problem with defi rpm gauge

[fax0815]

Hi,
I have a little problem with my defi rpm gauge.
It´s picking the signal from the cable going to the genuine tacho in the dash cluster (Zenki AE86). Unfortunately its not very accurate, on low rpm it displays 250less above 6000rpm the offset amounts up to 1000 rpm.

I do trust the OEM gauge, since rev limiter and cold start rpm are displayed as supposed.

Any ideas whats wrong?
Should I much rather wire it to the rpm signal cable for the ecu?

Thanks.

[Project D]

the original Tach get the information from the coil, wich is not the best for a defi gauge.

try on the "Ne" pin of the ECU (Ne = engine speed sponsor = rpm)

if you have a MAP:


if you have a MAF:

[fax0815]

Thanks for confirming my mistake, will change it soon!

[fax0815]

Ok, rewired it to engine RPM signal going to my ECU (Ne).
Now its not working at all. If I turn i it on it goes directly to the top of the defi tacho!!!

Heeeelp needed...

[Project D]

To make it work properly you need a proper square wave like defined in the manual:
http://www.defi-shop.com/installation/manual/

The Coil signal is a "spike" type, so you definitly can't use it properly...

The Ne signal is supposed to be a square wave who oscilate between 0 and 12v (if you have an oscilloscope to confirm...),
so with the blue wire (not the light blue on the old "BF" or "Racer" serie) it should work.
If not, then I don't know...

You can also try on the IGt signal, it's a 0/5v square wave (so still the blue wire of your gauge)
->Not really recommended because it's the signal who actually make the coil working. It will not dammage anything BUT it can result in bad firing for your engine.

[fax0815]

Hi,
I´ve been thinking about what´s going on there...

In my opinion the NE signal is wrong! The tacho worked inaccurate (but it worked) conected to the neg. side of the coil. This gives a peak signal for every spark, the contolunit (set to 4 cylinder) calculates the rpm based on that.
Now its conected to the rpm singnal from the dizzy, providing a square signal, but way to much peaks (did not count the teeth on the triggerwheel) compared to what the signal from the coil.
To much peaks explain why the gauge goes straight to the top as soon as the engine starts.
Wrong signal...

My idea is to use the signal from the 4 tooth trigger wheel that the dizzy also provides.
Does anybody know to wich pin it is on the ecu? Is that the IGT signal you´re talking about?

Hopefully it works

[Project D]

The dizzy signal (toothed wheel + vr sensor) don't go straight to the ECU, it go to the igniter (small box over the coil) and the igniter convert this signal to the Ne Signal for the ECU...
But maybe you're right about the frequency (too high ?)

Instead, the IGT signat goes from the ECU to the igniter,
it "drive" the coil so the signal must be good
(2 spark / rev, like any 4 cylinders engine)

here is how it work:

[Bean]

if you don't/can't use the NE signal the IGF would be next to try... this is the confirmation signal from the igniter to the ECU.

have a good read here: http://www.autoshop101.com/forms/h23.pdf
(diagram on page 6 is the OEM AE86 setup)
and also have a good read of the Defi manual to check what it wants to see.

PS: what model tach do you have partnumber - iirc they have usually two different input wires depending on the signal you supply.

[irishtwincam]

Ne is 24 tooth
G1 is 4 tooth (2 signals /rpm so #1 tdc reference)

unless youve MAF in which case its 4tooth and 1 tooth.


You need to run the defi from Coil-, maybe with some suppression and a diode. Id image the defi is losing some energy due to two tachs running off the same wire?

[fax0815]

Hello,

tried everything you suggested, no signal going or comming from the ecu gives a decent reading!
Wired it directly to the coil, still the best signal, but still with mega offset.

I´m not an electric engineer, how do I convert the signal from the coil to something smooth and square?