mwatson184

Tach bounces at the following times.

1. When in neutral, reving the engine.
2. In 1st-3rd gear, while accelerating.

Does not bounce at these times

1. At a stop, idling
2. At a stop, reving engine with shifter in 4th gear/5th gear position.
3. While decelerating in any gear
4. While accelerating in 4th/5th gear.

I am curious to find out why the tach only bounces in 1st through 3rd and only while the gas pedal is pressed. Any time the shifter is in the 4th/5th position tach holds steady and strong. Anybody have any ideas? Thanks guys.

-Marques

wwilliam54

what year

mwatson184

sorry, forgot about that part, it's an 80.

This is my first fb, (I have a couple fc's) so now I have to learn all the little problems about these also.

wwilliam54

hehe its an SA

I have no Idea, but maybe someone will know

mwatson184

bump. am I going to have to figure this one out myself? I hate doing that

-Marqueds

specRX7_22

check to make sure the trailing ignitor is tight, it could be tiny bit loose. also, it could happen if the motor is surging from something voltage related (alternator, etc).

the fact that it does it in some gears and not others doesnt make sense to me.

mwatson184

the tach will be fine and steady in 1st through 3rd on decel. As soon as my foot touches the pedal the tach starts bouncing again.

Upon further inspection today I found that it will read the engine RPM up until 1400 rpm in neutral, anything past that it will just start bouncing again.

I thought that this would be one of those common problems that someone could just fire a quick answer for, oh well, i'll get it figured out.

X605

yeah check the coil wires. i had my SE do this once, one of the wires was lose.
job

RotorMotorDriver

iTrader: (1)

Dont the SAs run the tach off the leading ignitor because the trailing only operates part of the time?

~T.J.

Wankelguy

Yes, I believe you're right. The trailing plugs would be cut when the thermal reactor wasn't getting enough unburnt gas to continue the combustion in the thermal reactor. Bitchin' huh? If your motor was running too clean, the little weasel would dirty itself up. Nice!
There is another possibility, too. The '80 models had the ignitors mounted remotely in a little box on the fenderwell. The problem with this arrangement is that the triggering pulse to the amplifier (ignitor) from the distributor is so weak that due to the extra wire length involved and the close proximity of the two leads, cross-triggering can occur and that might cause the tach problem described, although for the life of me I can't understand why it would be gear dependant. You can disable the trailing-cut "feature" by jumpering the +12V terminals on the coils, but outside of replacing the '80 electronic distributor with an '81-above unit, or possibly rewiring the sending wires with some shielded wire, there's not a lot that can be done about the cross-triggering if indeed that is what's happening.