aftermarket tacho issues

[bad_religion_au]

ok, i found the wire that feeds the tacho on my bro's 4a corolla motor. now the tach does move when the engine is running, but behave irrattically,

for instance, it'l spike in RPM after you back off, it'll idle around 1500rpm but peak out at 3000rpm, (even thought idle is 800, and peak is about 6000)

any idea on what is goin on... the toyota manual for it says "some tacho's will be unsuitable for this type of ignition system" (high energy ignition apparently)

how do i find out what's compatible? the manual doesn't help me, nor does the tach instructions...

[sudso]

Is the tacho for a 4 cyl and for HEI?
I bought a cheapy once for my HK and it had a 3 setting switch on the back, one for 4,6 and 8 cylinder.
Worked right but when I had the car dynoed the mechanic discovered that the tacho was drawing too much power from the HEI ignition coil!
It read correctly but farked the module on the dizzy.
A 2nd hand module and a disconnected tacho upped the power to 130kw at the wheels along with a bit of a tune.

I never knew a tacho could mess things up like that!

[bad_religion_au]

yeah it's for 4 cyl.

as for HEI, well i dunno... the box doesn't say, the instructions say "for electronic ignition, consult your car's handbook for best hookup"... car book says "consult tachometer instructions"

hmmm

is there a circuit or adapter or somethin for it? why does HEI mess with tachos?

[nicbeer]

Is it a carb or efi 4a?

I had a cheap $20 on my rolla running fine. 4a with carb.

cheers

[bad_religion_au]

Is it a carb or efi 4a?

I had a cheap $20 on my rolla running fine. 4a with carb.

cheers

4a with carb... apparently a "HEI" ignition system according to the service manual, if that matters.