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Electrical problems - voltage drop

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Hello everyone,

Got an Audi urs6 (2.2 AAN), switched from stock ECU to standalone EMU Black EMU.

Basically, I still can't figure out the voltage drop I get while turning on anything electrical in the car (headlights or heater for example).

If I turn on the low beam or high beam, my lambda goes a bit rich, and my tacho won't go above 5000 rpm and working erratically although in EMU software I can see it going 7000+ rpm just fine. The high beam would make it run even richer.

EMU Black would record a small voltage drop 0.3-0.5 if I turn anything on, but I'm pretty sure it's different to what it actually is, I will take a measurement at the injectors and update the post.

I have used the stock wiring, just made a PnP adapter for the EMU.

The measures I've taken so far:

I have triple checked all the grounds on the car

Removed the dashboard, fully disassembled and made sure I have no issues with it

I checked the voltage drop on the alternator and on the battery, again it's just fine (0.2-0.5v)

The injectors are calibrated properly so even if there's a voltage drop they should compensate just fine.

I did not have any issues like this on stock Motronic ECU.

Any ideas?

What relays I could check, or maybe you could point me in the right direction?

That usually leads me to suspect the field supply to the alternator. Either its erratically exciting itself or its just jacked.

Hi Vlad,

Where exactly are you checking voltage drops (as in, where are the positive and negative leads of the voltmeter?). A 0.5V drop is significant---that is half of a volt!

Also, remember that a voltage drop can be on the power OR ground side---so when you say that you "triple checked" grounds, was a voltage drop test performed on the ground side?

I'd recommend starting fresh and checking voltage drops at each point on both the power and ground sides: alternator B+ terminal to junction point, fuse block, battery B+, and to the ECU/harness itself. Same for the ground side. There shouldn't be much more than a 0.2V drop at any point with loads on (headlights, blower fan, etc).

You mention that you have your injector compensation table set up, which in theory means that injector pulse widths should be OK, but your symptoms of the tachometer and WBO2 readings being inaccurate with loads switched on point to a voltage drop situation somewhere in the system.

Of course if all of the above is OK, then either the alternator or voltage regulator/field circuit is faulty.

Thanks everyone for trying to help.

First things first, I just wanted to check if indeed there's no link in my wiring between Power Ground and Sensor ground.

Basically I have an oil pressure sensor that i've installed myself (5v , analog input, sensor gnd), so I used it to check if there's a link between sensor gnd and power gnd.

I tested for continuity between sensor gnd and engine block, and there's indeed a connection between them, with nearly 0 Ohm resistance.

So I started to check all the grounds again, spent like an hour to make sure that I did not mess up with my PnP adaptor and can confirm that there's no issues I can see with the wiring. Sensor gnds and Power gnds are separated.

Okay, next there's a funny thing, I became curious maybe it's the ECU that makes fun of me, so I checked for continuity the pins on the ECU between Sensor gnd's and Power gnd and finally Sensor gnd and ECU Gnd.

No link between Sensor Gnd and Power gnd , however there IS continuity between ECU GND and Sensor GND (I am not 100% sure if this is how it is supposed to be).

Although I followed the instructions on the Ecumaster website, where there is clear instruction on what and where to connect specifically for my engine, I can assume that there should not be any continuity between ECU GND (which is connected to the chassis or engine) and Sensor GND.

After unplugging the ECU I did the continuity test again between a sensor GND and Engine block, and there is NOT any continuity.

I am super confused now and really want to clarify if the grounds are right first before diving deep into the voltage drop.

Thanks everyone.

4:37am here, so might (will!) need some serious editing, but here goes.

With electronics there can be a different ' grounds' - some circuits require a common ground, and electrical source, as even minor voltage variations can cause problems - some will play up with variations in milli-volts' range, some are sensitive to even lower voltages.

The reason some are concerned with how you're grounding the various parts of the system is that with circuits EVERY part of it is slightly different from every other part, in isolation, this isn't really a problem. But a vehicle's chassis is a network of ground points, it is also part of the various electronic circuits that the ECU is working with, and the potential voltage at different points can be affected as different currents are grounded at different points, often through common grounds used by other components.It' s the same principle as the power supply, just the other side.

Hmm, that may be a bit confusing.

OK, just as powering some circuits can affect other circuits because the change in current draw affects the voltage - think that slight flicker you sometimes see in the dash' lights when the indicators operate, that slight voltage change may be mostly on the power side, but there will be part of that variation on the ground as well, and if the ECU is expecting it to be sourced.

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