liquid asset

I have had my 500efis for 3 years the first 120 hours they were perfect. Then a rod pulled out of a piston at 4000 rpm and it was trashed had a reputable marine tech completly rebuild it top to bottom at considerable expense now 12 hours later it has dropped an exhaust valve seat and has to be redone again due to what he calls detonation he says all of the exhaust valves got so hot they tuliped. Now he says it is because of the gas which I purchased from exxon supreme 93 octane which is what I have always used. I have friends with 500s that say they never run 93octane only 87 and have 500 hours on them. Everybody says these motors are bullet proof. So has anyone had any trouble like this I feel like it had to be a lean condition ie fuel pump injectors, computer something other than the gas. ANY HELP WOULD BE APPRECIATED THANKS

SteveDavid

Liquid Asset,

87 Octane is all you need, but 93 should not cause what you experienced. The higher Octane has a slower burn rate and would generally cause a more rich condition, rather than lean. The computer on your 500 EFI, I'm guessing by it's age it's a MEFI 3, would either shut down or cause a low RPM run if it sensed a lean condition or low fuel pressure, unless the ECM is going bad, and that's RARE. Have a merc mechanic use thier Scan Tool and search for fault codes. That should lead to the problem. Have you pulled a couple of spark plugs, and if so did they indicate a lean condition? If the Scan Tool shows no fault codes, you can pull your injectors and send out to be flowed. If any are partially clogged that could be the problem, but the engine's knock sensor should have caught that which then retards the timing and drops your RPM. Did you notice a drop in RPM before this last "incident"?

If this all sounds like greek, (and you're not greek) feel free to call me Monday at 954-565-0014 and I'll walk you thru the process.

Steve

SteveDavid

Liquid Asset,

87 Octane is all you need, but 93 should not cause what you experienced. The higher Octane has a slower burn rate and would generally cause a more rich condition, rather than lean. The computer on your 500 EFI, I'm guessing by it's age it's a MEFI 3, would either shut down or cause a low RPM run if it sensed a lean condition or low fuel pressure, unless the ECM is going bad, and that's RARE. Have a merc mechanic use thier Scan Tool and search for fault codes. That should lead to the problem. Have you pulled a couple of spark plugs, and if so did they indicate a lean condition? If the Scan Tool shows no fault codes, you can pull your injectors and send out to be flowed. If any are partially clogged that could be the problem, but the engine's knock sensor should have caught that which then retards the timing and drops your RPM. Did you notice a drop in RPM before this last "incident"?

If this all sounds like greek, (and you're not greek) feel free to call me Monday at 954-565-0014 and I'll walk you thru the process.

Steve

bikinilover

When did you get 500s? Just kidding! I heard what happened. I bet he is pissed.

ursus

When the injectors sit they dry out and get varnishised up from residual gas that evaporates. This isn't a problem in the winter because when you winterize you add 2 stroke oil and stabilizer to the gas and run for a few minutes to prevent this. When an engine pukes tho this is not done and if the rebuild takes a while then you get injectors that don't flow what they should and a lean condition. I was lucky some of the injectors actually plugged up completely so the condition was obvious) . 93 octane gas,will not do this and in fact the ecu does a knock check by advanceing the timing momentarily on start up to verify the knock sensor is functional. The test often fails with 93 octane ( because the engine doesn't knock) and the ecu actually puts it in rich /timing retarded mode. Othere posibilities the fuel preasure wasn't right or restricted via a filter with crud etc or a bad ecu.

And "reputable marine tech " would know 93 gas does not cause a lean condition and in fact the engine would be less likely to denotae not more.

liquid asset

Ursus

The motor ran fine for 12 hours if it was the injectors would it have run for that long?
The tech says I put bad gas in the boat meaning low octane fuel. I know I put in 93 and that is all I can do. He just dosen't want to warranty the motor also it tulliped all of the exhaust valves on one side if it was injectors wouldn't it be just one or two cyclinders.

red thunder

Rebuild at considerable expense should of included a dyno run and a warranty.

28Eliminator

Just a thought! Maybe it wasn't put together right and had a vacumm leak on the intake causing the lean condition. Did they rebuild the heads and install Inconel valves or did they install regular valves used in cars. Did they install new seats wrong causing the seat to dislodge. Seats shouldn't fall out and if that is what happened, the machine shop is probably to blame. Lots of unknowns here. You need to do somemore investigation.

liquid asset

Did include dyno run and warranty but what do ya know detonation is not covered as far as valve seats the story is they got so hot from the detonation thats why they fell out as far as a vaccum leak boat ran perfect up until time of damage.

Boatfixr

Check for exhaust restriction on the side that tulipped the valves. Maybe a sticking exhaust flap or bad silent choice valve if you have them. Water flow restriction or steam pockets in one side can overheat the cylinder head, causing your problems. IMO bad gas is not the culprit. You can always send a sample to a lab to confirm the octane. FIND the cause before running a new engine or a repeat can happen. Do a flow test on your fuel tank at the feed hose and be sure that the vent is not clogged or hose kinked. Double check all cooling system components and plumbing.