ECUMaster black to S14 SR20DET - ECU resets on cranking

Hi all,

I built a harness for my S14 to be able to run a ECUMaster Black.

Got my engine rebuilt and forged last year and due to work commitments i haven't been able to get near the car for a while, however I plan on getting back to it soon but remembered that when I was cranking the car to build oil pressure, the ECU would reset on cranking (i hear the bleep).

I remember seeing the voltage dropping to 9V but will stick a multimeter to measure min voltage on crank to get an accurate measurement.

I did try and wire a switch with hot 12V to the ecu so it wasn't being powered on by the IGN 12V and it still reset.

does anyone have any suggestions on what could be causing the voltage drop?

I

Furthermore, once this is resolved, I was advised to install an AEM trigger wheel. Can anyone help with timing, ign setting etc for that?

I have a detailed Excel with my wiring harness details and he ECUmaster file attached.

Thank you!

Gabriel N

It's probably a mixture of two things - where you are taking the power from, where it's grounded, and the gauge of the wiring.

Under cranking, it's not uncommon for the battery voltage to drop to around 10V, even less under heavy load, and if the ECU requires a minimum of, say, 9V, then it doesn't take much compromise to drop that 1V. It's sound practice to use a source at, or very close to, the battery and ensure there is a low resistance ground back to the battery. There are formulae for the wiring gauge for the ECU rated current, which can be useful, but i'd suggest going at least one size larger to minimise the voltage drops in the power and ground wiring, so it's less vulnerable to a low cranking voltage.

Hi Gord, thanks for the reply.

The battery ground is via a wiring specialties made battery ground cable attached to the metal battery box, which in turn is bolted to the chassis via three M8 bolts.

I will check the resistance to the battery soon and confirm. I can change that and bolt the negative straight to the chassis instead with a thicker gauge cable.

Positive cable goes:

Battery > cut off switch > post (where I draw 12V for the AMP from [disconnected at the moment]) > 150Amp fuse > cable runs through car to a firewall post > splits into 2 paths for starter motor and then fuse box power in the engine bay.

That ground doesn't sound ideal, so strapping it to the negative battery terminal will likely be a general improvement.

Is it possible the battery has been sitting during the build process and isn't in great shape? Oftentimes when they get bad enough, a battery may show static voltage that's decent, but they drop badly under load. Around here you can walk into almost any auto parts store and they'll load test a battery for free, but i don't know if that's available in your area.

Hi Mike,

I will re-do the wiring once it stops raining (the car is outside unfortunatelly) and put in a sturdy ground and check resistance.

Battery wise, it was new in October 2021 and i have kept it on a charger when it is not in the car but I will see if I can get it tested. The battery I have is this one:

https://www.halfords.com/motoring/batteries/car-batteries/yuasa-hsb005-silver-12v-car-battery-5-year-guarantee-548554.html

I have found the Black to be stable as low as 6-7 volts, at least not losing connection to a laptop via usb.

To me this sounds like a dead/dying battery compounded by a weak ground connection. I would also recommend grounding the negative terminal straight to the body with a paint free connection.

Testing resistance will probably look fine until the system is under load. Anything more then 2 ohms is a definite problem as it will get worse under the load of the starter.

You can try jumping the battery with another or a jump pack and see if that helps.

What triggering does the engine have on it now? your trigger settings don't look like a factory CAS setup

Gabriel,

Just checking in to see how you're doing. I hope you've been able to move past this point.