Squirly tach

[Bruce San]

I've got a E150TXCOS power head sitting on a J150TLCTB lower. This weekend my tach started acting funny. Up until this point it has seemed to work well. Now it sometimes reads ( and I'm guessing here ) 1000 rpms high. After a while it'll bounce back to normal then up high again. Do I just have a bad tach or could this be something else going bad in the ignition circuit?

 

[farginicehole]

Re: Squirly tach

I'm having the same troubles you've described on my E150STLCEM (an '89). This started last season and has gotten progressively worse, and sometimes the tach doesn't work at all now. I am interested to hear the replies you get to this question. I am having other intermittent ignition problems (randomly losing spark to 1 or more cylinders at any given time), so I am replacing parts to try to fix that first. I replaced all 6 ignition coils yesterday. Didn't figure that would fix it, but the old ones were cracked and I'm afraid they could be shorting to the block (if not now, soon!). I just ordered a new power pack today. Hopefully, if my current pack IS bad (i.e. this fixes my spark problem), a bad rectifier/regulator won't kill my new pack in short order. I'm guessing the guys here will tell you how to check your tach and your rectifier/regulator, as I understand that this is what supplies the signal to your tach. Good luck!

 

[JRuggiero]

Re: Squirly tach

check your rectifiers! all you do is disconnect the leads (two yellow and a red on my '71). take an ohm meter, and put red lead to the red wire, and the black lead to each of the two yellow wires. then do it the other way around with the black lead to the red wire... you should get no reading one way, and some reading the other way.

 

[Hooty]

Re: Squirly tach

You can check if it's the tach or not with a volt meter at the tachometer. It should have a minimum of 3.5vac between grd. & send at idle, and 5-7vac at 2000rpm.<br /><br />c/6<br />Hooty

 

[Bruce San]

Re: Squirly tach

Thanks guys! I'll get to it as soon as I have an afternoon with no thunder storms. Maybe today????<br />So Hooty, if the voltage is constant at the tach and the needle is still bouncing it's the tach. If the voltage is bouncing with the needle it's the rectifier. Right? next question: Is a bad rectifier going to burn up something else? Power pack?

 

[farginicehole]

Re: Squirly tach

Yeah, thanks JRuggiero and Hooty. A bad rectifier can kill the stator, can't it? I put my power pack order on hold until I can check the output of my stator. The resistance tests I did on it were a little low (20 or 30 ohms below the lower spec, according to my Clymer manual). If the voltage output is low (isn't it supposed to be greater than 200 peak volts?) too, could this be causing random cylinders to not spark? Sorry, I'm not trying to hijack this thread, but since I'm also having tach problems that keep getting worse, I'm wondering if I have a bad rectifier that is killing my stator too. I hear you about those t-storms, Bruce. One stray bolt of lightning can really throw your voltage readings off!!!