Volvo Penta Tachometer Trouble

[westwon]

Hi all.

I'm an experienced technician, but this one's got me stumped. Just wondering what I've missed...
The boat is a 2003 Benetteau First 35.5 with a pretty standard setup. The old tach (PN 840866) slowly started to die, which suggests a corrosion issue to me, then died completely. Replaced the tach with a new one. new tach set up properly, but only goes to 1000 RPM at startup then goes to zero. Sent that tach back and got another new one. Exact same response, so it's not the tach. Measured AC voltage changing with the RPM at the 'W' post on the alternator so the alt is putting-out the required signal. Line from the 'W' to the tach has low resistance.
Now the weird part. The owner's guide schematic shows the 'G' (also called the S-) post on the tachometer going to a connector, BUT no wire coming out. I looked and found there IS a wire coming from the connector, but have no idea where it goes.
So I metered the good S+ (AKA 'W') wire at the back of the tach and used the S- as my ground. No signal.
I'm reasonably sure I have a S- issue here as I do know the signal is coming from the 'W' on the alternator.
Any guidance would be appreciated!

Steve

[DougR]

Engine model?

[westwon]

not entirely sure (it's my buddy's boat), but it's a 3 cylinder volvo.

Steve

[redbeard1]

Originally Posted by westwon

not entirely sure (it's my buddy's boat), but it's a 3 cylinder volvo.

Steve

Hi,
I did a quick google search on the boat name and volvo penta 2003 keeps popping up. Assuming that is the engine, and assuming you are using an exact oem replacement tach, the attached wiring diagram used on my 2003B may be helpful.

If you can confirm the engine and replacement tach, i might be of more use. Our boat had some tach issues last spring and I spent too much time getting familiar with the tach and wiring for my boat.

[DougR]

It's unlikely the engine is a 2003... These engines went out of production in 1993. More likely it's a 2030 or 2040, or outside chance it's a D1-30.

In any event, if the tach is alternator driven there should be the "w" terminal wire running from the alternator to the tachometer. It carries the variable frequency signal from the alternator to drive the tach. Although the tach has two signal leads ( s+ & s-) only one is used for alternator driven tachometers. The other wire (s-) is there in the panel harness for the use of other engines that use the same panel but instead of alternators they use two wire inductive pickups to drive the tach. The s- wire is in the panel harness and also the connecting harness to the engine, but it ends at the electrical box on the engine.

Testing for signal between the s+ and s- wires will not show anything.....test between s+ and ground.

Most likely the problem is that the new "universal" tach has not been set up properly. After you set the code number in the tach window for the engine model in question, you have to wait about 10 seconds to allow the window to revert back to the hour meter mode before turning off the power, otherwise the setting won't take. Then you can turn off the panel key.

Hope this is helpful.

DougR

[westwon]

Thanks Doug and Redbeard!
My buddy just confirmed the engine now. It is in fact a 2003. Maybe I got the boat manufacture date wrong.
I did try and get a signal at the tach using the DC ground that is there for the light and didn't get a signal that way either. Now the interesting thing is that this boat uses a sealed lighting and alarm circuit card to get grounds to the all the instruments. I can't help but think maybe this has something to do with the issue.
Redbeard, for some reason I'm not seeing your attachment.

Thanks again gents

Steve

[westwon]

Oops, sorry Redbeard. Your attachment is there, I just missed it. Actually I have that exact same drawing. Just because of the interaction between the grounds and the circuit card, I'm suspicious of it. Thoughts?

Steve

[coastalexplorer]

Westwon ..Steve.

I always thought that a Volvo Penta 2003 was standard issue on a Beneteau 35.5...I am as far from an electrical expert as you can get and thus have my own problems, So nothing to add to this one. except the choice of alternator manufacturer that Volvo chose for this engine was not liked by our local Vancouver based auto electric shop. it is also only 55 amp. So my engine has Remy Delco 110amp. IF you ever change to this the pulley has to be 76 mm out side diameter and the Vee belt profile has to match.

BTW If your friend ever has any problems with the damper connection between the engine and transmission, ( which is a common known problem)
I worked with Nextwave marine systems Inc on Vancouver's Island to make a Suredrive to solve it. Which is a bolt in swap. Stem to Stern marine on Powell street are stockists for it also.

[westwon]

Thank you CoastalExplorer! I'll let my buddy know. We are actually just south of Vancouver so know Stem to Stern well.

[DougR]

[QUOTE=westwon;2585775]Thanks Doug and Redbeard!

I did try and get a signal at the tach using the DC ground that is there for the light and didn't get a signal that way either. Now the interesting thing is that this boat uses a sealed lighting and alarm circuit card to get grounds to the all the instruments. I can't help but think maybe this has something to do with the issue.


Westwon,

The ground circuit for gauges and other functions on the panel doesn't come from the alarm unit, the ground wire enters the panel on pin 16 in the harness and originates on the engine. If you can't find a tach signal on the tach s+, but do have the signal at the rear of the tach, then it follows that there is a problem in the S+ wiring to the panel or possibly in the ground lead to the panel.

DougR

[westwon]

Thanks Doug.
I did meter the lead from the back of the alternator ('W' or S+ pin) to the back of the tach, and it's only about 1.5 ohms, so it's good. I have to agree with you that I probably have a grounding issue. I know from previous experience that ground issues can cause some weird and wonderful snags!

Thanks again

Steve