MORE 496 HO PROBLEMS

[goldeneyee]

I'm absolutely positive that there is a black cloud over my head following me around! Boat is in fresh water and about a month ago the port engine wouldn't RPM over 3200. After much digging it was a Denso plug issue and replaced all with AC and ran fine. Let it set for a month without using and same problem--performed Rinda cylinder drop test and was number 8 cylinder. Replaced plug with new AC and still no power--old plug looked like new. Pulled plug wire and sure enough getting plenty of spark. Put a new injector in and still no power out of 8. Didn't have compression tester with me. This spring I removed turbulators and I have that sinking feeling in the bottom of my stomach that water may have dripped down and rusted the exhaust valve in #8. Engine is a 2003 with about 46 hours on it. Seems to idle fine--no backfiring. Can't really listen to exhaust as it exits under a solid swim platform. My only other thoughts are a bad wire to the injector or a pcm 555 issue. Looking for an expert opinion. Thanks.....

[Boat Tech]

Just for a quick test, you could try switching your two PCM's around between the two engines.

[goldeneyee]

Thanks for the reply. Probably a good suggestion. Have there been problems with the pcm 555? Boat is a 2003 but motors were built in 2002.

[goldeneyee]

Just returned from the boat. Did a compression test on #8 and I was shocked! 160 psi. Reinstalled spark plug and decided to go through the Rinda testing of injectors, coils, etc. Instead of attempting to disconnect both the low and hi pressure fuel pumps, I shut the gas valve off from the tank. Individually tested #8 and well as group tested injectors . In the coil testing got a backfire--I assume from 8 as there was residue fuel squirted in from the rail. Found nothing--no codes or faults. Fired engine back up again and performed the drop cylinder test a half a dozen times and guess what--#8 was now firing and dropped each time I performed the test. The only abnormality I found was a couple of times I left the throttle at 1500 and a few minutes later the rpm would mysteriously rise to 1800 without touching the throttle. A choke issue or was that cylinder cutting off and on again--never happened when I was doing the testing. To say the least, I'm beyond perplexed.....

[Laredo]

valve spring?

[goldeneyee]

At this stage I'm thinking more of an electrical gremlin--coil, bad ground, chafed wire, loose or corroded electrical connection, etc. However, I have an open mind and certainly would entertain all suggestions...

[OneBadInjun]

At this stage I'm thinking more of an electrical gremlin--coil, bad ground, chafed wire, loose or corroded electrical connection, etc. However, I have an open mind and certainly would entertain all suggestions...

How did things works out? Curious to know if you discovered what the fly in the ointment was. thanks

[goldeneyee]

I had to take the boat out of the water for winter storage. Running across the lake for 10 minutes on the way to pull it out, it ran on all 8 then dropped a cylinder for the balance of the trip. Over the winter, I'll dig into it more, however, I'm convinced its electrical. One strange thing, I think I had an alarm go off--could have been a depth sounder but if so, Rinda would bring up. I certainly will follow up when I find the cause of the problem......

[jrfriend1]

I had older corvette that dropped a cylinder or 2 ,found 2 injectors after heating the
the windings would open up.

[ROGUE]

I love my old school, carb, 1 wire engines.