or experience with this?

maybe pick up tube sucking air a cracked.

Not a lot to go on as to why you're burning pistons ...what is odd is the negative timing data , I would somehow hook up a 02 sensor
and monitor air - fuel ratio at various throttle positions , also see if you can get a lap top and monitor injector pulse - width .

Internal fuel rail corrosion and leads to fuel injectors contamination that causes restrictions in which causes lean conditions. yoiur full injectors need to be flow tested and most likely new fuel rails or at least checked very closely.

I do fuel injector flow testing and cleaning. I am working on HO 496 that has this same exact problem with fuel rail corrosion and really bad injectors. If anyone can post pics for me I will be gladly to show what the fuel injectors look like internally.

I opened up your scan reports just now and took a quick look at them.. they were with 225 / 226 hours on them back in 2008. You do not have a current scan ?

back then the port engine had a about 6 faults or more. you have crank and cam sensor faults, low voltage, both exhaust manifold temps, Overspeed,, low block pressure, guardian mode for almost 1700 seconds in which is a lot.

Did you get all that fixed as you state the motor has 450 hours and runs good ? surely it could not have been running good back then when the scan took place.

A current scan of your both motors might pin point something better than a scan 7 years ago with half the hours on them.. Just saying.

Thanks for the suggestions thus far.

The scans posted followed my original failure, nothing since then as the new motors are not completely installed yet. I did pull the rails and have the injectors all cleaned, rebuilt and tested by Mr Injector, however the flow testing prior to beginning the work showed it was unlikely this was the source of failure as all injectors performed within 3% of rating. Also related to the fuel rail, internally there is no corrosion and looked smooth and clean.

the faults I was told are normal, as the waters we boat on eat sea water pumps...so its not uncommon to see faults logged related to water supply. The low block pressure I didn't notice before...what system does that relate to?

I am leaning (no phun intended), toward a problem on the suction side (too small of a supply hose or air leak in tank siphon) as Ray mentioned this in a previous post about the 496.

All this "stuff" can be had from CP Performance and eBay relatively cheap. Start at the tank and confirm everything is acceptable.

For what its worth, I replaced most of this stuff already. Upon rebuilds, I replaced the tank pickup with 1/2 inch (CP Performance), all new injectors (eBay), swapped out the fuel rails for new ones (eBay), last, i upgraded the fuel pump and piece of crap regulator to Aeromotive.

Have you analyzed your fuel water separator? Tear them down and see whats in them with an oil filter cut off tool. Maybe you have a tank issue with debris?

hey KA, I'm comfortable with the injectors and fuel rail now, but the fuel pump and regulator, along with the tank/supply lines are all unknown right now. I would think the smartcraft system would shut the motor down to guardian if supply pressure was too low? Can you provide me the details of your pump and regulator you upgraded to? Also, are you still using the inline filter between the tank and the water separator filter?

There is fuel tests that can be done both at the sametime to see if you have a suction side restriction or air and of course proper fuel pressure tests thru out the rpms.

You want to check fuel for restrictions or air leaks with a vacuum gauge and a clear fuel line hose coming out of the gas tank hooked right after your metal canister inline fuel filter, Tee in your vacuum gauge into that clear fuel line right after the inline fuel filter.

U are looking for a very solid fuel flow thru your clear fuel line and no more (MAX) of 2 hg inches of vacuum. anything under 2 hg inches the better and of course the solid fuel flow going thru your clear fuel line. You are looking for air bubbles, if present you have a problem either with a restriction and or air leak. plus looking for any vacuum reading that is over 2 hg inches, I really like 1 hg inches or under if all possible for fuel vacuum reading testing.

The next testing is with the fuel pressure gauge to make sure you have the proper spec on that side of it as well.

The clear fuel line is for testing purposes only. Just to be clear on my end.

Are these closed cooling systems?

Check the antifreeze and make sure its not full strength the motor will run hot and detonate. I have seen this many times before in cars and heavy equipment. Had a ford would drive it down the road and it would sound like marbles came back to the yard dropped a gallon out and put water in and problem was gone.

reported 431 deg f lake water temp.i think that sensor might be faulty!what is this BUP?

jeez Mike I was going to ask that same question. No actually its relates to the paddle wheel in which serves 2 purposes if you have one. In which in his case I would say 99 % he does not. The paddle wheel spins for MPH reading and has a sea water temp sensor built into it so it can read water temps as well. Without the paddle wheel connected / linked to smartcraft and in his case he does not have one - the temp reading will default to what the highest listing was. Temp 431.60. If you notice both engine scans read the same exact 431.60 (default number) for the basic jist of this.

There you go for todays lesson. LOL

good info as usual.

What is the fuel pressure at full load?

unfortunately I don't have that number right now hallj, this is probably going to take several weeks as I have to break in a couple motors before I'll be able to run WOT to verify pressure side. I love the idea of a vacuum gauge on the source side and the clear tube for visual verification (you can see the inline filters mounted to the bulkhead at the front of the engine well). Couple pictures below of the fun :food-smiley-007:

http://www.intored.net/media/496/Bilge.JPG

http://www.intored.net/media/496/Dressing.JPG

http://www.intored.net/media/496/Intake.JPG

http://www.intored.net/media/496/Crane.JPG

http://www.intored.net/media/496/Install.JPG

well you dove right onto this project!looks like you will be boating in no time flat.

Fired the motors today, they sounded good but have a sensor issue with the one...will most likely start a new thread

What boat is it?

2003, Warlock 31' SXT Cat

So I have been shacking out the gremlins one at a time and think I finally found the smoking gun I have been looking for. The video attached shows the fuel system tests, vacuum gauge tapped intothe pick up line between the fuel/water filter and the inline filter. Then a pressure gauge plugged into the fuel rail. I saw no issues on the pick up side as vacuum was under 1" Hg, however the fuel side has me troubled. When I crack the key, the pumps pressurize the system to ~48 PSI, but as soon as they shut off the gauge drops to 40 PSI. I start the motor and it idles around 40PSI, but as you can see when I tach the motor to about 4,000 RPM the pressure falls off to about 37 PSI :( No doubt this is a regulator problem, but do you think the pumps are suspect as well as the low 40 PSI is not being held or is there a normal range?

https://www.youtube.com/watch?v=0dn7j48WXsM

If those regulators are vacuum referenced the pressure should go down when you start it. Do both motors do the same?

yeah, I just ran the same test on the other motor and got identical results. When I pull the vacuum line to the regulator the pressure is a pretty solid at 45 PSI throughout the RPM range. Before putting new Merc regulators back in, anyone know who makes adjustable ones? My googling is coming back negative.

http://www.offshoreonly.com/forums/g...regulator.html

Have you contacted Raylar to get their recommendation on a regulator? He knows these motors better than anyone on the face of this planet. I don't really see the need for an adjustable regulator with the motors you are running. But I'll leave that up to the experts like Raylar.

You need to do the fuel pressure test under load. Your vaccum free revving to 4000 is not anywhere close to under load at 4000, nor are your fuel delivery requirements. Take her for a ride with somebody noting the fuel pressure and vacuum readings, then switch instrumentation to the other motor and compare.

First call was to Raylar, but they are out of the office this week. Matt, I just was doing some bench marking from engine to engine before finishing the break in, and was expecting a difference from one motor to the other (hoping for a smoking gun), even if not a real work environment...but sadly they are both the same. So I'm suspecting the the lower than expected PSI numbers are a result of this cheap gauge?. Many years ago I did have these ECUs flashed by Mercury as part of their tech brief dealing with transom soot....thinking maybe now I should have them flashed back?

Fuel PSI is correct. Its vacuum referenced and without load, it will not increase, it will decrease as the vacuum does.

Rewording since some made typos and to make this all clear -

As vacuum increases fuel pressure at the rail decreases.

As vacuum decreases, fuel pressure at the rail increases.

For fuel psi tests we like to:

Ck fuel psi with key on, engine off. (KOEO) Note fuel psi. There should be a Merc spec on this to compare.

Ck fuel psi with key on, engine running. (KOER) Make sure engine fully warmed up. Note fuel psi. There should be a Merc spec on this to compare.

Wide open throttle, full rpm. This is max fuel use as you are using max horsepower. Note fuel psi. This test is to see if fuel volume is adequate at highest use. If it isn't, the fuel psi will be falling off (going down).

====================

As others said above, and shown in your video (good vid by the way) steadily increasing rpm under a no load situation (on the trailer) doesn't require much throttle, thus the intake vacuum will rise causing your fuel psi to go down. This is normal.

People wonder why we use vacuum referenced regulators. It's because manifold installed injectors have their nozzles (spraying fuel) in the intake runners, which means they are subjected to manifold pressure/vacuum. This would change the flow rate of the injector (as manifold vacuum increases or decreases) as it's an opposing pressure.

So, the regulator being referenced to manifold pressure, keeps the acutal - at the nozzle - fuel psi constant.

Imagine trying to program a computer to constantly varying fuel psi ? Not gonna happen.

Again, not the fuel psi you see on the guage, as that will change - the actual psi at the tip of the injector.

Hopefully I explained that half way clear enough to understand and make the whole subject easier to understand.

Thank you all for your comments, they appear to be spot on related to vacuum regulated fuel pressure. This last weekend I did a series of benchmark readings with a tech in the back seat reading the gauge. From idle (40 PSI) to WOT the pressure would climb to 42 PSI then stabilize at 40 PSI until decelerating when the pressure would drop to 38 PSI. Based on what I see on these numbers, the fuel delivery system should be discounted as a potential source of my problems? Maybe I'm looking for a problem that isn't there (now), but this was the second motor in 12 years while the Port motor (450 hours) was still original. My next step is to remove the siphon tube, open the fuel tank to see if I have water or anything else that might be creating an intermittent problem. Suggestions always appreciated.

http://www.intored.net/media/496/fuel_press-tests.jpg