alternator vs. sensors? - Ford Mustang Forums : Corral.net Mustang Forum
 
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post #1 of 8 Old 02-14-2003, 12:04 PM Thread Starter
 
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alternator vs. sensors?

The one thing I'm not that good at is electrics and wouldn't ya' know...

Here's the scenario:

1) Driving back from a night out, "check engine" light comes on. Only at idle RPM. Voltmeter dropping off at same time.

2) Get home, pop hood, alternator is smokin' hot. So I figure I got a bad alternator

3) Pull codes. Get 636 and 117 indicating bad readings from tranny and engine coolant temp sensors. NOT what I expected...

4) Engine is hard to start. Turn on key, voltage is low. After a few tries it starts and shows the system drawing a charge (i.e. voltage high)

5) Check engine light never came back after that first night, but I've just run the car since, not actually driven it...

In no case is the "high" or "low" voltage outside the normal range, just higher/lower than usual (i.e. dead center)

So I still think I got a bad alternator, but wanted some thoughts from y'all before I go plunk down for one:

a) is it possible/likely that the bad sensor readings are a by-product of abnormally low/high voltage in the system because the altie's going bad?

b) should I mess with changing the regulator first, or just go get a whole new alternator and not mess with it...

c) should I replace the sensors, or wait and see if they "come back?"

Finally, yes, I know the whole testing procedure for an alternator, but it'll cost about as much as a new altie to buy a good ohm/voltmeter that'll handle it -- my little digital guy would probably explode if I used him... And, like I said, I'm just not overly confident in this area.

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post #2 of 8 Old 02-14-2003, 12:05 PM Thread Starter
 
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Sorry... It's a 1995 GT convertible.

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post #3 of 8 Old 02-14-2003, 12:12 PM
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It's a bad battery. The alternator is just working overtime and hard to keep up with the vehicle's needs.
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post #4 of 8 Old 02-14-2003, 12:19 PM Thread Starter
 
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Thanks Wazee. DO you think the bad sensor codes are part of this, or I actually got bad sensors?
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post #5 of 8 Old 02-14-2003, 12:30 PM
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The codes you got are probably from not warming the engine up properly before getting the codes. The coolant temp sensor may have not been in the proper range of resistance when the test was run. Same with the other. Could be bad too.
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post #6 of 8 Old 02-14-2003, 12:33 PM Thread Starter
 
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Okay. Maybe shoulda mentioned that the ECT sensor seems to genuinely not be working -- the fan kicks on and off (low, high, off, low, high, off) repeatedly when the engine runs -- hot, cold or otherwise. Will probably replace just to be on the safe side. The tranny oil sensor, OTOH... That looks like kind of a ***** to deal with so may wait and re-test after other issues fixed.
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post #7 of 8 Old 02-14-2003, 12:35 PM
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The little digital thingy will do just fine. check battery voltage with key off. Then start the car and check voltage. Look for 12-12.5 off and 13-14 on. If you have close to 12 with on then it's the alternator. I would not rule out the alternator yet. Set your voltmeter to 20V DC and check it. You can't blow a voltmeter unless you use it to check current (amps)
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post #8 of 8 Old 02-14-2003, 12:39 PM
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there are two sensors for engine coolant. One is for the gauge on the dash. The other one is used by the computer. One is in the lower intake on the battery side of the distributor. The other is on the heater tube just above the thermostat(computer) I could be wrong.
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