Distributor Pickup Coil Question

PAguy
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Posts: 20
Joined: Thu Jul 02, 2015 12:25 pm
Location: Western PA

Distributor Pickup Coil Question

Postby PAguy » Fri Aug 25, 2017 6:48 pm

Is there a crank position sensor for the 4AGE, or does the pickup coil in the distributor do that instead?
Trying to diagnose a sudden tach randomly flopping/pegging while engine is struggling to keep running.
Western PA
Long string of old Toyota's over the decades.
Currently daily an '84 SR5 hatch, an '85 GT-S coupe and a 91 FJ80.
Daughter #3 has an '86 MR2.

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jondee86
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Location: Wellington, New Zealand

Re: Distributor Pickup Coil Question

Postby jondee86 » Sat Aug 26, 2017 12:31 am

On the AE86 the tach signal is output by the igniter which takes the voltage spike
generated by the coil negative and passes it on :) There are two trigger wheels
in the base of the distributor. The one with more teeth generates the rpm input to
the ECU and the one with less teeth generates the crank position signal. Neither of
those trigger wheels has any direct connection to what the tach is doing.

To make it clear... the trigger wheels rell the ECU what the engine is doing, and
the ECU uses that information to tell the igniter when to fire the coil. A signal to the
tach happens every time the coil fires. So if the engine is struggling, the speed will
be erratic, the spark timing will be erratic and the signal to the tach will be erratic.

Cheers... jondee86
Give a person a fish, they eat for a day. Suggest they search before posting, and they learn a skill for a lifetime.

PAguy
Club4AG Regular
Posts: 20
Joined: Thu Jul 02, 2015 12:25 pm
Location: Western PA

Re: Distributor Pickup Coil Question

Postby PAguy » Sat Aug 26, 2017 4:08 am

Clear.
Big thanks Jondee!
Western PA
Long string of old Toyota's over the decades.
Currently daily an '84 SR5 hatch, an '85 GT-S coupe and a 91 FJ80.
Daughter #3 has an '86 MR2.

PAguy
Club4AG Regular
Posts: 20
Joined: Thu Jul 02, 2015 12:25 pm
Location: Western PA

Re: Distributor Pickup Coil Question

Postby PAguy » Sat Aug 26, 2017 4:11 am

I've always said the igniter is electronic points, so that sounds pretty close.
But if the coil lies to the igniter, the tach WILL freak. And the engine won't be too happy either.
Over the past 5 years, 3 of my old Toyota's have had the pickup coil or igniter go bad. In every case, the tach floppiness was the smoking gun.
Western PA
Long string of old Toyota's over the decades.
Currently daily an '84 SR5 hatch, an '85 GT-S coupe and a 91 FJ80.
Daughter #3 has an '86 MR2.

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