Mercruiser 5.0 tach issues need help on my 3rd one!!!

[broncodriver]

Had to replace the factory gauges (VDO only made 1 year for Bayliner one piece molded set with circuit card and not repairable (I sent them in)) on a 2001 Bayliner w/Mercruiser 5.0 engine. 1st one worked for 10 minutes and quit so I thought it was manufacture defect and swapped it out, the next one (this spring) worked for about 10 minutes again and quit. So, I thought it might be the boat wiring and I ran new wires from the ignition, ground and neg side of the coil to the 3rd tachometer.
All other gauges share this hot, lighting and ground wires all work without any issues. Again this tach worked for 10 minutes and quit.
Is there a resistor or something that I need? I'm guessing the coil keeps frying them? Fuse does not burn out, and yes the tach is set on 8C/4P, boat is all orginal factory, nothing special about the coil, not EFI engine etc.
Help this is getting expensive!!

 

[alldodge]

Had to replace the factory gauges (VDO only made 1 year for Bayliner one piece molded set with circuit card and not repairable (I sent them in)) on a 2001 Bayliner w/Mercruiser 5.0 engine. 1st one worked for 10 minutes and quit so I thought it was manufacture defect and swapped it out, the next one (this spring) worked for about 10 minutes again and quit. So, I thought it might be the boat wiring and I ran new wires from the ignition, ground and neg side of the coil to the 3rd tachometer.
All other gauges share this hot, lighting and ground wires all work without any issues. Again this tach worked for 10 minutes and quit.
Is there a resistor or something that I need? I'm guessing the coil keeps frying them? Fuse does not burn out, and yes the tach is set on 8C/4P, boat is all orginal factory, nothing special about the coil, not EFI engine etc.
Help this is getting expensive!!

:welcome: to iboats

What does VDO say about the issue?

I have VDO gauges and had to replace my fuel gauge, no issues

 

[alldodge]

Maybe the coil or ignition module is the issue, allowing to high a pulse going to the tach.

 

[broncodriver]

no I'm sure the coil is good the boat runs great less than 120 hours all original 1 owner boat, nothing special about the coil very car like looking black round old school oil coiled
sorry if I confused anyone on the VDO gauges that's what it came with and I had replace they are know to be junk and are extremely prone to the mother board failing replaced them with Mercury gauges http://forums.iboats.com/forum/boat-...es-not-working

 

[Scott Danforth]

mercury gets their gauges now days from VeeThree (old Teledyne marine gauges) you may want to also look at either the VeeThree website or the Teledyne website

 

[broncodriver]

here's the ones I have been buying http://www.marineengine.com/newparts/part_details.php?pnum=MER79-895283Q03

 

[alldodge]

Other then the 2011 post you listed I haven't heard of mush trouble with VDO gauges. As before I replaced my fuel gauge only because it was dragging and I have a 1995 with over 500 hours. Maybe buy another cheap VDO gauge which will last 120 hours, instead of the High quality Mercury gauge which last 10 minutes.

Iboats does like your link it turned it into stars

 

[UncleWillie]

Just a wild guess to throw into the pot....

The kickback from the coil is absorbed by the Capacitor across the Points. (Simple Explanation!)
The top of the Capacitor/Condenser is where the Tach signal originates.
If the Cap is not functioning, that energy has to go somewhere. The Tach is the next item in the circuit.

 

[alldodge]

Just a wild guess to throw into the pot....

The kickback from the coil is absorbed by the Capacitor across the Points. (Simple Explanation!)
The top of the Capacitor/Condenser is where the Tach signal originates.
If the Cap is not functioning, that energy has to go somewhere. The Tach is the next item in the circuit.

Very good point Willie, the cap is in the ignition amp with electronic ignition

 

[broncodriver]

to allDodge... I ment no offense to VDO gauges they are great but not these I speak of they are all one piece molded and not separate gauges they were only made for Bayliner and they are not something you can even get from VDO http://www.baylinerparts.com/2001/ca...Output/bk9.htm they may look like individual gauges but they where not just one big piece of plastic joined together on a motherboard.

I noticed when I turn on the ignition the tach does move to zero.

unclewillie I replaced the coil and cap tonight for the heck of it the old tach and 1 prior old one still do the samething move to 0 with the key on and do nothing with the engine running so I put in tack #4 I got in the mail today and it worked great for 3 minutes and went dead great I get to buy another one now
I'm going to try to tell the seller it was DOA or now I'm out another $88, and new cap and coil guess I have pleanty of spare parts

 

[broncodriver]

I hate to be defeated for something that should be so simple but I guess I have to bite the bullet and wait 3 weeks to get it in someplace

 

[alldodge]

I don't think it's the tach, IMO it appears to be the module. As previously posted, when the coil fires there is Electro Motive Force (EMF) which comes back across through the primary winding from the removal of the ground to the Neg side of the coil. This EMF should be absorbed by a capacitor which was in the distributer with a points system, the cap is now in the ignition module. If there is nothing in line which will absorb the EMF, it will go to the anything else attached to it. Not saying this is what's happening, just don't think it's a bad tach. If you had an oscilloscope you could see what is happening, without that maybe find the old style Acutron hand held tach and dwell meter to attach to it. I have one in my shop from years gone by, and they were built to a beefier standard

 

[midcarolina]

I may be way off here but if the condensor/capacitor is located in the ICM and is questionable if the cap is bad causing high frequencies ( killing the tach)

Couldn't the OP install a capacitor in the grey wire to prove a high freq. issue ?

 

[broncodriver]

ok here's what i found this should do the trick I think http://www.marshallinstruments.com/products/9219.cfm

Newest Tach arrived today still waiting for an opening at a repair place as this is #5 and I've got money into replacing the coil, distributor, and condenser which still fried tack #4

 

[broncodriver]

good news it's not me or the boat....it's the Chinese! apparently they are putting in 1/4 amp resistor and not a 1/2 amp resistor in the tach. Mercury is reimbursing me for all 4 I've bought and sending a new on that will work. . Must have an R listed at the end of the serial number and this issue is ONLY with 2001 carb Merc 5.0 with Thunderbolt ignition systems

 

[broncodriver]

now to run all the suggestion parts from playing swaptronics

 

[alldodge]

good news it's not me or the boat....it's the Chinese! apparently they are putting in 1/4 amp resistor and not a 1/2 amp resistor in the tach. Mercury is reimbursing me for all 4 I've bought and sending a new on that will work. . Must have an R listed at the end of the serial number and this issue is ONLY with 2001 carb Merc 5.0 with Thunderbolt ignition systems

Sure glad they got if figured out and the best part is they are reimbursing you.