My tach recently decided to quit working properly. It will work sometimes, but it won't be accurate at all.
After reading Vince's post on diesel and gas tach signals, (very interesting read btw) I tested the W signal on my alt. And for some reason I got 16vAC at idle.
I am about to take my alternator apart to check connections and such but I don't really know whats going on. Is there something I should be looking out for specifically? I don't see why it would read double what it should be if the tach isn't even working. My alt is charging properly and working well otherwise.
Also, what does this little black box do? It doesn't make a connection from point A to point B.
A couple of thoughts:
- the black box is a noise suppressor... reduces the diode spikes a bit to quiet down the alternator whine some radios are susceptible to. Most modern radios have this feature built in already, so you usually don't see a noise suppressor on more modern cars.
- I haven't measured the output of the W-terminal enough to know if your 16V is normal or abnormal... it's the frequency of the waveform that the tach is looking for and so the actual voltage reading probably doesn't matter much.
- tach issues are often signs of an impending alternator issue... are you experiencing any other alternator problems? Is your battery charging OK ?? Have you measured your voltage (engine off, engine running) to confirm a healthy jump between the two ??
Yes. My alternator is charging very well. Just under 15V when running at idle and a bit above a healthy 12V when off.
I put new brushes and new bearings into the alt last summer. I have never had any kind of electrical issues before now.
Everything other then the tach is working well. I guess I might start looking for a tach or alternator soon.
I am wondering if there may be a grounding issue. However I don't where the alternator grounds to.
Grounds to the engine, which grounds to the battery. I would think 16 v should be fairly normal from a W terminal as it should be a little above the dc voltage.