Multiple sensor and injector failure codes

What you're describing is a typical result of of an electrical problem that can all be related to one or two wires. Many sensors are fed from the same 5.0 volt source, then multiple wires split off and go to each one. A common cause of this is a stretched connector terminal, particularly after a connector has been unplugged. Corrosion can get in there too and often not cause symptoms until the plug is disturbed.

The clue here is a voltage that is changing. Since most sensors are fed with 5.0 volts, if you find less, follow that wire back to the next accessible test point until you find the spot where you DO have 5.0 volts. That is how we narrow down the location of a broken or poor connection.

You can't read injector voltages with a voltmeter. When they turn off, they develop voltage spikes just like an ignition coil does on a gas engine. Your meter is reacting to those spikes.

Fuel metering is controlled by how long the injectors are held open by the Engine Computer. They're typically supplied with 12 volts, then the computer grounds the second terminal for a carefully calculated period of time to hold them open. That time changes to control fuel delivery, and can be viewed as "injector ms" meaning milliseconds, on a scanner that displays live data.

I don't have a listing for these fault codes. Do you have a description of each one? If there is one that makes reference to one sensor, like the throttle position sensor or a temperature sensor, we can start with that one and take some voltage readings. Since everything was working properly before the repairs were done, it's likely there is going to be a cut wire or a grounded wire.

I'm familiar with the intake air temperature sensor, so lets start with that one. Unplug the two-wire connector, then measure the voltages on those wires with the ignition switch turned in. You must find 5.0 volts on one of them and 0.2 on the other. Now plug it back in and back-probe through the rubber seal to take the readings again. The ground wire should still have 0.2 volts, but the signal wire should have dropped from 5.0 volts to something between 0.5 and 4.5 volts. Typically you'll find around 3.0 volts.

If you ever find 0.0 volts on the signal wire, there's a break in that wire. If you ever find 5.0 volts on both wires, there's a break in the ground wire.

The next step would be to pick another fault code and test the circuit it refers to. I can't find any service literature though to tell you what to look for. The intake air temperature sensor works the same way on almost all cars. That's why I picked that one to start on.

Every intake air temperature sensor I'm familiar with has only two wires or it's incorporated into the mass air flow sensor. 3.3 volts is a typical value on the signal wire but it shouldn't be bouncing around.

Most MAP sensors have only three wires. The signal wire starts out fairly high with the engine not running, but it shouldn't be all the way up to the 5.0 supply voltage. That wire should drop to around 2.0 volts as soon as the engine starts.

What I would do is monitor that IAT wire with the bouncing voltage, and flex the wire harnesses to see if you can find an area that makes it hold steady at 0.0 or 5.0 volts.

I've never seen any of these sensors on any car that have anything other than 5.0 volts applied to them, so all those readings you found higher than that confuse me. Any chance you're using an auto-ranging voltmeter and are overlooking when it switches to the millivolts scale? I hate auto-ranging meters for that reason, and don't own any.

The glaring problem is there's no change in the MAP reading between ignition on and engine running. That can be caused by a disconnected vacuum hose for that sensor, or a break in the signal wire. To verify a break, measure that voltage at the computer like you did, then at the sensor. Both should be exactly the same.

Since I'm not familiar with your car, let me double-check a few things. Does it use a negative ground, meaning the battery's negative cable is bolted to the engine and body? Do you have your meter's negative probe on ground too?

I don't know much about lambda sensors, but when there's only two wires to a sensor, one is ground and the other is the signal wire. If you understand electrical theory, this will make sense. The ground wire goes back to the computer, then through some monitoring circuitry before it actually gets to ground. That's why you'll find very close to 0.2 volts instead of 0.0 volts on it.

The signal wire is fed 5.0 volts through some sensing circuitry, to the sensor. With the sensor unplugged, creating an open circuit, the full 5.0 volts will be seen at the connector. When the circuit is completed by plugging the sensor back in, some of that 5.0 volts is dropped across the sensing circuitry inside the computer, and the rest is seen at the sensor. The voltage seen at the sensor is dependent on whatever it measures. If that is temperature, the sensor's resistance goes down as the temperature goes up, so the voltage across it will go down at the same time. If it measures something that changes when the engine is running, such as intake manifold vacuum, the voltage has to change at the same time.

Most MAP sensors are plugged directly into the manifold now like you said, to eliminate that hose, but there has to be a change in the signal wire's voltage as soon as the engine starts. The difference here is those will always have more than two wires. In this case the ground and 5.0 volt feed wires will always stay the same, but you have to see a change at the signal wire. When there's no change between start and run, there has to be a break in the signal wire, or the sensor is defective. The only other possibility is no vacuum is getting to the sensor, which only happens when they use that hose, and it has a break in it.

To have many voltages change, especially when disconnecting and reconnecting the plug, is reminiscent of the huge problem GM had with their Engine Computers in the late '80s and early '90s. I suspect, by the way they acted, they developed numerous bad solder connections inside. We used to see that all the time on tv modules that were machine-soldered. A real lot of engine performance problems were solved by replacing those GM computers, and it's a big reason why so many mechanics fall back on computers as the big suspects now.

If you can get the circuit board out of the housing, a local tv repairman can inspect it visually for broken connections. Also look closely at the connector pins for signs of corrosion. Terminals in connectors can stretch too and make poor contact, but that normally isn't a problem with Engine Computer terminals because they're pretty high-quality and they don't get taken apart very much.