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Old 12-15-2013, 06:36 PM   #1
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1990 foxbody voltage issue

Any one who can help? starting w issue one. When coming to a stop and pushing the clutchin, my idle will drop so low that vehicle cuts off. Turns right back on though. Cleaned mass air flow sensor. Checked tps. Im lost? This brings me to my next question. When the vehicle is at idle my alternator doesnt seem to doing its job. Very low voltage on my instrument panel. Checked batt. Good. Had alt tested. Siad it was good but border. When car is moving no prob. At idle my car stereo will not even work properly. Anyone know where else to look. I also adjusted my tps down to .75v dc
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Old 12-15-2013, 07:00 PM   #2
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Check your IAC for stumbling idle.

Your TPS is out of range.. needs to be at least .88.

Voltage fluctation problems in these cars can normally be traced to bad grounds- one from the firewall to back of the engine is for the dash. Secondary ground post by the starter solenoid for the neg battery. ground for neg batt cable to the block. If you have a 130 amp alt you must also install another 4g wire ground wire- I did it from the A/C bracket to the 2nd ground post.

If you are running the stock alt, the wiring is notorious for failing and starting a fire. The stock alt also is inadequate for even a stock car IMO. Do you have U/D pulleys by chance?
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Old 12-15-2013, 07:54 PM   #3
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What do you have that is drawing amps while the car is running? Such as electric fan, what type of electric fuel pump, what do you have for a stereo, A/C lights, ect.? Then what do you have for a alternator and where is the battery located? Then what do you have for pulleys, under drive crank and lastly what size alternator pulley?
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Old 12-15-2013, 07:55 PM   #4
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ALt upgrade!! go through all your charging/battery wiring ad replace it. Old cables have higher resistance and cause these issues.
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Old 12-15-2013, 08:12 PM   #5
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I was thinking of changing the alt to the 130 just to have a stonger alt anyhow. Appears to b the original. Just bought the car and am not only looking to restore but learn about motors as well. Motoer has been swapped and appears to very nice but appeared that someone bacame hurried towards the end and lert lots of bad wiring behind. I did notice when i checked the tps for a good ground i was reading roughly 2k when i should of had a dead short from green to chasis correct? Battery has been moved to the back of vehicle and im not sure about the pullies, how would i b able to tell. Thnks for all your help. I hope to get this thing top shape one day. Lights and heat drop voltage dramatically.

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Old 12-15-2013, 08:13 PM   #6
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Quote:
Originally Posted by girard90foxbody View Post
Any one who can help? starting w issue one. When coming to a stop and pushing the clutchin, my idle will drop so low that vehicle cuts off. Turns right back on though. Cleaned mass air flow sensor. Checked tps.
Any TPS voltage between .5 and 1.25 is considered good by an A9L computer, but you really want to be inside 0.6 to 1.1 volts. If it is inside that range, adjusting makes no difference.

Mustang throttle position sensor

The IAC would be more of a worry to me, as would the throttle stop.

Quote:
Im lost? This brings me to my next question. When the vehicle is at idle my alternator doesnt seem to doing its job. Very low voltage on my instrument panel. Checked batt. Good. Had alt tested. Siad it was good but border.
There is no such thing as good but border. Test it yourself.

Testing battery and charging system

Quote:
When car is moving no prob. At idle my car stereo will not even work properly. Anyone know where else to look. I also adjusted my tps down to .75v dc
I don't know why you would do that, but it is still within acceptable range. Ideal would be about .8 to .85 volts, not that it means anything much if you are at .75 or 1.0 or anything away from the edges.

I would look at the IAC and closed throttle adjustment screw on the TB.

Before you rush out and start changing parts, you were asked good questions. Do you have under drive pulleys? Do you have any stuff that greatly increased electrical system load demand? The stock alternator is plenty big if you did not add a bunch of current demand from power hungry things, and if it is good. It is pretty tough for one to be good and test "borderline". If it tests borderline, and if the test setup is good, that means it has a bad part inside.

But before you change parts, do you have any high current loads on it or do you have under drive pulleys?

The battery should hold everything at idle for some period of time, as long as the battery is fully charged. Measure the battery voltage as shown on the link I posted. That will tell you if something is messed up far better than Autozone.
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Old 12-15-2013, 08:21 PM   #7
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Quote:
Originally Posted by girard90foxbody View Post
Any one who can help? starting w issue one. When coming to a stop and pushing the clutchin, my idle will drop so low that vehicle cuts off. Turns right back on though. Cleaned mass air flow sensor. Checked tps. Im lost? This brings me to my next question. When the vehicle is at idle my alternator doesnt seem to doing its job. Very low voltage on my instrument panel. Checked batt. Good. Had alt tested. Siad it was good but border. When car is moving no prob. At idle my car stereo will not even work properly. Anyone know where else to look. I also adjusted my tps down to .75v dc
is this an original stock car?

first thing you do is check codes.
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Old 12-15-2013, 08:32 PM   #8
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Not original car. 302 bored to 306. Lots of upgrades.
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Old 12-15-2013, 11:21 PM   #9
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ya think maybe you should tell us all your upgrades?
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Old 12-15-2013, 11:22 PM   #10
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ya think you should check for codes before spending money?
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