Ecumaster EMU Classic - erratic charging voltage drop (graph included)

Hi, all!

First time posting here. Also it's my very first time installing a standalone ECU so I'm learning as I go.

I'm aware that voltage drop issue has been previously discussed on this forum but I didn't seem to find a topic describing my problem. So here goes...

First of all, specs:

Nissan 200SX S13 CA18DET (Euro spec)

Ecumaster EMU Classic ECU (CA18DET stock modified wiring loom)

NGK U5014 ignition coils (custom coil side wiring loom, stock ignitor removed)

DW 550cc injectors (low impedance)

Stock alternator (fairly fresh, about 20K kilometers on it)

Walbro 190 LPH fuel pump (Nissan stock wiring)

I have a strange problem with charging voltage. When ignition switched on, Ecumaster software displays voltage about 12.45V (about 12.65V measured at the battery terminals). When engine is running, the maximum voltage is about 13.6V and dips rapidly below 12.5V, slight engine stutter occurs. Voltage on battery terminals while engine was running measured steady 14.2V, no fluctuations, so I assume the alternator voltage regulator is functioning as it should. I also tested alternator charging voltage with a battery/starting/charging system testing device and it passed.

I suspect it has something to do with grounds but to my knowledge everything seems to check out.

EMU ECU ground pin (B17) = Nissan loom wire no. 60

Sensor ground pin (B18) = Nissan loom wire. 26 and 30 spliced together (also Bosch knock sensor ground and wire shielding)

Power ground pin (G17) = Nissan loom wire no. 10

Other 2 power grounds (G24, B24) are different Nissan wire numbers but they all join with no. 10 further down the loom.

I attached log graph screenshots and emulog file to this post.

All ideas and suggestions would be very much appreciated!

This is due to the fact that the 12V+ Key On wire that goes to the ECU is also feeding the fuel pump. I usually put a dedicated relay with a fuse that comes from the battery. If you don't do that, you'll have wierd sensor reading as well and your fueling could vary mostly at idle because the engine is compensating for the dead time (but the voltage at the injector will be solid 14V).

A quick way to check that is to run the fuel pump with the engine not running. You'll probably see the same spike in the log.

EDIT : Also, to prevent problems for future upgrades, I advise you to upgrade your fuel pump wiring.

You were right about the ignition switch feeding the fuel pump. Thank you for the tip, Frank!

I rewired fuel pump relay contact circuit directly from the battery (fused of course) and the charging voltage was hovering around 14V (+/- 0.2V) most of the time judging by the software voltage display gauge, however the log still shows some worrying dips and spikes: lowest about 7V and highest 20V. These extreme transients did occur only couple of times though but dips below 13.5V were still common. Also the engine misfire was even more prominent now. Coil dwell times are set from Ecumaster preset.

Any other ideas?

You will need to go on the hunt for a bad switch, broken wire, corrosion on a terminal (either ground or power going to the ECU). These are hard to find, but at least you can log to know if you've fixed it. Usually wiggling wires while watching the value live will allow you to find the problem. It can also be a cracked solder connection in the ECU itself.

Do you only see the voltage problem when the engine is running?

A 20V spike is potentially a concern as some electronics may have issues with that.

Possible causes are a bad voltage regulator for the alternator - had this happen on one car, blowing 5 of the 6 headlight filaments on an unlit road... - or a highly inductive load somewhere, such as a cooling fan switching off, driving the spike. If the alternator uses a referenced voltage, don't forget to check that wiring too, as if that OCs'it may register that as a low voltage and increase the output to try and compensate.

As David said, because of the huge range in voltages reported, a very careful check of the wiring and connections would be a wise move. Do not forget all the earths/grounds, as well - for example, some alternators use insulated mountings and require a separate ground, and make sure it's of a high enough gauge as I've hade one get hot enough to melt the insulation on it.

@David Ferguson - Yes, voltage problem is there only when engine is running. I ran the fuel pump when engine was off and did not see any anomalies in the graph.

@Gord - I will replace the voltage regulator next and see if that makes any difference. Luckily in this context I do not have an electric cooling fan, so that can be ruled out. Igniton coils are probably the most power hungry engine related parts after the fuel pump. Wiring check certainly wouldn't hurt.

Hey Keijo!

Maybe I didn't explain it good enough on my last post. For the ECU Master power, did you connect the ignition 12v+ that comes from the pin 45 of the OEM wiring directly (Black / Red wire)? If yes, that's probably your problem. There are other circuit that are powered from this wire.

My fix for this is using this Black / Red wire as a trigger (pin 86) for an additional relay, and use a dedicated 12v+ source (like the battery via a fuse) to power the ECU from this additional relay.

I have attached some print screen of before and after the fix.

Maybe it's more clear like that.

Hi Frank!

I think I get the idea now. My ECU is still powered by pin 45 red/black wire, last time I just wired a deticated wire from battery to fuel pump feed circuit (which helped a little bit) but I overlooked the ECU power supply. As it happens, Nissan loom has live wire (red, pin 58). Maybe I could use that one to power the ECU with separate relay (fused)?

I’m not super familiar with the CA18 wiring, I just checked the wiring diagram and this wire going to pin 58 seems to be powering the injectors. You can try it, but to be honest, I would just connect it to the best power source possible as the Classic uses only one 12V feed, so in my opinion it better be the best one possible.

Good news!

Frank was absolutely correct about this one. ECU needed an alternative power source. I powered the ECU from Nissan pin 58 with relay and that did the trick, voltage is stable now.

Thank you Frank, I owe you a cold beverage! Also thanks to David and Gord who took the time to chip in ideas.

Case closed.

Well, I wouldn't say no to a Põhjala... hahaha!

No worries, I'm glad I could help!

Why did you need a relay here and how did you wire the relay, I am assuming off PIN 45?

NVM it's because you're using a classic and not the black