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Tach jumping around!!! Any ideas?

Dirty Daytona

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Maybe someone can help me with this issue. 2006 27 Daytona with a carbureted big block chevy. Standard 2 wire distributor, mercruiser coil, pretty basic setup. My problem is 1/2 throttle and above the tach goes apeshit and jumps all over. When this is happening the engine is running perfectly and the RPM’s are NOT fluctuating as the tach is showing. This does not happen on the hose in the driveway, only under a load on the water. The tach is an analog Pro comp. Any ideas of what could be going on?
 

Riverbottom

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My ski boat just did this last week. I took all the terminals off at the tach and sanded them clean and reinstalled. I also removed the terminals on the coil and cleaned and reattached. Problem solved. Hope yours is that simple.
 

Dirty Daytona

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My tach doesn’t have terminals, just 4 wires coming from inside of it. I will try the coil wire also. I was thinking about trying to just run a whole new wire from the coil up to the tach and see if that fixes it. Thanks for the help!!

My ski boat just did this last week. I took all the terminals off at the tach and sanded them clean and reinstalled. I also removed the terminals on the coil and cleaned and reattached. Problem solved. Hope yours is that simple.
 

4Waters

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Maybe someone can help me with this issue. 2006 27 Daytona with a carbureted big block chevy. Standard 2 wire distributor, mercruiser coil, pretty basic setup. My problem is 1/2 throttle and above the tach goes apeshit and jumps all over. When this is happening the engine is running perfectly and the RPM’s are NOT fluctuating as the tach is showing. This does not happen on the hose in the driveway, only under a load on the water. The tach is an analog Pro comp. Any ideas of what could be going on?
I'm going to say it's your ground
 

Not So Fast

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Check the ground !! Mine acted funny and the maker said it needed a filter which they sold me, fixed it :cool:
Bobby V
 

572ext

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What kind of distributor is it m s d is the distributor the same one or has it been replaced if it’s been replaced did the problem start if it’s m s d They make a filter for it
 

Nanu/Nanu

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First things first did you check your prop torque...

Jk I agree with checking grounds. Or connections first.
 

Dirty Daytona

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What kind of distributor is it m s d is the distributor the same one or has it been replaced if it’s been replaced did the problem start if it’s m s d They make a filter for it
It’s not an MSD.
 

Nanu/Nanu

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On a serious note. Check all your spark plugs caps or coil packs what ever you have. I had one come loose on my number 7 cylinder once and after about 10 minutes the tach would start bouncing.
 

monkeyswrench

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I don't know what the distributor is, but assuming a magnetic pickup or hall effect modern deal. I've had two issues (not counting an angry MSD box) One was a dirty vent, causing a build up of ionized air, but it would only start to be an issue at higher rpms, and after running a bit. The other was the upper bushing going to hell, and sending tiny stripper glitter into the pickup area. Both didn't do anything noticeable to the actual spark.
The first one was a mother F'r to figure out!
 

Dirty Daytona

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I don't know what the distributor is, but assuming a magnetic pickup or hall effect modern deal. I've had two issues (not counting an angry MSD box) One was a dirty vent, causing a build up of ionized air, but it would only start to be an issue at higher rpms, and after running a bit. The other was the upper bushing going to hell, and sending tiny stripper glitter into the pickup area. Both didn't do anything noticeable to the actual spark.
The first one was a mother F'r to figure out!
I appreciate the suggestions, tomorrow I will pop off the distributor cap and take a look.
 

Dirty Daytona

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On a serious note. Check all your spark plugs caps or coil packs what ever you have. I had one come loose on my number 7 cylinder once and after about 10 minutes the tach would start bouncing.
I will check them again for sure!!
 

Ricks raft

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On one of my older boats, tach intermittently was erratic. don’t remember which brand, it had a switch for 4/6/8 cyl. Contact cleaner on switch it.
 
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