Strange Change on RPM's - any ideas?


toofast said:
CMac said:
You can use a simple old timing lite to check power to the plug. Clip it to each wire as close to the plug as possible to see it blink per fire.

Bet it's a plug, they can look good, but be failing intermittently.
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Dumb question...will the timing light catch a bad plug, or only if it is completely "dead" i.e. getting no spark? Just curious if I should invest in that, or simply just replace every plug, even though when I pulled them before they all "looked" good.
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The lite is only going to test each coil and wire to the plug. I would put a fresh set in if you haven't already.
 
So you guys are gonna kill me...

If you followed this, I checked the plug wires, connections, fuel filter, battery, ground, props, etc.....still no fix.

Decided to change the plugs...first two look perfect...hard as hell to change...but they look good.

Third one is a bitch...put I get it...wires look fine.

However, as I am putting the wire back on, I felt a slight something...so I decide to remove the entire wire...and damn it..there is a crack and I could tell it was shorting every once in a while...so there is my problem.

Next problem is now that I removed it, it cracked completely, core is separated...so now I need a new wire. NONE to be found locally...does anyone know if the 496 Wire Set from a similar equiped Chevy 3500 496 will match up? Or at least be close enough?
 
best bet is to replace the entire set of wires.either go merc or siera as those are actualy merc wires.if one is bad,the others are not far off.
 
man spark plug wire kits are $350 for the after market sierra...and no where to find locally. Looks like to labor day boating for me :-(
 
toofast said:
So you guys are gonna kill me...

If you followed this, I checked the plug wires, connections, fuel filter, battery, ground, props, etc.....still no fix.

Decided to change the plugs...first two look perfect...hard as hell to change...but they look good.

Third one is a bitch...put I get it...wires look fine.

However, as I am putting the wire back on, I felt a slight something...so I decide to remove the entire wire...and damn it..there is a crack and I could tell it was shorting every once in a while...so there is my problem.

Next problem is now that I removed it, it cracked completely, core is separated...so now I need a new wire. NONE to be found locally...does anyone know if the 496 Wire Set from a similar equiped Chevy 3500 496 will match up? Or at least be close enough?
Click to expand...


Great find. Your boat is so new, I would think replacing the one wire would be ok. I also think the chevy 8.1 set would fit. You can also make your own custom ser. You just need some crimpers for the ends. However, niether may be marine grade safe. Not sure there's a difference.
 
As a quick update...there was not getting the right wires in time for the weekend. The ones off the same block, i.e. 2007 Chevy 3500 2WD, seemed to make the most sense, Autozone had them in stock, the ends were a match, but the truck wires were WAY to short...since they have the coil packs below the exhaust. Lucky for me, the local Autozone guy had some experience....he found a 1998 Chevy Dump Truck, that had a 454 block that he thought had similar ends....

Sure enough they did, and they were plenty long enough...so I made do just changing the one wire. All my power was back, RPM were perfect in sync again and fuel mileage was right on.

So my LONG story is almost over....now I just gotta get the right wires as the replacements were a bit skinny, and for long term I want the real stuff.

Thanks to all that helped...maybe someone else has a similar issue, as I missed the cracked wire the first two times I inspected them...
 
JEDD,
GLAD YOUR LITTLE PROBLEM DID NOT SPOIL YOUR HOLIDAY WEEKEND. WOULD HAVE BEEN A SHAME IF YOU HAD TO SPEND THE ENTIRE WEEKEND AT THE DOCK. ENJOY.
 
Yep, it was a great weekend...first really great weekend we had all summer.

Now we have to start thinking about winterizing...I hate the weather!
 
Winterizing? What's that??

Just jokin'. I do winterize the plumbing!

Great to hear you had a good weekend.
 
I had issue with starboard engine rpms running higher than port then stalling
boat sat for a few days. Ran quick with mechanic n no issues
went out yesterday came on plane and cruise at 3600 with no problem
idled a bit and when I powered up starboard engine
home on port. Starboard sounds like starving for fuel
saw comment on clogging fuel filter. First step
no errors shown for first issue
31 pc 2005 horizon salt water
 
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