Tach Help/Info

[MMosher]

Ok folks my tach finally crapped out on me. Did all the trouble shooting things you're supposed to do and I think it's just dead. Looking for a replacement but they don't make the 0-8000 RPM Teleflex Red Domed gauge part #72288 (that part # is now a 6000 RPM Gauge). The only one I found that "looked" similar was the Teleflex Red 0-8000 RPM #53743. Should I take a chance with the "close" one or just replace it with the 6000 RPM gauge. I don't for see me breaking 6000 RPM anytime soon in my set up but would like to have it as close to factory as possible. This is my first tach replacement and I know NOTHING about em. A tach's a tach Right?.....

[DaveH]

I had a lot of trouble a few years back finding the domed one with the right bezel, I'll look though my receipts and see what I can find out

[95202DCX]

Teleflex Amega Gas Tachometer - Star Marine Depot

[Tx Champ]

Matt, first swap your tach lead (gray if my memory serves me) from the voltage regulator it's on to the other. That ended up being the issue on mine after I bought a new tach

[MMosher]

^ Not sure I'm following ya. Explain a little more please.

[Tx Champ]

The Merc EFIs have 2 voltage regulators. Each has a lead for the tach, which is connected to one of them. My tach would jump from zero to over 6K while running across the lake. Sometimes I would look at it and it would be at zero. So, I bought a new tach. It did the same thing. On the Merc forum, someone told me to check the VR. I pulled the cowl and was checking to make sure all my grounds were tight and the other connections when I noticed there were 2 of them. So, I made me a jumper (about 6") to chabe the tach lead over to the other VR. Boom, solid as a rock. Replaced the VR and all was well with the world. Also improved my voltage at the console, measured on my graph.

[MMosher]

^ Good to know. Thank you.

[02champ]

If tach reads rpms but they are abnormal and jumping all over the place then the VR is the place to look. Tx champ might know but i believe those VR's are pretty pricey so I'd make sure to figure out which one is the culprit first.

[jb7725]

I had the same problem on my efi. Check your voltage regulators on the back of the motor in between the coils for the spark plugs. Check every wire for burnt wires at the bullet connection. They will be brown or black if burned. Then pull both the regulators off and check them for burnt spots. If any burning is observed you MUST change the regulators is PAIRS. Cost me roughly $500 for the parts, was an easy job. If you can't see any burnt spots you have to measure your voltage at your cranking battery with your motor running, anything over 14.7 volts and your regulators are bad. Use a multi meter to measure voltage at the battery, don't trust the gauge for this.

[Bruce2]

Also if tach is jumping around pull tach out and look for POT switch and notice position and turn it back and forth several times...this cleans the contacts and set pot back to original setting..did this on mine and it helped alot. By the way my 1995 135 merc carburated motor has 2 voltage regulators also and gray wire is tach wire.

This is about as close as i have come to matching my tach...http://www.wholesalemarine.com/amega...by-sierra.html

[MMosher]

Good info everyone thanks.

[MMosher]

Well I pulled the cowling and checked the VR's....burnt wiring. Lovely. What causes this and how do I avoid this in the future? Almost positive that they are the original ones. Do they just wear out? When replacing this is there anything else I should replace while I'm at it? I'm no gearhead by any means so can the average joe fix this with the basic tools or do I need anything special? Looks like I'm boatless shore trash for a few weeks. Just in time for deer season. Also gonna post this on the Mercury Forum and talk to Don. Thanks for the info, you guys saved me a bunch of heartache.

[Tx Champ]

Burnt wiring doesn't sound good ... pix?

[MMosher]

Pretty much a carbon copy of this picture.
http://www.bbcboards.net/mercury-mot...efi-175-a.html

[Batman1977]

In addition to the regulators make sure your starting battery is a true cranking battery. Using a deep cycle can cause you burnt wires too.

[jb7725]

A deep cycle battery can cause this issue as it has a higher resistance to charging. Also very important that you use stainless nylon lock nuts on the starting battery post NOT wing nuts. When replacing the regulators, replace them in pairs. Also will need to replace the burnt bullet connections on All the wires, only thing you need is a pair of crimpers to do the job.

[jb7725]

2 regulators and the necessary bullet connections was roughly $500 shipped from don

[Bruce2]

I would pull all main positive wire off and clean them and also pull all negative wires off and clean them both at the motor and at the battery...I just did my main + and - wires on motor and battery and they had some kind of white stuff on them and when i took a wire brush on a drill and cleaned them looked like a white powdery stuff came off....just a thought.

[MMosher]

Thanks for the info everyone.

[MMosher]

Update: Parts arrived, installed and back on the water. Pretty straight forward but can't say I wasn't nervous on the test run this morning. Ran the piss outta her and she's good to go. Thanks for everyone's help. Special thanks to Reggie for his spare tach it was very appreciated. Hope I can return the favor to ya some day.