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C4 battery drain/voltage

 
Old 01-14-2019, 09:43 AM
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RAZORVETTE76
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Default C4 battery drain/voltage

So have had the inside of the car apart fixing the heater control box by the pedals, lost vacuum there. Got it all fixed on that part. Started car like normal to make sure that I could get air coming out of other vents besides the defrost. Anyways, I decided I would go ahead and put my new headunit and speakers and amp in. It already had an aftermarket head unit and amp in it, but it was wired horrible and I just re-did it all and here is where the fun started. Now the only thing I really changed wiring wise other than ran all new stuff, was the ground for the amp and the radio. Now the dam car sits over night and wonít start. I used a volt meter last night at 8:30 to measure voltage at the battery and itís was 9.98 volts. Come out at 6:30 am and do it again to see how much itís lost and the volts where at 11.5. Car should have started at that point but nope!!! So if I had a drain on the battery, would I have not lost volts over night?? I have checked in the dark in the garage to see if any door lights, under hood light or any other light is staying on in the car and none. The car was fine and never had a starting problem till this. So also as I mentioned above, tried to start it when the volt meter said 11.5 this morning and not only did it not start, the battery voltage dropped back down to 9.98. So in my eyes, trying a drain test, using the a volt meter and pulling fuses is not going to do any good cause itís not losing volts over night. One last thing, I can push it out of the garage and hook cables to my truck, donít t even have to start my truck and the vette will fire right off. So after this long winded soap box, could it be the battery is just toast??

Last edited by RAZORVETTE76; 01-14-2019 at 09:45 AM.
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Old 01-14-2019, 09:51 AM
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How old is the battery? Once a battery drops below 10 volts, I don't trust it anymore. If it's a one time thing, fine, I'll charge it and monitor it. If it happens more than once, especially while starting, it's likely toast. If you have a charger, charge it up and see if it hold, as it could be it was just low on charge, and working on the stereo was enough to drop it to empty(interior and hood lights draining it).
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Old 01-14-2019, 11:41 AM
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Paul Workman
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Considering each of six cells in a (car) battery develops 2.1 volts, a reading of ~ 10 volts immediately after attempting to start the engine (especially) is a classic symptom of one of the battery cells is likely shorted. Need a new battery. The fact that connecting another 12v battery (in parallel) with yours, and the car immediately starts is supporting evidence of a battery problem (yours).

Also, a direct current measurement is usually a far better way of determining if you have unexpected or excessive drain on the battery when the car is at rest.

Position the test leads as shown and position the VOM switch to (dc) A (amperes). Then, after removing one of the battery cables, connect one test lead to the battery cable and the other to the battery post. A C4 reading is typically .025 to .035A (or 25 to 35 mA).. That is the normal "keep alive" current used to maintain the ECM memories and radio pre-sets, etc. Some manuals (not necessarily C4 FSM sources) will say 50 mA or less is "normal". But, every C4 I've tested is @ 35 mA or less, 25(ish) mA is typical. More than that - i.e., anything approaching 1 ampere + requires pulling fuses, one at a time to find the guilty suspect (circuit).

I can't tell for sure w/o testing myself, but from your description of the symptoms my money would be on the battery has a bad cell or at least is on the brink! Take the car to you favorite auto parts store (Autozone does a good job, as does Farm and Fleet, I have found) and have the battery LOAD TESTED. Then you'll know for sure what is what!.)



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Old 01-14-2019, 12:05 PM
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Originally Posted by Paul Workman View Post
Considering each of six cells in a (car) battery develops 2.1 volts, a reading of ~ 10 volts immediately after attempting to start the engine (especially) is a classic symptom of one of the battery cells is likely shorted. Need a new battery. The fact that connecting another 12v battery (in parallel) with yours, and the car immediately starts is supporting evidence of a battery problem (yours).

Also, a direct current measurement is usually a far better way of determining if you have unexpected or excessive drain on the battery when the car is at rest.

Position the test leads as shown and position the VOM switch to (dc) A (amperes). Then, after removing one of the battery cables, connect one test lead to the battery cable and the other to the battery post. A C4 reading is typically .025 to .035A (or 25 to 35 mA).. That is the normal "keep alive" current used to maintain the ECM memories and radio pre-sets, etc. Some manuals (not necessarily C4 FSM sources) will say 50 mA or less is "normal". But, every C4 I've tested is @ 35 mA or less, 25(ish) mA is typical. More than that - i.e., anything approaching 1 ampere + requires pulling fuses, one at a time to find the guilty suspect (circuit).

I can't tell for sure w/o testing myself, but from your description of the symptoms my money would be on the battery has a bad cell or at least is on the brink! Take the car to you favorite auto parts store (Autozone does a good job, as does Farm and Fleet, I have found) and have the battery LOAD TESTED. Then you'll know for sure what is what!.)




plenty of threads and u tube videos on this subject....all say battery should test 12.5 or .6 before testing....just did my 85, 33 mv autozone can tell you quickly and for free.....
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Old 01-14-2019, 01:33 PM
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Novaks47, it never had a problem starting till I messed with the stereo. It always started and never gave me a problem. I did run the battery dead while I was messing with getting the old stereo out and putting the new one in. I know I should have disconnected the battery and for some reason I forgot to. Anyways Iíll try and get the battery tested and move from there. Just donít want to buy a new battery and fry it to. Thanks for the the the amount of help guys.
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Old 01-14-2019, 03:21 PM
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So just ran to the house for lunch and put the volt meter back on the battery and the same 11.5 volts it had this morning at 6:30. So I figure if there was enough of a drain on the battery to cause it to go dead over night, it would have shown less volts after sitting there from 6:30 to 12:45. Also, can anybody tell me what the rapid clicking is coming from under the passenger side dash when I try to start it?? Thanks guys.
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Old 01-14-2019, 03:34 PM
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Goldcylon
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I think you have a dead cell. The IP and the car will make interesting noises and displays on the IP if you don't have a fully charged battery, I have never heard of an Aftermarket Stereo causing this much drain over night. That clicking you hear is the battery not strong enough to turn over the car.

Last edited by Goldcylon; 01-14-2019 at 03:36 PM.
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Old 01-17-2019, 08:44 AM
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Thanks for all the help guys. Sure enough it was a dead cell in the battery. Put a new one in there and the car actually starts faster and idles better. You guys rock!! Now to get the interior put all back together and get my iggee covers on the seats and drive....
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Old 01-17-2019, 09:18 AM
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Thanks for closing out the post to help the next guy. Glad to hear you got it sorted out! GC

Last edited by Goldcylon; 01-17-2019 at 09:18 AM.
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