Tach Issue
 

On my 84 With a stock 12A motorand when I first start it in the morning the RPM needle does not always move until the car has warmed up and sometimes only after it has been driven awhile. Can anyone offer some advice? Thanks

most likely your trailing ignitor is bad, your car probably runs rough when the tach isn't working right? I would try a new ignitor (well probably not brand new, but a good used one) and see what happens, that or check if you're getting spark on the trailing plugs.

If you don't know, the ignitor is located on the distributor, theres two of em, IIRC the trailing is the rear one, but don't hold me to that, its been awhile.

mine does the same thing when cold it doesn't work and when it starts to move it creeps up slow and sticks there for a bit too. If that's what your getting it's inside the tach the pivot points for the movement need to be cleaned. I'd suggest electronic cleaner followed by some light machine oil.

I have the same problem with my tach on my 84 GSL, slow to warm up but then works fine, just part of owning a 21 year old car, I guess. As numan indicates, this is a different problem than the trailing ignitor. I had a trailing ignitor problem, the tach was much more erratic, then gave out altogether. At this point, the fuel pump cut out and shut the car down. Incidently, for a quick fix, I discovered you can hot wire the fuel pump from the rear compartment light and drive the car, it runs pretty good without the trailing ignitor working. (But fix it if you want to beat mustangs).

Ray

re-route the tach wire from trailing to leading and see if that helps. I highly doubt that its the trailing igniter. Once its goes bad, its bad.

mine only does it when it gets in the 40's or lower.....the lower the temp the longer it takes to work. the coldest day sofar it never worked the whole 10 miles trip to get to work and it was about 38f that day. Little did Mazda know they invented a tach thermometer!!!

Mine works exactly the same way, here in NE Georgia that means it's been sticking in the morning these last few days, but it's supposed to warm up this weekend. Easy fix. Fortunately my GSL came with all the automatic repair options, so most things that stop working usually fix themselves, if you give them enough time.

Re routing the wire will cause your tach to double in given rpm because the trailing ignitor fires twice per combustion event.

Thats new to me. In my RX-3, Im running an autometer 10K tach connected to a MSD 6A and stock tach to the trailing. No difference.

where did you get that datum from? that's new to me too.

It's not news to me. Marek just doesn't fully understand all the ins and outs. :D

Well Jeff, care to elaborate and enlighten an ignorant fellow rotorhead? :)

Also Marek, how would rerouting the tach cable from trailing to leading would double the tach speed, if the trailing ignitor fires twice per combustion event? in that case I'd think the rpm would be cut by half.

Sure. The reluctor has four teeth. Each pickup sees two teeth per revolution because the dizzy shaft spins half eccentric speed. Two teeth per rev equals two ignition events per rev. Leading and trailing both have two ignition events per rev. This means it does not matter whether the tach signal wire is hooked to the leading coil or the trailing coil as either one outputs two pulses per rev; the same as a typical 4 cylinder (set an aftermarket tach to 4 cyl mode for use on a rotary).

cdrad51, you actually do understand what's going on. :)

Thanks for the info. Did what Numan said and hopefully it will work in the morning. We had warmer temps to day in Central LA. with a little sunshine. Hopefully the weather will be great for Mardi Gras this weekend. Just imagine if Mardi Gras and the Superbowl in 2001 was going on at the same time. Thanks again for info

an easy way to test it is after fixing the tach put it in the freezer for an hour or 2 and move the needle by hand and see if it sticks.

Well now I do, thanks for the explanation. :bigthumb: