eichhoma

iTrader: (1)

Well, we did more testing this only to leave me even more confused. We found that disconnecting my alternators completely from the system made my tachs work just fine. So we swapped them out with the alternators from my buddies Fountain (same exact alternator/part #) and they still fluttered and fell back towards zero at 3800 RPM!! We also ran a known good tach directly to the coil and it worked fine.
Then we narrowed in on the harness to the alt's and the wiring to the tachs in the dash... ran known good grounds, signal, and power directly to the tachs with no improvement.

I spoke to Livorsi and they suggested I try a couple new tachs, ones with metal cases... mine are plastic. They seem to think it is interference/ radio frequency interference stuff that maybe the better cases might prevent. I think its a reach but bought a couple to try out. They should be here tomorrow. They are working with me so I cant complain. Said they would take them back without the resotckinig fee if they still dont work. The bottom line is the tachs were fine before the engine rebuilds, and the only thing different is the blocks (went from 454's to 502's)... I cant understand what could be different now that someohow some freak signal is being sent out to interfere with the tachs??? The alternators have me very curious.... but the wires going to them are all good.

Any other suggestions? Much appreicated fellas.

cloudmaster_321

Could try this............
http://www.lonestaraviation.com/prod...nator%20Filter

Wobble

That is a good idea. also is there any chance that you went from a resister type spark plug to a non resister? I am sure that you are not running the same plugs if you went from NA to blown

http://www.ngk.com/sparkplug411.asp?...esistor&mfid=1

Boat Tech

[IMO] You need to seperate the engine from the helm wires, If you can find a new cannon 10 pin wire harness plug from a dealer that might have a good old one laying around in the back of the shop area somplace, You could plug it in and and make up a small seperet dash on a borad of some kind and install a IGN key switch and a tack and what ever eles gauge you want to hook up to it and wire it up and go run the boat and see if it still does it. This way you will know if you are trying to fix the engine, or the wires to the helm or the helm gauges them self. It just makes it easer to find what you need to look at to start fixing. I do the same thing some times when I am trying to find a fuel problem, Seperate the boat from the engine, It so much easyr, Hope this helps if you want to do it good luck.

Boat Tech

X 2 on the plugs, By the way what plugs are you running in the engine right now? [IMO] There just seems to be less problems with NGK spark plugs.

tbanzer

Did you check the 5-7 plug wires in the loom? I had the same problem and that helped my situation. I ran the tach off a seperate battery and ran a seperate wire directly to the tach from the coil and it acted the same. Went up to about 4k and all was fine, as I increased rpms it would hold there then fall to zero. Went threw a couple of new tachs with the same results. For the rest of the season I just lived with it. The next season I was looking over things and I noticed that 5 and 7 were running next to each other , seperated them and all was good. On the 90s GM trucks they would set a code in the ECU for having the wires ran together.

eichhoma

iTrader: (1)

I did check the wire looms and ensured that 5 and 7 were not running right next to each other. I am also curious about the spark plugs myself. I know the builder put new plugs in but I am not sure what type they are, I will check tomorrow when I am down and into it again. The motors were already blown before so uit wasnt a conversion from NA to blown, but that still doesnt mean non resistor type plugs are in there.

I haven't gone as far intot eh wiring as boat teck suggested but it looks like that needs to be the next logical troubleshooting step, thank you for the feedback.

Any more suggestions? I really appreciate it guys.

nordic95

I had the same problem as you last year. Pulled motors to freshen and then re installed and tachs were bouncing after 3500. I called Livorsi and they sent me two filters to install on the back of my tachs.That didnt work so they sent me two new style tach with filter built in and they worked perfect.They are a couple of hundred rpms off from one to another but at least I can read them now up to 5700...

Anthony

eichhoma

iTrader: (1)

Thanks Anthony.... I have a couple on the way from Livorsi and am going to try them out this weekend.... SInce you were in the same situation, I still cant help but wonder what is different... somethign obviously changed or was connected differently than before the motors were pulled.... Thanks! I will let you know the results with the new tachs. Mark

johnnyboatman

iTrader: (5)

Hey Was That The Correct Cable End.