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Tachometer Trouble

Big D

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New to us boat, 2002 Chaparral Sunests, has a Volvo Penta 8.1 & the dual prop out drive. Tach isn’t working and was told that it was a bad tach. Replaced it with a new autometer & still having issues. When you turn the key on, the tach responds but does not go to zero. With the engine running it just bounces around and does not seem to respond to engine RPM. Wiring is pretty basic, ground, hot line from key & wire from sending unit. Any idea what could be causing the issue? Should the wire from the sending unit show power when the engine is running?
 

Lavey 29

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the crank sensor provides the tach signal for the tach on all OEM stock 8.1 s / 496s. Change that and also Check the connector at the crank sensor as well because many boat engine hatches back edge are a straight shot down that can be water drip line right into the connector and or on the crank sensor itself .
 
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Big D

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the crank sensor provides the tach signal for the tach on all OEM stock 8.1 s / 496s. Change that and also Check the connector at the crank sensor as well cause because many are a straight shot down from the back edge of the engine hatch cover that can be water drip line right into or on the connector and crank sensor.
Thanks for the feedback! Is that sensor on the flywheel or dampener end of the crank?
 

Lavey 29

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no offense it would be wise to buy an oem shop service manual if your going to work on your own apps. Think about if the ac guy is there to fix your home ac unit would nt you want him to be trained and or at the very least have read the service manual for your ac app ? Again no offense as I am giving out solid advice here for all boat owners about manuals and proper tools to be able to perform proper work on a boat / engine instead of winging it and an expensive guess as you go parts changer in which is very costly..

It would be wise to scan the engine as well. Engine serial number is very important plus that will determine engine set up / parts installed and procedures and which ecm is installed for the correct adaptor using the scan tool plus the data / parameters on the scan to monitor. Volvo is NOT Mercruiser nor set up like one. Totally different PCM s among a lot of other things. I can not stress enough how important engine serial numbers are in the marine world. Number one info to have hands down regardless for OEM stock marine engines.

Anyways the crank position sensor is located on the top back side of the engine. There is a gen 1 version ribbed and the later gen 2 non ribbed version as they are a long pencil style sensor but not as skinny as pencil. Penny size diameter -- 8 inches long and one bolt mount. 3 wire connector on top..
 
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LOBOATOMY

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John, good to hear from you. I've been giving them hell about you over the other side of the hill.
Thank you for all of your knowledge contributions.
Gary
(Sorry about the hi-jack)
 

Big D

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no offense it would be wise to buy an oem shop service manual if your going to work on your own apps. Think about if the ac guy is there to fix your home ac unit would nt you want him to be trained and or at the very least have read the service manual for your ac app ? Again no offense as I am giving out solid advice here for all boat owners about manuals and proper tools to be able to perform proper work on a boat / engine instead of winging it and an expensive guess as you go parts changer in which is very costly..

It would be wise to scan the engine as well. Engine serial number is very important plus that will determine engine set up / parts installed and procedures and which ecm is installed for the correct adaptor using the scan tool plus the data / parameters on the scan to monitor. Volvo is NOT Mercruiser nor set up like one. Totally different PCM s among a lot of other things. I can not stress enough how important engine serial numbers are in the marine world. Number one info to have hands down regardless for OEM stock marine engines.

Anyways the crank position sensor is located on the top back side of the engine. There is a gen 1 version ribbed and the later gen 2 non ribbed version as they are a long pencil style sensor but not as skinny as pencil. Penny size diameter -- 8 inches long and one bolt mount. 3 wire connector on top..
Thank you for the input. I've searched for the serial number but can't seem to locate it? Any advise on where it can be located?
 

Fun Times

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Edit: So Sorry @Big D , I totally gave you the wrong engine info in here late last night.... I swore I thought I had read you had a Mercruiser somewhere along the line or I guess I just started assuming I did anyways without rechecking...Usually that's not me..:oops: I digress..

If you can't locate a engine serial number then sometimes it could be helpful to post your Transom assembly and stern drive assembly serial numbers as some here such as Lavey 29 could also try checking the registration history for any other past Engine/Drive/TA serial number application match ups should it deem necessary.

Though you've been here for a bit already, Welcome John and sorry to see of the situation over there too.:(
 
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Lavey 29

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Also thanks guys for your comments. Gary we are good and thanks as well. God forbid I help out anyone over there. Gary knows as I even gave out my phone number as well for help all the time.
 

Big D

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Thank you all for the great info! Much appreciated!
 

DaveH

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while the 8.1 from the factory have a known issue with crank trigger failures........the crank trigger doesnt provide a connection to a tach.

i dont know volvo electronics......but any and all efi systems have a tach output from the engine computer, NOT the crank sensor.

for the record i'd bet its your tach thats bad.
 
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