Any ideas what could cause it? I have scanned the computer(s). No codes beside the normal non smart craft codes. Seems like it is loosing power or something along those lines.

Normal wiggle test of the kill switch dose not result in anything.

Dealer has replaced IAC, TPS, 50 amp breakers, and $1800 ECU! One of the engines that have also replaced the fuel pump. Fuel filters are fresh.

2006 496 HO. Last scan was 370 hrs. Seems like it is looking power or something along those

Watch around 19 - 25 seconds on the video.

Some days it will do it 1 time. Other days it will do it several.

https://www.youtube.com/watch?v=YjpOWyRCmk0

Clean, tighten and/or replace all the battery terminals.
Clean, tighten and/or replace the grounds on the back of your bell housing there is 2 on each engine bell housing.
There is an actual ground block that is on the transom, clean & tighten.
If this fails try this - run your batteries as 1 and 2 not "Both" - see what happens.

FWIW - If a dealer didnt check those things first, I would be PISSED! If you do the above, I bet you either fix or find your problem.

I know it sounds illogical but if your batteries are old and lose charge relatively quick, replace them. As soon as my last set of AGM batteries got old they did some crazy stuff.


I'm still pissed at your dealer, and you should be too!

I saw (internally) broken/failing wires on the back of the key switches cause this once on a boat with 525s.
I'd also go ahead and replace the Crankshaft Position Sensor if it hasn't been done; and before you actually do that, make certain that your connector/connections to the CrankPS are all in sound condition.
BUP can confirm. The tachometer signal comes from the Crankshaft Position Sensor IIRC.

Sounds like the problem is around your ignition switch

It appears to me no other gauges flickered/moved when the tach went to 0, is this correct ?

Here is a wider shot of his video showing all gauges.

https://www.youtube.com/watch?v=YjpOWyRCmk0

Agree with Sydwayz. I had the same thing happen in my 2001 Chevy 496 equipped truck. Did it randomly for almost a year until finally crank position sensor went out completely.

Correct. only the tach. and the beep. But it only turns off for .5 seconds so the other gauges probably don't have time to turn off?

Thank you guys! I do not remember if they replaced the CPS or not. Ill have Steve look it up in his paper work. This is a good boating friend's boat. He has been round and round and round with the dealer on this. So I told him I will help him out. F@#* the dealer.

Little back ground. Last time it was in for this (July) they somehow ****ed up a fuel pump and the computer.

Dropped it off for this issue Monday, they threw a few parts at it and he picked it up late Friday after they supposedly water tested it. When out the Saturday morning, both engine would not start at the dock. (boat is trailer'ed ) Back to the dealer Monday morning. One engine had a fried fuel pump (star), the other fried computer (port) IIRC .

what I seen = No other gauge LOST power period Just the TACH - with that said if it was a connection from the batteries - back side engine grounds, cannon plug in, key switch - kill lanyard then we would see other areas losing power as well NOT just the TACH.

The tach receives its signal from the crank position sensor --- places to check first and foremost -- the crank sensor and the connection. The connection even if it has the slightest bit of moisture in it can cause problems. Check for corrosion as well and or shorted as well.

Replace the crank sensor. The NON ribbed crank sensor are way better than the older ribbed ones. You should have the NON ribbed crank sensor. But they can still go bad but not as much as the first GEN ribbed ones.

Next the tach itself can be going bad ---- then the wires to the tach and or any related as a jumper wire(s) going from the tach to whatever ---- loose or corrosion or shorted for it.

Next ignition coil(s)

Next SPARK PLUG WIRE(S) / or its boot(s) spark arc off of whatever, Also make sure all are tightly pressed down all the way to

ALSO crank sensor fault does not show all the time either.

Also lastly the cam sensor works in conjunction with the crank sensor so do not rule out the cam sensor and or its connection.

Alot of parts changers out there..iac. tps and a processor..someone could have saved you a ton of money..what better way to do it than on a boat with twin engines.wouldn't it have been smart to swap the 1800 processor with the one from the other engine?.with that said....I have a remote Guage cluster ,key switch set up in a suitcase which will eliminate that engine from the entire rest of the boat..is it possible you can find a shop with good diagnosing tools instead of one that changes parts..if not.. doing a wiggle test doesn't really confirm that switches have an internal open in the switch..my point being that you can still have a bad ignition switch and kill lanyard switch. I would also jump the breaker on the motor because mercury has had a Ton of problems with the yellow flag style and went back to the red push button.once again get a set of jumper wires no need to just throw parts at it..don't forget about the main power relay..I have seen them cause similar problems..swap it with the one from the other engine but look at the terminals before you plug it in..ALSO don't only think of this as being a 12 volt issue..you could have 5 volt reference issue...that motor needs to be scanned while it's running and don't even bother looking for codes the problem can be found in freeze frame..