Hold on a minute. My head is spinning. I didn't understand more than ten percent of what you said.
The oxygen sensors are by far the least important sensors on the truck as far as making the engine run right. You can't measure their signal voltage because it bounces above and below 0.5 volts roughly twice per second. Digital voltmeters don't respond fast enough, and if they did, all you'd see is a random jumble of numbers. All four O2 sensors have a ground wire for their internal heaters. The heater feed wire comes from the ASD relay. That is the same circuit that feeds the ignition coil pack, injectors, alternator field, and fuel pump or pump relay, so if that wire is grounded, it will kill everything on that circuit and you'll have a crank / no-start problem. That was common on a few car models where the wiring harness would fall down onto hot exhaust parts. The intermittent short caused a fuse to blow, and that made it a permanent failure, meaning the engine would not run intermittently at times. You had to replace the fuse first.
The second ground wire actually goes through the Engine Computer, then to ground, so the computer can monitor it. That's the ground for the sensing element.
The two rear O2 sensors have absolutely nothing to do with engine performance. They only monitor the efficiency of the catalytic converters. Most of the time the only way you will know there is a problem with any O2 sensor is by the Check Engine light turning on and reading the fault code.
The front O2 sensors switch between "rich" and "lean" roughly twice per second, then the Engine Computer calculates the average and tweaks the fuel / air mixture by plus or minus a maximum of about ten percent. It does that by varying the length of time the injectors are pulsed on.
It's actually the MAP sensor that has the biggest say in fuel metering calculations. Even when it fails, there are ways to keep the engine running. It will cause insufficient fuel for the engine to run, but it will never cause NO fuel, and it has nothing to do with spark or loss of spark. Fuel metering is further tweaked according to readings from the coolant temperature sensor, ambient air temperature sensor, and throttle position sensor. Here again, none of those have anything to do with loss of spark.
On your diagram, you have the entire ASD relay circled in purple. Does that mean you have 12 volts on the lower right dark green / orange wire? That should only be there during cranking. If you have it there all the time, there is something wrong with your meter setup.
Getting back to my story about the O2 sensor with a grounded heater wire, here's a way to check for that, or to check the rest of that circuit. Remove the ASD relay, then in its socket, jump terminals 30 and 87 together with a light bulb. I use a brake light bulb with two jumper wires, and I use a pair of spade terminals. If you use an actual test light, be careful to not poke the probe in so far that it stretches the terminal in the socket. That can cause future intermittent problems. The ignition switch doesn't have to be on. With the light connected, the bulb will be full brightness if there is something shorted to ground on the dark green / orange wire. Your test bulb will limit current to less than an amp so no wires will overheat.
The ignition coils and injectors will be turned off at the computer so they won't be drawing any current. The alternator's field circuit draws a maximum of three amps, but it too is off when the engine is not running. On your truck, the fuel pump and its relay are a totally separate circuit so energizing the dark green wire won't send any current to the pump. Since no current will be flowing through the ignition coils, injectors, or alternator field, no current will be flowing through the bulb, and it will be off.
You can prove to yourself how this works. Go to the dark green / orange wire at any convenient point, ... Any injector or either coil pack, and measure the voltage. You'll find perhaps not the full 12 volts, but close to it. Now, while you're measuring that voltage, use a jumper wire to ground that wire, either at the meter's probe or at any other injector or coil pack. You'll see the voltage drop to 0.0 volts and the light will become full brightness; both indicating there is a short to ground on that circuit.
That trick is one I learned when repairing tvs and I adapted it to finding shorts on cars by energizing the circuit without blowing fuses over and over.
One thing I wasn't aware of but will really work to our advantage is the fuel pump is an entirely separate circuit. When they do it that way, both the fuel pump relay and the ASD relay are grounded by different terminals at the Engine Computer, but internal to that computer, both circuits are still in parallel. That means the computer turns both relays on at the same time. If you can find that dark green / black wire at the pump's connector, monitor that while you're cranking the engine. A test light works best for that. If you find steady 12 volts during cranking, then we have to look at the ignition coils or injectors. I expect you're going to find the same 12 volts for one second when the ignition switch is turned on, then the same 0 volts during cranking, as you found on the dark green / orange wire. If you do, we're back to the cam and crank sensors.
Forget trying to measure a signal voltage at the cam and crank sensors. Both of them develop a square wave that goes from 0.2 volts to either 5.0 or 12 volts. (I can't remember since it isn't something we measure). If you put your meter on AC volts, you'll get a reading but it is meaningless. Meters are designed to read a 60 Hz sine wave. You have a square wave that typically is four pulses, a long gap, then another four pulses. I don't know how a V-10 differs from a V-8, but there has to be a series of pulses indicating a piston is nearing TDC on the compression stroke, and a different series of pulses indicating which piston is coming to TDC. You don't have a steady signal, you don't have a 60 Hz signal, and you don't have a sine wave.
If you try to measure a pulse with the DC volt scale, digital meters all take a reading, analyze it, then display it while they take the next reading. It may take a reading one time when it's at 0.2 volts, and the next three times when it's at five volts. All you're going to see is numbers jumping around. Unless you have a friend who is a tv repairman and has an oscilloscope, there are only two ways to tell if the cam and crank sensors are working. One is if the ASD relay is turning on during cranking, and the other is to view those sensors on a scanner, listed as "No" or "Present".
I'm starting to get myself confused now, so sorry if I mentioned this already or if my train of thought got derailed, but you're wasting your time with most of what you're doing. If you have no spark and no steady 12 volts on the dark green / orange wires, we need to stick with the cam and crank sensors. You CAN measure the power supply voltage to them. That's the violet / white wire at each sensor. That will be 5.0 volts, 8.0 volts, or 12 volts, and it has to be the same at both sensors. The black / light blue at both sensors should have 0.2 volts. Those are their ground wires, but they don't go directly to ground. They go through the computer, THEN to ground. There's monitoring circuitry in the computer, hence the 0.2 volts instead of 0.0 volts.
If you're having a communication problem with the scanner, that is usually due to a blown fuse, and depending on which circuits it feeds, it can also be responsible for a dead ASD circuit. You have the luxury of having a pile of accessible fuses to test. In tvs with integrated circuits that can have over 80 terminals, we have to look at the voltages on every one. For computers on cars and trucks, they tell us when there's a problem with a circuit, so all we need to look at are the "powers and grounds". Use your diagram to see which terminals should have 12 volts and which should have ground. Most commonly, (again, from memory), there will be four ground wires and four 12 volt feed wires. One 12 volt feed is constant. That is for fuel trim and fault code memory. One gets 12 volts when the ignition switch is on. That one tells the computer to turn on and do its thing. I mentioned that the ASD relay turns on the voltage to the injectors, ignition coils, etc. Well, there's one more place it goes. That is to another terminal at the computer. That 12 volts tells the computer that the relay did indeed turn on and there should be voltage to the rest of the circuit. Somewhere along the line is a fourth 12 volt terminal that I think is the reference for the alternator's voltage regulator. I don't remember right now where that 12 volts comes from or what other circuits might be involved, but if that was missing, typically you'd have an over-charging condition, but the engine would run.
If any of those 12 volt lines is missing, follow that back to see where it comes from.
The grounds are a little trickier. Two are called "signal grounds" and two are "power grounds". The signal grounds are for the sensors and the power grounds are for high-current stuff like injectors and ignition coils. All you need is one strand of wire to be not yet corroded away, and that wire will test good with an ohm meter. That is not accurate. Instead, turn the ignition switch on, then measure the voltages on the ground wires. You should see 0.0 volts, but don't panic if you see a little, as in a few hundredths of a volt. That voltage is likely stray electromagnetic interference being picked up by the meter leads. Each pair of ground wires are in parallel, so both would have to be broken or corroded to have voltage appear on them at the computer. Problems with the ground wires is very uncommon.
The reason for two separate ground circuits is there is always a little resistance in any wire, and current flowing through a resistance causes a voltage to be dropped across it. Every time an injector or an ignition coil turns on or off, there is a sudden change in current flow, and therefore a sudden tiny voltage pulse dropped cross the ground wire. If you'd watch those pulses on an oscilloscope, they might only be a few hundredths of a volt, but if sensors shared those ground wires, those tiny voltage pulses would appear on the sensors' grounds, and that would show up in their signal voltages too. Those tiny voltages would mean quite a bit to a MAP sensor.
Sunday, October 30th, 2016 AT 12:52 AM