Why LESS voltage at battery terminals when engine heats up? - Ford Mustang Forums : Corral.net Mustang Forum
 
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post #1 of 13 Old 09-09-2002, 05:57 PM Thread Starter
 
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Question Why LESS voltage at battery terminals when engine heats up?

Ok, some of you are aware that I've been tracking an electrical problem with my 94 for some time now. I've been getting a "check engine" light, the car's idle jumps up to 1500 rpm's then stalls. Been to the dealer... $350 and a new O2 sensor later THEY say it's fixed. Wellll, 4 days later same deal. I take it back and they NOW say it's a bad eec. Sheezz I can throw parts at it too and save $83/hr in labor! SOO, I'm diagnosing the problem myself and here's what I've come up with....

The code I pulled is 511 which is for a "bad eec, replace" as the manual says. Ok, thinking I've figured that out, here's the next problem....

When my car is first started the "VOLT" gauge reads in the "R" when cold and all accessories are on. As the engine heats up and all the accessories are on the voltage drops to "N". Now when cold the reading I get at the battery terminals is 14.6vdc. Good. When it heats up I get a measly 12.5vdc. Bad! Barely enough to charge the batt. I've changed the voltage regulator and it seemed to help a bit but it still drops into the "N". I tried a trick the dealer said to do and that's turn the key to the "on" position but don't start it. Then touch something metal to the alt. pulley/bolt to see if it's magnitized. This checks to see if there's anything wrong with the rectifier/circuits inside. All is ok cuz I get a magnitized alt nut. What else could be causing this? Would a bad alt show up when it heats up? How about other charging system components?? HHEELLPP!!!!!! I think this is the cause of all my problems!

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post #2 of 13 Old 09-09-2002, 11:54 PM
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I'll give it a shot.

First, Your alt is only going to charge the battery if it needs a charge. Thats the purpose of the voltage regulator. After the car starts, its basicly running off the alt.

Take the alternator off and take it to a NAPA, Autozone, or someplace that can test it for free. No backyard stuff. It needs to be tested properly. Ensure that all your ground connections are ON and TIGHT. No fuzzy monkies on the terminals too. Check for corrorison on your cables. Take a test light and attach the ground to the negative post on your battery and touch the case of the alt to see if it is internally shorted. But most of all, have it tested!
Hope this helps...

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post #3 of 13 Old 09-10-2002, 10:55 AM
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Agree with above post. When it get hot it has more resistance, so with a bad alt, loose wire, ground, heat will make the problem worse. Get the alt checked, tell them the problem and have them put a load on it more than once, to heat up the alt.

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post #4 of 13 Old 09-11-2002, 05:05 PM Thread Starter
 
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I'll agree that as the alt heats up the resistance within also increases. But the idea that the alt KNOWS when the battery NEEDS a charge is false. The regulator "regulates" the charging system from spikes that can fry the computer, and other electronical components. It acts like a holding tank between a pump (aka alt) and demand source (aka the car). The tank keeps the thru-put (current/voltage) steady and blip free. If this were true then the alt/charging system would be connected and operating in conjunction with the EEC. It's not, they're are both stand alone systems. The alt should ALWAYS put out between 14 and 15 vdc no MATTER what temp the engine is operating at. This is according to the FORD manual for the Mustang. So I guess my next step is to test the alt under cold and hot conditions to see if it's putting out the max amps/volts.

Thanks for the replies!!!
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post #5 of 13 Old 09-11-2002, 05:26 PM
 
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""The code I pulled is 511 which is for a "bad eec, replace" as the manual says. Ok, thinking I've figured that out, here's the next problem....""


Do you have a chip?? If so, that is probably why you are getting code 511. I have a chip and I get that code everytime I pull codes. been like this for the last 3 yrs since I got the chip.
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post #6 of 13 Old 09-11-2002, 07:49 PM
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Hi there,
I agree w/Nitro Snake, if you have an aftermarket chip then you'll get code 511. This code is meaningless if you have a chip. See ya. Michael Plummer

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post #7 of 13 Old 09-12-2002, 01:44 AM
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94GoezQuik, I think you might be confusing the regulator with the diodes... At any rate, i'd have the alt tested to ensure its operating properly. Plus, that'll eliminate one piece of the puzzle. Hope you get it fixed, and when you do, post it here so we can all see and take note.
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post #8 of 13 Old 09-12-2002, 05:42 PM Thread Starter
 
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I do have an Autologic chip dyno tuned at LaRocca's Performance in NJ. Now the chip is over a year old and this new problem just arose? Why now and not when the chip was first installed??

I do agree that I need to get my alt tested. And when I finally figure out all this crap I'll post my results.
BTW, Is there any way I can test the EEC to see if it's bad?? I did remove the chip and I still triggered the C/E light.
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post #9 of 13 Old 09-13-2002, 08:39 PM
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All this testing and diagnosis and you haven't mentioned your grounds being clean or the condition of your cables and terminals.

I doubt your EEC is bad. Have the battery checked. Have the alt. checked. Check t he damn grounds. Add an additional ground between the frame and the negative battery terminal. If that seems to help, chances are you have a grounding problem. And finally, don't take your car to a dealer to have it worked on. You could have taken that $83/ hr and bought some tools and fixed it yourself. Or find a local independent mechanic, if you can't/don't want to work on it yourself.

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post #10 of 13 Old 09-14-2002, 01:05 AM
 
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Quote:
Originally posted by 94Goezquik
I do have an Autologic chip dyno tuned at LaRocca's Performance in NJ. Now the chip is over a year old and this new problem just arose? Why now and not when the chip was first installed??
Did you pull codes when you took the chip out? If I take my chip off, the code 511 goes away.

electrical problems suck! I had a problem one time, if I turned the key to the on position (not started)... the car would go into a KOEO test all by itself I went over every wire in the car I think for that one!!

good luck!!

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post #11 of 13 Old 09-16-2002, 06:15 PM Thread Starter
 
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The ground connections seem ok. I cleaned the ground strap between the engine and frame, nada. There is a secondary ground factory installed off the neg battery cable. It looks good. I physically removed the chip and STILL the "check engine" light came on as it has been. Removing the chip was one of the first things I've done. As of 2 weeks no light....
To refresh all who have donated their time on this....
Before I had this problem I had driven into a large puddle, causing the "voltage" gauge to go wacky and shoot up into the "L" on the gauge. If I remember correctly I did smell a slight burning oder coming from the dash. Then the next day the alt made a squeaking sound.... About 3 weeks later is when the electrical issues came up. I think I fried the alt, which spiked the eec.
Anyone agree?? No fuses blown which doesn't make sense....
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post #12 of 13 Old 09-16-2002, 07:20 PM
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I will put money on the fact that it is your alternator....you should test it immediately.

whatever you do, dont buy a cheapo one from pepboys or autozone unless you like to change them frequently...Im on my 5th in 1.5 years. If you do decide to get one from there, get one with a lifetime warrenty.

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post #13 of 13 Old 09-18-2002, 09:01 AM
 
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Quote:
Originally posted by Nitro_Snake


Did you pull codes when you took the chip out? If I take my chip off, the code 511 goes away.

electrical problems suck! I had a problem one time, if I turned the key to the on position (not started)... the car would go into a KOEO test all by itself I went over every wire in the car I think for that one!!

good luck!!
hey man i'm having the same problem. i drove through some pretty deep water when it rained the other day and when i start the car it goes through the KOER self test and starts flashing all the codes. can you point me in the right direction for the stuff you checked/repaired? thanks.
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