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Chapter 5 DIY Electronic Modification Using a multimeter and finding the right wires. B EFORE YOU START delving into your car’s wiring harnesses intent on gaining a better performance outcome, there are some things you should know – such as how to use a multimeter (and what to look for when buying one) and how to find the right wires and then tap into them. Selecting A Multimeter The most important tool that you will use when making electronic modifications to a car is a multimeter. A multimeter is a test tool which can measure a variety of different electrical factors – voltage (volts), current (amps) and resistance (ohms) are the basics. However, while you might be able to pick up a basic volts-ohms30 PERFORMANCE ELECTRONICS FOR CARS amps meter for under $20, in the long run it pays to dig deeper to get a meter with these extra functions: •  Frequency (Hz) •  Duty cycle (%) •  Temperature (°C) •  Continuity (on/off buzzer) Multimeters are available in either digital or analog forms. While the upmarket meters (with duty cycle and temperature facilities) are all digital, the humble analog meter does have some application when measuring a variable signal which is changing very rapidly. This is because the digital meters sample at a relatively slow rate (eg, three times a second), while analog meters are constantly measuring. If all you’re looking for is a swing of a needle – and not the actual value of the measurement – then an analog meter has got some pluses. Note that all meters – analog and digital – which are being used with engine management systems must have a very high input impedance, otherwise the circuit being measured may be loaded-down by the current drawn by the meter itself. In almost all applications, a digital meter will work fine – and it’s also easier to read and more accurate. Multimeters are available in autoranging or manual-range types. An auto-ranging meter has much fewer selection positions on its main knob – just Amps, Volts, Ohms and Temperature, for example. When the probes of the meter are connected to whatever is being measured, the meter will automatically select the right range to show the measurement. By contrast, meters with manual selection must be set to the right range first. On a manual meter, the “Volts” settings might include 200mV, 2V, 20V, 200V and 500V. When measuring battery voltage in a car, the correct range setting would be “20V”, with anything up to 20V then able to be measured. While an auto-ranging meter looks siliconchip.com.au Fig.1: it is very important to take note of whether the wire location in the harness is being shown from the Electronic Control Unit (ECU) side or the wiring harness (W/H) side of the plug. As can be seen here, the apparent position of the wire changes quite a lot! [Lexus] much simpler to use – just set the knob to “Volts” and the meter does the rest – the meter can be much slower to read the measured value, because it needs to first work out what range to operate in. If the number dances around for a long time before settling on the right one, it can be a pain for quick measurements – and very difficult if the factor being measured is changing at the same time as well! For this reason, some auto-ranging meters also allow you the option of fixing the range, to speed up readings. Using A Multimeter So much for the preliminaries – but how do you go about measuring volts, amps, ohms and all the rest? When measuring volts, the meter should be connected in parallel with (or across) the voltage source. Most This view shows just how many connections there are inside an ECU. When tapping into – or intercepting – signals, finding the right wires is critical. commonly in a car, you’re trying to find a 12V source or you want to measure the voltage output from a sensor. In either of these cases, the meter would be set to its 20V (or 40V or auto-ranging DCV scale, depending on the meter) and the meter probes connected to the wiring. If the polarity is wrong (ie, you’ve connected the negative multimeter probe to the positive supply line), then no damage will be done – the meter will simply show negative volts instead of positive volts. Note that when measuring voltage, the circuit is left Fig.2: this diagram shows that when the ignition is switched on, a voltage (specified in the text of the workshop manual) should be able to be read between the two nominated terminals. Note that the plugs are being back-probed from the wiring harness side. [Lexus] siliconchip.com.au intact – the meter is simply connected across the device to be measured (ie, in parallel). Conversely, to measure current (amps), the circuit must be broken and the meter connected in series across the break. This ensures that all the current flows through the meter. Note that if you’re measuring currents greater than a few hundred milliamps (a milliamp is .001A), the meter’s positive probe must often be plugged into a different socket. This socket will usually be labelled “10A DC”. Failure to do this could blow Fig.3: this sensor has been unplugged from the loom so that a resistance measurement can be made between two of its terminals. Resistance measurements should always be made with the device out of circuit. [Lexus] PERFORMANCE ELECTRONICS FOR CARS 31 This photo shows how a speed signal has been obtained by tapping into a connection near the ECU – it’s the added thick red wire. Stripping some insulation from the ECU wire and soldering the new wire to it gives a trouble-free (but still reversible) electrical and mechanical connection. Note the yellow cable on the right – it’s an airbag lead. In cars equipped with airbags, you should be very careful about delving into the wiring harness without first consulting a workshop manual! an internal fuse or even damage the meter. Resistance measurements require that the device be isolated from its normal circuit, otherwise the reading will be inaccurate. In the case of a sensor (eg, throttle position), this means that the device must be unplugged. When a multimeter is set to its resistance function, it passes a small current through the device being measured. This won’t damage the device but it does mean that the multimeter battery is being drained during measurements. For this reason, don’t measure resistances for a long period. Before making measurements, always check that the multimeter indicates zero resistance when its leads are touched together; if it doesn’t, what chance does it have of measuring a real resistance accurately? Signal interceptors allow extensive electronic mods to be made without swapping to a new ECU. They work by altering the existing ECU’s input and output signals, to match the new engine requirements. To do this, you must be able to locate the right wires to connect the interceptor circuit and then carefully tune the modification. 32 PERFORMANCE ELECTRONICS FOR CARS Duty cycle is be measured by connecting the meter in parallel with the device. Fuel injectors and other pulsed actuators should be measured under real operating conditions and the best way of doing this is on the road, with the multimeter located inside the cabin. Temperature is usually measured using a bead or probe-type thermocouple. The bead unit has very little mass and so reacts quickly to temperature changes – but it’s fragile and hard to handle. By contrast, the probe type has a slower reaction time but is easier to handle and more robust. Using the thermocouple feature of a multimeter is as easy as selecting that function and plugging in the probe. Some meters also have an internal sensor which measures the ambient temperature and this can be useful when comparing test results from different days. The continuity function causes an internal buzzer to sound when the meter’s probes are connected together. If the probes are connected to different points in the wiring and the buzzer sounds, it indicates that there is a complete circuit between them. This function is very useful for checking that you have an earth or that there are no breaks in a wire. If you want more details on using a multimeter, refer to the instructions in Chapter 7. Working On Wiring Looms One of the very first steps when modifying a car’s electronic systems is to find the right wires. That’s harder than it sounds – some cars have ECUs with hundreds of conductors disappearing into plugs, while in other cars even finding the ECU itself can be a major drama. A fundamentally important step is to have an accurate and clear guide to the wiring and in nearly all cases, this means having a good workshop manual. All car manufacturers produce manuals for the guidance of their factory mechanics – and with no ifs or buts, these are the best manuals to have. Some manuals not only show repair and diagnostic procedures but also give very good explanations of how systems actually work. Suzuki, Toyota, Mazda, Holden and Ford are manufacturers that spring to mind as producing exceptional manuals. In many cases, these factory worksiliconchip.com.au Volts, Amps, Ohms And All That In any electrical or electronic work on a car, you’ll come across words like resistance, current and voltage. Getting a mental grasp on what these terms means is vital before you attempt any electronic or electrical modifications. Hang in there – it’s simpler than you might first think. Voltage It’s very important that you have a good workshop manual available before you dive into the wiring harness. The factory manual is the best, well worth spending the dollars if you can get hold of it. shop manuals will be both expensive and extensive – eg, 10 or 12 volumes and costing up to $500. Even if you’re on a budget, we still recommend that you spend the money. It’s just so much easier to get things right if you have good information available to you. (And if you don’t want to spend the money, find your nearest TAFE that teaches automotive courses and see if they have a workshop manual in their library for your car.) Second-best after factory workshop manuals are the generic manuals produced by companies such as Gregorys and Haynes. These aren’t as detailed as the factory manuals but they will usually still provide enough basic information for you to trace the right wires. Don’t expect much discussion of how things work, though. Finally, you may have a car for which no English workshop manual exists. In this case, strive to get hold of at least a translated wiring diagram – you’re sure to be glad that you did. In this case, we’d suggest that paying up to $50 for a (clear!) diagram is a cost effective step – it will be that much easier to avoid mistakes which, after all, could be quite costly if you shortout the main ECU, for example. Doing It Let’s take an example – you’re fitting a LED mixture meter that siliconchip.com.au Everyone knows that a car’s electrical system uses a nominal voltage of 12V DC, while a wall power point has a voltage of 240V AC. But what does it actually mean? Like many electrical terms, it’s easiest to understand if an analogy is used – electrical voltage is a bit like fuel pressure in a fuel-line. A fuel pump in an EFI system pressurises petrol at about 30 psi, pushing it through the fuel line to the injectors. A battery produces an electrical pressure, causing an electric current to flow through a circuit. The higher the voltage, the greater the distance that an electrical spark will jump. The ignition system produces a voltage of more than 20,000V and this high voltage allows the spark to jump across the plug’s electrodes. Electrical pressure is measured in volts! The symbol for volts is “V”, so when we refer to 12 volts, we’re talking about 12V (usually from the car’s battery). Current Current is the amount of electricity flowing along a wire. Using the fuel line example, it’s like measuring how many litres per second are passing along the pipe. Current is measured in Amps. The symbol is “A” and a current of 20A means 20 amps. Wires that need to take a lot of current (like the one to the starter motor) are thick. Resistance Resistance indicates how hard or easy it is for a current to flow through a substance or circuit. Something with a really high resistance is called an “insulator” – it lets almost no current through it. On the other hand, anything which allows current to flow very easily is called a “conductor”. Normal copper wires within a car loom are good conductors, while the plastic covering around them is a good insulator – stopping the current from going where it’s not intended to! As the resistance goes up, the flow of electricity is reduced. And of course, there are lots of graduations between good conductors and good insulators. Resistance is measured in Ohms and the symbol for this is Omega (Ω). So when we refer to a resistance of 12Ω, it has a value of 12 ohms. Many engine management sensors operate by varying their resistance. A coolant temperature sensor, for example, usually has a high resistance at a low temperature and a high resistance at a low temperature. Complete Circuit Before there can be a flow of electricity, a complete circuit must be present. As the name suggests, the current does a complete loop – leaving one terminal of the battery or ECU, passing along the wire to the load or sensor, and then travelling back to the other terminal of the battery or the ECU. In a car, the return “wire” to the battery is often formed by the metal body (chassis). This is connected to the negative side of the battery and so the need for lots of earth return wires is removed. A poor earth connection, which might cause anything from bad headlight performance to poor EFI sensor operation, will present a much higher resistance than normal to the return current flow. In fact, the connection may even be intermittently good or bad, causing the symptoms to vary or to come and go. monitors the voltage readout of the oxygen sensor. The first step is to decide whether you’re going to tap into the sensor output at the engine bay end of things or at the ECU end. In one case, you’ll be working near to the oxygen sensor itself (which is in the engine bay or under the car) and in PERFORMANCE ELECTRONICS FOR CARS 33 Car Electrical Signals: Analog And Digital Explained There are two basic types of signals in car electronic systems – varying analog voltages and pulsed signals. The first is the easier to understand and measure. An analog voltage is one that steplessly varies as the parameter changes. For example, the air-flow meter in most cars has a voltage output that alters with engine load. At idle the voltage output from the air-flow meter might be 1.2V, at a light load 2V, at a heavier load 3.4V and at full load 4.2V. At “in between” engine loads, the voltages will be between these figures. Sensors that have analog voltage outputs include: (1) coolant, intake air and cylinder head temperature sensors; (2) most air-flow meters; (3) most MAP sensors; and (4) throttle position sensors. A normal multimeter can be used to measure these signals. The other type of common signal is one that it pulsed – ie, it continuously turns on and off at a rapid rate. For example, the signal from a road speed sensor might be a square wave that switches rapidly between 0V and 5V. At any point in time, the signal is either at 0V or 5V – there are no “in between” values. The way that the ECU makes sense of this signal is to look at its frequency – ie, how many times it switches between 0V and 5V (or turns on and off) per second. This is measured in Hertz – abbreviated to Hz. The old name for Hertz is “cycles per second” and in many ways this gives a better mental picture of what is happening – how many up/down cycles of the signal occur each second. The shape of the waveform is also very important in many sensing applications. For example, a crankshaft position sensor not only indicates the piston position (usually when No.1 cylinder is at Top Dead Centre, or TDC) but also indicates the engine RPM to the ECU. In the latter case, this is done by using the ECU to measure the frequency of the waveform coming from the sensor. The extra information can also be communicated by a change in the waveform. For example, if the waveform is being generated by a toothed cog passing a sensor and at TDC there’s a tooth on the cog missing, then the ECU will be able to sense the missing pulse. Sensors that have pulsed outputs include some air-flow meters and MAP sensors and all crankshaft, camshaft and speed sensors. What about when the ECU is sending out the pulsed signal? When the ECU is controlling something using a pulsed signal, there are two parameters which are critical. First, there is frequency. Just as with an input signal, how fast the output signal is being turned on and off is important. However, it’s the second parameter which is more widely used as a control variable – the duty cycle of the signal. Consider a square wave signal that is being used to open the injectors. When the other case you’ll be working near the ECU, which in nearly all cars is inside the cabin. There are advantages and disadvantages in each approach. Because the mixture meter will be mounted inside the cabin, if you tap into the loom near the sensor, you will then have to run a wire back into the cabin through a hole in the firewall. On the other hand, locating the correct sensor wire will be easier. In this case, we’ll assume that the connection will be made at the ECU. Here’s the procedure: •  Finding the wire: using the workshop manual, find out which wire carries the signal from the oxygen sensor to the ECU. You can either look on an overall ECU inputs/outputs diagram, in a table showing the same information, or under “oxygen sensor” itself. For this example, I’ll use a Mazda MX6 Turbo workshop manual – it shows that the oxygen sensor input occurs at ECU terminal 2D. The manual also says that when the engine is warm, this input will have a fluctuating voltage from 0-1V. The next step is to find where terminal 2D actually is on the ECU connector and a diagram shows this to be on ECU connector #2, one position in from the righthand, bottom end when viewing the plug from the ECU 34 PERFORMANCE ELECTRONICS FOR CARS Fig.4: an analog signal voltage varies steplessly. Here the output of a throttle position sensor can be seen – it is 0.5V when the throttle is closed and 4.5V when the throttle is fully open. At other throttle angles, the output voltage varies linearly between the two extremes. [Nissan] Fig.5: this diagram shows the waveform generated by one type of speed sensor. Its frequency (how many up/down cycles occur per second) changes with road speed. [Lexus] the current is switched on, the injector is open. When the current is switched off, so is the injector. But what propor- side, with the plug tabs uppermost. This step is very important – make sure that you check whether the plug is shown from the loom or ECU side and how is it orientated in that view. •  Checking it’s the right one: to check that you’ve found the right wire, two more steps should be taken. First, make sure that the wire’s colour code matches with the described plug location. In other words, if the oxygen sensor signal wire is supposed to be a shielded conductor with black insulation, make sure that the wire going into the designated connector placement actually is a shielded black wire! siliconchip.com.au Fig.6: this diagram shows how the duty cycle of the signal being fed to the power steering control valve decreases as vehicle speed rises. This change in duty cycle results in a varied average current through the valve – the lower the current, the heavier the steering becomes. [Holden] tion of the time is the injector on for? If the “on” time is the same as the “off” time, then the duty cycle is 50%. If it is on for three-quarters of the available time, the duty cycle is 75%. By varying the proportion of on and off times, the ECU can control the injector flow. Sometimes this approach is called “pulse width modulation” or PWM. A pulsed output signal can vary in both frequency and duty cycle – and sometimes both simultaneously. For example, the frequency with which injectors squirt is tied to engine revs, so as the revs increase so does the injector pulsing speed. However, as indicated, the duty cycle of that signal will also vary with engine load. While injector signals vary in both frequency and duty cycle, many other pulsed actuators use a fixed-frequency signal and only the duty cycle is varied. For example, the flow control solenoid in an automatic transmission or power steering system is likely to have a fixed frequency but a variable duty cycle. These valves aren’t “opened” and “closed” like fuel injectors; rather, the valve pintle hovers around mid-position, giving a flow that can be continuously varied according to an output from the ECU. Checking the shape of a pulsed signal waveform requires an oscilloscope. At the time of writing, hand-held portable oscilloscopes are still too expensive for amateur use (although prices are dropping rapidly). However, a good multimeter can be used to measure both the frequency and duty cycle of most automotive sensor signals. Second, does the wire have the correct signal on it? In this case, the voltage from the sensor with the engine warmed up should be in the 0-1V range (in fact, it will be varying around 0.5V). You can check this by connecting the multimeter’s red probe to this wire (either by using a thin piece of stiff wire to push into the ECU connector from the back or probing directly through the insulation of the signal wire) and earthing the other multimeter probe; eg, on the case of the ECU. •  Making the connection: in the case of a mixture meter, the signal wire from the oxygen sensor to the ECU is not broken – the mixture meter simply taps into the signal wire. There are a few ways in which this connection can be made, including crimp-on clips. However, our preference is to do it like this: (1). Use a razor blade or sharp utility knife to remove a section of insulation (easier to do if the insulation is sliced around in two circumferential cuts about 5mm apart and then the separated insulation sleeve pulled off). (2). Remove 10mm of insulation from the new wire and then firmly wrap the bared section around the original loom wire at the point where the insulation has been removed. siliconchip.com.au When selecting a multimeter, make sure that it has temperature, duty cycle and frequency measuring capability in addition to the “normal” volts, ohms and amps ranges. This unit is measuring the injector duty cycle – in this case, 4.1% at idle. (3). Solder the two together and make sure that the join is shiny (which indicates a well-soldered join). (4). Wrap the join with high quality insulation tape and then use a cable-tie to stress-relieve the new joining wire, so that a tug on the new wire doesn’t pull on the new connection. Taking this approach has a number of benefits – it doesn’t weaken the original electrical connection, it can be reversed, and it gives excellent mechanical and electrical connection to the new wiring. In this example of mixture meter wiring, you’ll now also need to find earth and ignition-switched battery voltage connections to power the meter. Again, you should be able to be find these on the ECU without too much trouble. Conclusion Making electronic modifications to your car is practically impossible unless you have a good multimeter and know how to use it. In addition, you must have access to wiring diagrams for the car. With those two things in the bag, the next step is to go make  some changes! PERFORMANCE ELECTRONICS FOR CARS 35