Mechanic says my tachometer is bad, happening alot with E-TECs. True?

[coores14]

Some of you may have seen my other ongoing thread about trying to get my RPM's up a bit on my 150 E-TEC. The dealer has my engine mounted as low as it can go and i'm spinning a 15x15 prop to barely 5000rpm. He is now claiming that they stuck it on the computer and they determined that it is my tachometer that is reading about 300-400 too low. He says that he's seen a bunch of this with the E-TECs, whereas I haven't heard about it at all on any of these forums. Even if the tach was reading correctly, it still doesn't explain why i'm only topping out at 39.8mph. I should be getting more speed on a 20'CC. I've been asking for him to raise the engine a hole or two and he's fought me the whole way. The cavitation plate right now is even with the bottom of the boat and I can't see it above the water when on plane. The dealer says that it's "set up right". I think that I finally convinced him to do it. But still, my main issue is with this tachometer thing. Anyone have any input? Thanks!

[jiggin]

I went from an "02 Ficht to this new E-Tec using the same tach. It's as dependable now as it was before. Maybe your service dude needs to just readjust the tach and see then if it reads correctly. As far as the mounting, same rules I think would apply for you as the rest, raise the motor and watch the water pressure and the RPMs in relation to the speed. Depending on your weight, you may not get more than mid 40s at best.

[RUSTY63]

I don't see problems with E-Tec's but I have found Tach's that read a couple hundred RPM's low.

I think I would get him to raise the motor.

[rudetech1]

The most accurate way to check the EMM out put is with a Hz meter, this will give the dead on reading. The tachs with the E-tecs are as reliable as they always have been, there is some loss of accuracy from digital to analog, usually about 50 rpm. Sometimes a bit more or less due to the tach, not the engine. Some tachs do NOT fall all the way to -0- when the key is turned on, some even start at 100-200.If this happens, tell your dealer to get you a new guage, it should drop to -0- when the key is turned on. The digital guages will be more accurate, they read what the CPS is reading, there is not much room for error here!!!

[pioneer197]

Dealer says the tach on my boat reads about 100 RPM low at WOT as compared to the laptop reading. E-TEC 150

[OkieBoatMech]

Been having problems with the tach's on a Ranger/ETEC set-up at our shop. They are giving false overheat warnings, lagging shown RPM vs Actual rpm., no system check boot-up, etc.

[luckystrike]

coores14, Tachs have been reading low but it has nothing to do with E-Tec. As far as lifting your motor a hole or two I would try that and maybe you can swing a larger pitch prop. You are getting as good as you can expect out of your 15x15 prop with your gear ratio and at 5000 rpms you should see 38.35 with no slip and at 5300 and 5% slip 38.62 mph so 39.8 is pretty good.

[coores14]

luckystrike, thanks for that solid technical info. makes me feel a little better.
an update to my situation: the tachometer was replaced and the engine was raised one hole. I took it out this past Sunday, but getting solid numbers was difficult. I had 4 people in the boat, a full tank, and the wind was blowing a solid 20knots+. I tried WOT and hit 5300-5400 with barely a change in speed from before. I'm guessing it'll do better when I run it by myself in calm winds.
My question is this, should I consider going up one more hole to bring the RPM higher and then moving to a 17 prop to bring them back to where they should be? Would there be an advantage to running a 17 or, for that matter, any different prop than my 15x15 aluminum one? Every other boat in my size range with a 150 is turning a 17 or 19, that's why I'm still curious. Different pitch, cupped, stainless, etc...?