1988 Dodge Lancer SMEC

I had half a reply typed, then my computer crashed. If I seem to stop in the middle of something, I'll be back to finish it after I buy a new computer!

Chrysler had extremely little trouble with computers before the '96 model year so that should be your last suspect. Code 46 refers to battery voltage. Start by measuring it while the engine is running. It must be between 13.75 and 14.75 volts. Do not ever try to run the engine on just the alternator with the battery disconnected. That will make the voltage go too high, set that code, and will usually destroy all the computers and any bulbs that are turned on.

You also have a code for the intake air temperature sensor. Failures of that sensor are unheard of unless they're damaged from rough handling. Codes are set when it is unplugged with the ignition switch on or when there's a bad connection in one of the two wires or in the plug.

The oxygen sensor code is just saying the sensor isn't doing anything. Lets forget that one for now until we get the rest of the codes sorted out. Black smoke from the exhaust is often caused by a MAP sensor starting to fail or a leak in the vacuum hose going to it. That sensor could be plugged into the logic module behind the right kick panel, otherwise, on newer cars it was on the passenger side firewall. There was a recall for those on the firewall to add a tee in the hose at both ends, then connect the extra fittings together with a second hose. The two hoses were just running in parallel, but the thought was there would be air circulation in there to prevent gas fumes from condensing and blocking the hose.

Do you have a scanner or did you get the codes by cycling the ignition switch?

The battery is the key component in helping the voltage regulator hold system voltage down to a safe level. If there is a high-resistance connection, that is going to reduce its ability to do that, and it could be responsible for the high voltage code. It depends on how the battery failed the test. If it just couldn't maintain 9.6 volts during the load test, that is a capacity issue and not related to its involvement with the voltage regulator. If the voltage was low under no load, as in around 11 volts or less, that is related to a shorted cell, and there is something else causing the fault code.

When the battery is disconnected to be replaced, that is going to erase all the fault codes. At that point, see which codes set again.

For the MAP sensor, check if there is a tee fitting in the hose, near the sensor. If there is, and you follow those two hoses, they should reconnect in another tee at the other end near the intake manifold. If you don't have that second hose and two tees, the recall was never performed. The black smoke from the tail pipe is a sign of running much too rich. The MAP sensor has the biggest say in how much fuel enters the engine. If there's a leak in the vacuum hose going to it, it will interpret that as low vacuum due to load on the engine and the need for more fuel.

You really need a scanner to see what the Engine Computer is seeing from the MAP sensor. A voltmeter will work well enough to see that it's working, but not well enough to use the results for diagnostics. The sensor is fed with 5.0 volts, then it puts out a signal voltage between 0.5 and 4.5 volts, approximately. Anything outside that range is what triggers a fault code. Where the elusive running problems come in is when the sensor reports the wrong value, but it's within the acceptable range. There may not be a fault code but the engine will be getting the wrong amount of fuel, usually too much.

The signal voltage is typically around 4.2 volts when you turn on the ignition switch. That represents barometric pressure, and that value goes into the Engine Computer's memory. Once the engine is running, you can expect to see around 1.5 volts. Higher vacuum equals lower voltage. You can watch that happen with a voltmeter while you apply vacuum from a hand vacuum pump to the port on the sensor.

Usually when MAP sensors fail, they go from good to bad within a day. They don't take long to fail completely. The clue is the engine will not stay running unless you keep moving the accelerator pedal. As long as the computer sees a change in throttle position, it will keep supplying fuel.

Here's a few things to consider. First of all, when you disconnected the battery, the Engine Computer lost its memory. It has to relearn "minimum throttle" before it will know when to be in control of idle speed. Until then it may be hard to start unless you hold the accelerator pedal down 1/4", it won't give you the nice idle flare-up to 1500 rpm at start-up, and it will tend to stall at stop signs. To meet the conditions for the relearn to take place, drive at highway speed with the engine warmed up, then coast for at least seven seconds without touching the pedals.

Next, when you have an idle speed that's too high, you need a scanner to see why that is occurring. The Engine Computer will set the automatic idle speed motor to one of 256 positions as necessary to keep the idle speed as desired. The scanner will display "AIS Steps" For a properly running engine you'll find it at around step 32 in neutral. If idle speed is too high and it's near step 0, the computer is trying to lower the idle speed without success. Typically that's due to a vacuum leak. If the steps are unusually high, like step 50, that would be in response to a misfiring cylinder, but when the actual idle speed is too high too, the computer is raising the speed in response to something, and that is typically because of a low temperature sensor reading or it is anticipating a load on the engine like running the air conditioning compressor. The compressor runs in cold weather in the defrost mode too, so if the AC is disabled or non-functioning, you will still get a change in idle speed when you turn on the defroster.

You may want to have the alternator professionally load-tested for maximum output current and "ripple" voltage. Your maximum current should be around 75 amps, as I recall. If the most you can get is around 25 amps, exactly one third of its rating, it has a defective diode inside. That means you're losing one of the three output phases. During the missing phase, output voltage will drop a lot and that will confuse the Engine Computer. It will also interfere with sensor readings. That can have an affect on the MAP sensor, and wrong readings from it, by as little as.05 volts, will have a big affect on fuel metering. The alternator has to be tested on the engine. Too many people take them off and haul them to an auto parts store for testing. Those testers aren't strong enough to run an alternator under maximum load for a few seconds. That takes five to eight horsepower. Test benches have up to one horsepower motors. All they'll tell you is if you have SOME output. You need to know how much output.

On a related note, the alternator is mounted on rubber bushings. To complete the circuit for the output current to flow, there is a ground cable or a braided ground strap bolted to it and to the engine block. Check that cable to see if it is corroded. If just a few strands are all that's left, you won't get full output current through it. The clue there is when running the engine with many loads on, like head lights heater fan, and rear window defogger, you will measure a voltage between the alternator housing and the engine block or battery negative post. That voltage should be 0.0 volts. To find one or two tenths of a volt is normal but it shouldn't be much higher than that.

Temperature sensors have an extremely low failure rate because there's just one component in them. Almost all failures, except on Fords, are due to corroded connector terminals, a break in a wire, or it was unplugged while the ignition switch was turned on. Corroded terminals have to get bad enough before a code will set. Until then the added resistance of that corrosion will raise the voltage the computer sees, and higher voltage translates into lower temperature. If the computer thinks it's 20 degrees colder than it really is, it is going to add too much fuel to the calculation. Liquid gas does not burn. It just goes out the tail pipe, wasted. Gasoline has to be a vapor to burn and turning into a vapor is harder in colder temperatures. Years ago we accounted for that by adding a choke. That dumped way too much fuel into the engine in hopes a high enough percentage would vaporize to burn and make sufficient power. That isn't such a big problem when using fuel injection, but throttle body injection systems run at a pretty low pressure and atomizing the fuel isn't very efficient. We still need to add fuel, and the throttle body temperature sensor, intake air temperature, (IAT) sensor, or battery temperature sensor are the ones that tell the computer how much to add.

Regardless if there's a code or not, you need a scanner to see what temperature the computer thinks the incoming air is. That value will stay fairly constant once the engine is running, and the coolant temperature reading must be the same before the engine is started. That one, of course, will go up as the engine warms up, but the two sensor readings must be the same at start-up of a cold engine.