Mercruiser 5.0 Tachometer troubleshooting: request advice

[mcginnal]

Hello all,

First, my boat:
2003 Monterey Montura LS 248
Engine - Mercruiser 350 (5.0L)

Recently purchased from previous owner with the tachometer not functioning. I have been paging through the engine owner's manual with not much luck on where to start troubleshooting. How would I determine whether the issue is the sending unit or the gauge?

Any help would be greatly appreciated; thanks.

-Alex

 

[Bosunsmate]

Re: Mercruiser 5.0 Tachometer troubleshooting: request advice

Hi probably best you ask in the Mercruiser section
Mercruiser I/O & Inboard Engines & Outdrives

 

[mcginnal]

Re: Mercruiser 5.0 Tachometer troubleshooting: request advice

My bad.. This thread was meant for that forum :lol:

 

[Fun Times]

Re: Mercruiser 5.0 Tachometer troubleshooting: request advice

Is this a carbureted or fuel injected engine model? Is your engine serial number handy?

Have you tried tapping on the gauge a little bit to see if it will unstick?

On the back of the gauge, there may be a little dial switch with an arrow pointing to some numbers. Try turning it a few times landing 8 cylinder. You may have to push in a little bit, if so make sure it pops back out.

 

[SWD]

Re: Mercruiser 5.0 Tachometer troubleshooting: request advice

Is this a carbureted or fuel injected engine model? Is your engine serial number handy?

Have you tried tapping on the gauge a little bit to see if it will unstick?

On the back of the gauge, there may be a little dial switch with an arrow pointing to some numbers. Try turning it a few times landing 8 cylinder. You may have to push in a little bit, if so make sure it pops back out.

This fixed my tach issue.

 

[QC]

Re: Mercruiser 5.0 Tachometer troubleshooting: request advice

Actually probably belongs in Electronics, but I moved it to Mercruiser. Poor thread topic without a real home . . .

 

[mxcobra]

Re: Mercruiser 5.0 Tachometer troubleshooting: request advice

a 350 is a 5.7

 

[mcginnal]

Re: Mercruiser 5.0 Tachometer troubleshooting: request advice

Is this a carbureted or fuel injected engine model? Is your engine serial number handy?

Have you tried tapping on the gauge a little bit to see if it will unstick?

On the back of the gauge, there may be a little dial switch with an arrow pointing to some numbers. Try turning it a few times landing 8 cylinder. You may have to push in a little bit, if so make sure it pops back out.

Argh, the plight of a n00b on his first boating forum. Forgive, me all!

It's the Multi-Port Injection - 305* cu. in vice 350 (S/N 0M646536). I will try this tip first, then start working my way back to the coil.

 

[QC]

Re: Mercruiser 5.0 Tachometer troubleshooting: request advice

BTW, multi-point 305's (5.0) have more horsepower than stock, carbed 5.7s ever did. You're all good.

 

[mcginnal]

Re: Mercruiser 5.0 Tachometer troubleshooting: request advice

Just a follow-up question: I'm about to open up my dash to fix this tach. Assuming the above recommendations do not work, would it be worth checking continuity from the coild to the dash? I was thinking of checking voltage via multimeter at the leads that attach to the actual gauge. Only thing is, I'm not sure if the coils send a DC signal proportional to the engine speed, or an AC signal w/the frequency of whatever RPM the engine is at, etc. Any ideas would be awesome.

 

[mxcobra]

Re: Mercruiser 5.0 Tachometer troubleshooting: request advice

My guess is the signal sent to gauge is in ohms, I would def. check the wire for continuity. then check if ohms change apon reving up your 305 ") if ohms do change then the gauge is probly cooked
sory didn't mean anything snooty earler........
good luck.
I do know when I was fighting with my gauges the problem was indeed the wire pulling out of its clip!

 

[mcginnal]

Re: Mercruiser 5.0 Tachometer troubleshooting: request advice

My guess is the signal sent to gauge is in ohms, I would def. check the wire for continuity. then check if ohms change apon reving up your 305 ") if ohms do change then the gauge is probly cooked
sory didn't mean anything snooty earler........
good luck.
I do know when I was fighting with my gauges the problem was indeed the wire pulling out of its clip!

No offense taken

So I crawled behind my dashpanel this weekend. I have power supplied to the tachometer from the batter (multimeter was reading 12V DC). I checked all connections and they looked fine. I've been doing some hardcore googling, and found a good resource from Faria on tachometers:

Source: http://webcache.googleusercontent.c...er+electrical+signla&cd=1&hl=en&ct=clnk&gl=us

The sensing line (gray line) should read in excess of 2V DC while the engine is in operation. Now that I know this, I'm going to see if it's a sensing line issue or if the tachometer is burnt. At any rate, thanks for the ideas!