Mechanics

MITSUBISHI ECLIPSE SENSOR PROBLEM

2001 Mitsubishi Eclipse • 70,000 miles

With the discovery of 1.4volts supplied to the crank shaft sensor, in the "run" position, as in diagnoistic testing? This has led to two ignition circuits failing. GM and MITUBISHI. Does this coil get energised by some ECM failure, I think not. Is this happening to others? JEFF ANDREWS
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Jeff A.
November 1, 2012.




Don't have a clue what you're asking. Are we talking about a Mitsubishi product? Where does the GM reference come in? Are you talking about energizing the ignition coil or the coil inside the crankshaft position sensor?
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Caradiodoc
Nov 1, 2012.
The car was running fine, to the shop. The rear spark plugs were replaced, it started, ran for several minutes then suddenly died. Then trouble shooting turned up a fault with the PCM to distributor power transistor fault, no spark.I went to the shop to find out more.I saw that the ignition key was in the on position for some time, which I never do. This is a standard practice when using the computer tools. Brought the car home by tow truck, as every test had been done to find the trouble, and the PCM to distributor wire was said to be grounded.I was there when the crank sensor was tested, it was sending signal.I had the car brought home, tested the ignition power transistor by using the digital multimeter, grnd to grnd and positive to distributor plug blu/blk wire useing the diode function, it read.769, which is ok.I rechecked the crank position sensor, it read 14m ohms, that is bad. Why it showed good is probably athe shop is part of the info I am trying to asess. The ignition fuse at the drivers dash end showed a 10 amp ignition fuse blew too, this is part of the explaination. The key being left on for a long time, being supplied with 1.7 volts. To the crank sensor is of question

Tiny
Jeff A.
Nov 2, 2012.
This ipod phone screen is hard to use. The failure of the ignition parts is related, maybe, as failure occurred when. Friend turned my trucks ignition on to listen to the radio, rather than using the acsessory position. That maybe coincidence, leaving whatever ignition parts to heat up. On the Mitsubishi Eclipse, I found the fuel pump relay warm, after several minutes in the on position, as done when diagnoising with the computer. So two parts went bad, the10amp fuse and the crank sensor coil. The way to avoid this is my point. My experience is old school, if the ignition key is turned to on, then power is going through the circuit.I found voltage to the crank sensor, and the relay, which seems okbut why all the trouble is what I intend to figure out so others can avoid it. Humbly offered, Jeff

Tiny
Jeff A.
Nov 2, 2012.
The testing of the fuse, with a light probe showed good. Testing with a digital meter showed 26 ohms, it had blown! Point for the good guys! Next, what caused it to blow after starting?Could the coil have failef, then testing?Or some grounding of a hot ignition wire have happened? Hmmm? Well the fuse test must be done with the digital meter, and same with coil to crank position too! The fuse is odd. So in short start diagnoising with the simplest tools and simple problem, you know the basics. Jeff

Tiny
Jeff A.
Nov 2, 2012.
First of all, you know way more about electrical theory than almost all other visitors to this site. That makes my job more fun. Second, it sounds like you know more about this model than most mechanics, so probably the best thing I can do is make a few observations that might have some value.

My background is Chrysler, but Mitsubishi and Chrysler do things very similarly. Mitsubishi makes a lot of parts for Chrysler, in fact, my favorite radio to repair is a Chrysler cd / cassette combo built by Mitsubishi.

As for the crankshaft position sensor, if you're measuring voltages on it, I know it will have three wires. One is the feed for it and that's usually 5.0 volts, but it could be 8.0 or 10.0 volts. That will be present anytime the ignition switch is in the "run" position, and leaving the ignition switch on won't harm it. It's on regardless if the engine is running or not; it doesn't care. Another wire is the ground, but it goes to ground through the Engine Computer so that circuit can be monitored. It will typically have 0.2 volts. I never tried to measure the signal voltage, but if you do, I suspect you will see it vary from near 0.5 volts to 4.5 volts if you slowly turn the engine by hand. Crank and cam sensors always have a magnet in them, and something with notches on the engine disturbs that magnetic field as they pass it. That induces a voltage which is amplified by the circuitry inside the sensor, and that's why they can have a varying output voltage while the engine is standing almost still but turning very slowly.

The sensors with two wires rely on the movement of whatever it is with the notches to disturb the magnetic field fast enough to generate a pulse of voltage in the coil of wire around the magnet. Speed is a factor in how much voltage is developed, just like in a generator, so there will be 0 volts coming from that type of sensor until the engine is turning at cranking speed. Since no voltage is applied to them, there is no difference between ignition switch off or ignition switch on / engine not running.

The next comment has to do with what Chrysler calls the automatic shutdown (ASD) relay. Mitsubishi might call it an "ignition" relay or "fuel pump" relay but I believe they do the same thing. The Engine Computer turns that relay on when it sees engine rotation, and it knows that by the pulses it receives from the cam and crank sensors. Once it turns that relay on, that sends current to the ignition coil, injectors, and in Chrysler's case, the oxygen sensor heaters, alternator field, and fuel pump or separate fuel pump relay. That's a safety design and is real effective and reliable. In the case of a crash that ruptures a fuel line, the engine can't run with no fuel pressure so it stalls. When it stalls there's no cam or crank sensor pulses so the computer turns off the ASD relay. That turns off the fuel pump so it doesn't continue dumping raw fuel onto the ground creating a fire hazard.

The clue to a problem with the sensors is there will be no voltage to the ignition coil or injectors if the ignition switch is on but the engine is not running. My reason for sharing this is everything in those circuits should be dead when the ignition switch was left on so nothing should be overheated. On much older cars it WAS possible to have current flowing through the ignition coil with just the ignition switch on but that rarely damaged them. I suspect in your case there may have been something that was planning on failing soon anyway and the least little extra nudge sent it over the edge. Leaving the ignition switch on wouldn't cause a part to fail but it might hurry one up that is about to.

Don't have an answer on your fuse issue. I usually check for voltage on both sides. You can't go by the resistance checks on the crank sensor because there's a lot of circuitry inside it that you'll be measuring through. That won't work so the 14 meg ohms isn't valid. You have to test for an output signal. If I were to do that, I'd use an oscilloscope that I use for tv repair, but it's just as correct to use a digital voltmeter, but there are some stipulations. First of all, they are designed to measure 60 hertz AC voltage. Crank sensors usually develop three or four sets of pulses spaced far apart during each crankshaft revolution. You'll get some pulses much higher than 60 hertz, then a relatively long pause before the next set of pulses arrives. The display on the meter will be bouncing around a lot. It may show some voltage but the actual value means nothing. Some meters read hertz directly without regard to the voltage level of the signal but even those don't work on crank sensors. They'll pick up a series of three or four pulses, then a long stretch of silence, then pulses, then silence. The meter will get dizzy trying to display that.

I'm not real familiar with the ignition power transistor. I know what it does but as far as diagnosing it, that was always a part of Chrysler's Engine Computer and rarely caused a problem. The only thing I could suggest that might apply is to check anything that can be replaced or unbolted to see that there is heat-sink compound there to help transfer heat away. If you understand Ohm's Law, you know that voltage times current equals power which means heat is generated. Those switching transistors are designed to be turned fully on or fully off, never partway in between. At fully off there is no current flow so 0 amps times any voltage equals 0 watts and no heat buildup. That one is easy to understand. But, when it's fully on, there can be lots of current flow but since it's practical a piece of wire with no resistance, no voltage is dropped across it. 0 volts times any current again equals 0 watts and no heat. The problem comes in when there's a little voltage and a little current at the same time. THEN you have power dissipated and heat generated, and you gotta get rid of that heat because that is the deadly enemy of semiconductor electronics. Circuitry problems can reduce how effectively that transistor turns fully on or off. The voltage spike from the ignition coil's primary winding has an effect too but I can't remember the reason. Other circuitry in the driver module generates heat too.

Anyway, there's my thoughts on the subject. Take anything you might find useful.

Caradiodoc
Nov 2, 2012.
Hi, refreshing to read, you are. A great resource and I can appreciate your dedication, passion. The crank sensor coil is a solenoid, two wires, low micro amps, so not much heat, reliable. And on the pulse rate, it would be 3xRPM on a v6. Pick up a new 4channel digital storage NICOLET if needed. You are astute. The crank sensor coil, made of say.012"wire, should come in at appx500 ohms, nice and easy to check. The testing of the transistor base control is like a diode, should be done at the distributor. The plug is pulled out of the distributor, identify transistor signal wire, The challenge on advanced systems is to stay simple logical as the computers do their magic, it is suppose to be reliable and userfriendly, not a confusing monster, . You are spot on, please tell me you are appreciated. Humbly offered Jeff

Tiny
Jeff A.
Nov 2, 2012.
Yes I do have a lot of problems knowing things, but I keep to myself, let others learn, or ask. So when I run in to difficulties, it is a real pain in the plug to find one as learned as you, I tip my hat to you sir!J

Tiny
Jeff A.
Nov 2, 2012.
Happy to be of service. I'm an expert on what I know, ... Duh! All else I leave to others.

And you don't have to call me sir. "Sir" was my dad. I'm on a first name basis with my students.

Now, ... Carry on, and have a dandy night.

Caradiodoc
Nov 2, 2012.

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