Eratic Gauges
 

I have had my boat out twice since I bought it in February , when I first took it out I noticed that both tachs fluctuated 500 rpm when running and both gas gauges did to. I took it out weekend before last and done the same thing this time the starboard tach was reading 500 rpm higher and it was still bouncing like the port along with the gas gauges. I do have one battery not holding a charge but that shouldnt effect both tachs since they are isolated power wise from each other. Any thoughts, common ground maybe?

Ground

Bad plug wires

Wouldn't bad plug wires cause the engine to miss? When it does this both engines sound in synch with one another and no sign of miss fire?

You've most likely got a ground short. Check the grounds at the fuel tank sending unit.

No you do not have to have a miss. A good friend with a 25 Eliminator fought this problem for days and finally changed the plug wires and it went away instantly. He told me about it when I had a similar problema nd I changed the wires and all was good and I did not have a miss at all. Sorry I do not know why or how to explain it. Just a suggestion based on experience.

Did those erotic gauges cost extra??? Just kidding, the battery will cause some crazy sh*t. Replace that before you go looking for trouble.

Ditto start with the battery, check the grounds and then go for the plug wires.

Could you explain this, cuz if it was shorted to a positive leg it would blow a fuse or heat up and burn the insulation.

Kenny, bite me but I did get two new battery's today and will try it out this weekend.

Doc, thanks im going to try this using a set of known good wires.

I have been chasing the same problem for a couple of seasons checked all grounds cleaned everything i could see finally sent all gauges to livorsi this winter they rebuilt several of them i hope this fixes if not i will try plug wires

Hey Trips I have had the same problem the last two seasons at or around 3500-4000 rpm's. Please let me know if you have corrected your problem with re-worked gauges.
Thanks,
JB

On my Pantera, my fuel sender and main ground block would get some light corrosion at the connections and would start acting eratic. It would peg and then go back and forth to normal. The ground for your tach could be intermixed with your ground to the fuel guages or it could be a short at you main ground block behind the dash. I never had any fuse failures or other electrical problems, just guages acting goofy. I don't think its shorting out with a positive lead, just not making a good connection at some point.

Check ALL of the connections on the back of ALL of the gauges. I had one that wiggled out of the crimp connector, and 1/2 of the dash went wacky as the boat would go over bumps.

It' not his gauges or the spark plug wires. The tachs were replaced with the good Livorsi ones. It did the same thing with the factory tachs. The engines had low hours on them and I switched over to 8.5 MM MSD wires and the problem still persisted. I talked to the guy at livorsi about this problem, he sent me some small circuit boards to install on the back of the tachs it made it worse. Jim can chime in but it only happens about 4,300 RPM'S and higher unless that has changed, and one tach is worse than the other. It has ground problems somewhere.
(I used to own this boat)

Its doing it from 2500 and up now, and yes one tach is worse than the other. Going to check grounds tonight and maybe even run new ground wire for the tachs.

Wouldn't a ground issue effect all the gauges?

I had some issues similar to this that turned out to be a dead diode on an alternator....

c spray how do you test or check for bad diode in alternator?

finally went out and my gauge problem is gone seems i had a couple of bad gauges if anyone does send them in to have them checked see if they can make all the old ones match any new ones they send you, I can tell which gauges are the new ones from the different color lights

Another good place to investigate is the main bullet connector on the harness. Sometimes you just need to pull it out and push it back in and it will improve. Not sure if this is a problem on the newer merc products but it was at one time.

THere is a problem with the Merc. smartcraft comp. THe tach just shuts off or randomly fluctuates. restarting the egnine will fix it but I wonder what Merc has to say about it. They know.. :) I talked to them.

Well I finally solved my issue it was the plug wires, both tachs are solid as a rock now. Checked the old wires per msd two of them ohmed out bad but never had a miss on either engine.

I just started to have this same problem on my port motor, at around 3500 rpm the port tach will flutter 500 rpm or so, both motors run strong fire good and clean burn, seems like the plug wires make the best remedy to correct this problem, mine is a 95 with 500 HP's, what wires would you recomend for best performance and least amount of interferance ? as well as best fit.