We now have a double effect causing the ECU ground to sit higher than the engine ground. Let’s assume the grounding to the ECU from the battery is also substandard, which means that as injector duty cycle increases, the voltage drop between the ECU and the battery also increases. As the engine speed increases, the alternator charge current increases and so the voltage drop between the engine and the battery increases also.
The coils are grounded to the engine, and the ECU is grounded instead to the battery. In this last example, the car has coil-on-plug ignition. This is fairly easy to spot in logs you can look for noise on inputs such as coolant temperature, throttle position etc, but it causes problems for obvious reasons. In the case of coolant temperature, it means that as injector duty cycle increases, the voltage seen by the ECU on the coolant temperature input reduces and the ECU believes the engine is at a higher temperture. The ECU ground will be sitting at a slightly higher voltage than the engine ground, so any sensors connected to the engine ground instead of to sensor ground on the ECU, will read a lower voltage. We know that as the injector duty cycle increases, the average ground current of the ECU will also increase, and therefore so will the voltage drop between the ECU and the engine. The sensor ground is externally grounded to the engine, as well as to the ECU. It’s actually a mistake made by Mazda in the factory NA6 MX5 / Miata loom they fixed it on the next model (the NA8).
This second example is one that I used to use when I interviewed support engineers to work for us, but I guess now I’ll have to think of another question to evaluate people. Exactly how much depends on the relative resistances between the ECU grounds and the ground strap if the ground strap is in good condition then not much but otherwise people have blown up tracks in the ECU by doing this. This in turn induces current in the ground wires going to the ECU or in other words, the ECU shares some of the starter motor current. During cranking, a lot of current flows through the ground strap between the engine and the battery, so there’s a voltage drop between the engine and the battery. You might ask why would anyone do that, but some people do because I find myself explaining to people why it’s bad. In this first example, the installer has grounded the ECU to the engine and also to the battery. Since we’re talking about the context of ECU grounding, we can look at the voltages from the ECU’s perspective and predict what can go wrong due to the voltage drops. Then remember that every wire has resistance, which means that you’re going to get a voltage drop across the wire, depending on the current flowing through it. To analyse a system for ground offsets, you first need to draw a diagram of the system. Ground offsets are often not very well understood, which is a missed opportunity because they are quite simple to visualize if you draw a diagram. The two main problems are ground offsets due to common impedance paths and magnetic field noise.
#ADAPTRONIC PIEZO INJECTOR HOW TO#
It is, however, complex, with several separate considerations, and when you see how they all interact you’ll see that there is an optimal solution which is the same for most cases.įirst of all I’m going to discuss the separate problems we’re trying to avoid, and then how to analyze them and optimize the ground layout for each of the problems. I’ve seen much “debate” about the best way to ground ECUs, so I thought I’d take the time to explain some of the theory, because none of it is that difficult to understand.
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