Starting Problems Again...need help!

warment · 09-13-2001, 04:33 AM

After fully charging both batteries on my 1973 911T and re-installing them in my car, I was unable to start the car up. I did a voltage check on each battery, and received a reading of 10.57 volts(is this normal? The charger gave me a green light indicating a full charge) at the positive terminal of each battery. I then performed a voltage check on the "hot" connection to the starter motor(which is directly connected to the positive terminal of the left front battery) and received a reading of 7.57 volts. This appears to be a sign of a bad direct wire between the battery and the starter. My question then is, what gauge wire runs directly from the battery to the starter? It appears to be bigger than 8 gauge to me, possibly 6 or 4 gauge. Could someone please tell me what size this wire is? Thanks a lot.

Bill

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William Armentrout
1973 911T
2.7 carerra rs specs
www.geocities.com/william_armentrout

Rot 911 · 09-13-2001, 05:16 AM

Bill, you have a dead cell in your battery if it is reading 10.57 volts. Your battery charger will give you a fully charged reading, which only means that cells that will take a charge are charged up. Very strange that you got this reading on both batteries. A normal battery should show around 12.5 volts fully charged. Before I even messed with the starter or its wiring, I would make sure I have a good battery showing 12.5 volts. For what it is worth, as your probably know, you really only need to be running one battery in your 911.

Kurt V
72 911E

warment · 09-13-2001, 05:22 AM

What could cause a bad cell in both batteries? I think it is very, very odd that this failure happened on both batteries. I have only had them for a little over a year, and they really have not been used that often, as I have been working on sheet metal repair on the car, etc. What kind of voltage should I be receiving at the starter? Should it be very close to the voltage as seen at the battery? Thanks for your input.

Bill

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William Armentrout
1973 911T
2.7 carerra rs specs
www.geocities.com/william_armentrout

stlrj · 09-13-2001, 08:35 AM

Unlikely a bad cell in both batteries, but since they are connected in parallel, they both appear bad.

Isolate the batteries before checking the voltage to find the bad one.

Joe

Rot 911 · 09-13-2001, 09:59 AM

Bill, I agree with Joe, isolate the batteries and make sure they are both bad. I don't know enough about batteries to tell you why the cell may have gone bad. As to voltage at the starter, yes it should read close to what the battery voltage is.

Kurt V
72 911E

Early_S_Man · 09-13-2001, 10:37 AM

Bill,

Examine both batteries closely for any bulging ... which can cause shorts in the adjacent cells! This can be caused by overcharging, so check your alternator/regulator output for too high output Voltage ... anything above 15 Volts is too high and causes boiling and overheating, and possible bulging/buckling/shorting of cells. And, shorted cells in batteries connected in parallel subject to oveercharging for an extended time is not out of the ordinary!

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Warren Hall
1973 911S Targa
1992 Dodge Dakota 5.2 4X4 parts hauler

warment · 09-13-2001, 01:41 PM

Thanks for the tips. Nobody told me what gauge wire the car has from the battery to the starter though? I am sure that this wire needs replacement, so I would really like to get a new one.

Bill

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William Armentrout
1973 911T
2.7 carerra rs specs
www.geocities.com/william_armentrout

Early_S_Man · 09-13-2001, 01:53 PM

Bill,

Very unlikely that you need a new cable ... pull off the positive battery connector by loosening the two M6 bolts that clamp the connector to the cable, then clean both connector and bare cable end with wire brush. Should the cable end be damaged, cut an inch or so off squarely and reclamp the connector. Check both ends of all ground straps for corrosion ... at battery and between body and trans crossbar mount.

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Warren Hall
1973 911S Targa
1992 Dodge Dakota 5.2 4X4 parts hauler

warment · 09-13-2001, 02:20 PM

Warren,

I installed a new trans ground strap yesterday, cleaned all ground points, cleaned all terminals, and wire brushed the end of the cable running from the starter directly to the battery. This problem has gotten progressively worse in the past few months.

Could you please tell me if the wire running directly to the starter is 2, 4, or 6 gauge? I have looked everywhere and cannot find the answer. I kinda think that this wire is partially to blame, but probably not the only cause. I am going to replace the wire running between the 2 batteries as well. Thanks again for the tips.

Bill

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William Armentrout
1973 911T
2.7 carerra rs specs
www.geocities.com/william_armentrout

Superman · 09-13-2001, 02:33 PM

Bill, of course it will not hurt anything to replace those cables, it may not be necessary and very probably is not the cause of the problem. I suspect that if we just put my battery in your car, it would start just fine. And it would run fine for a long time if your alternator is doint its job.

I can assure you, with positive certainty, that 10.57 volts WILL NOT start a car. And if your batteries can not hold at least 12.5 volts after a deep charge, then they are junk and must be replaced. I'm absolutely sure.

You only need one battery, not two. When the new battery (or batteries) is in, hook a volt meter to them. They WILL be above 12.5 volts. Then start and run the car. With the engine running, you should see between 13.5 and 15 volts. If this is not the case, then it was your alternator that killed your batteries.

I'm not discouraging you from replacing cables. But I am assuring you that pure copper cables 6" thick welded directly to the battery and starter will not start the car on 10.57 volts.

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'83 SC

warment · 09-13-2001, 05:30 PM

It looks like you guys were right...my batteries are toast. After another volt test, here are my results:

Left battery(separated from right battery) showed 10.61 volts

Right battery(separated from left battery) showed 11.81 volts

Left and right battery hooked together in parallel(key in off position) showed 11.41 volts. As a side note, the voltage at the starter read 11.41 volts with the batteries in this position. My past attempt at checking the voltage at the starter was incorrect because I had the wires configured incorrectly on my voltmeter/ohmmeter!(Stupid!) What do you know...Warren was right again when he said that he highly doubted that the direct wire from the battery to the starter was bad! Thanks Warren.

Left and right battery hooked together in parallel when trying to start car showed 7.81 volts

Left battery separated from right battery after several start attempts showed 8.58 volts

Right battery separated from left battery after several start attempts showed 9.54 volts

It looks like I will be purchasing new batteries(or a new single battery if I can find a suitable sized battery to fit inside a battery box with high enough cca). Could you guys recommend one? Does Optima make a batt to fit inside of my battery box? I have heard that they make some really good batteries. I would prefer a sealed battery.

After all of my learning, I still consider myself a "newbie"...

Bill

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William Armentrout
1973 911T
2.7 carerra rs specs
www.geocities.com/william_armentrout

stlrj · 09-14-2001, 07:22 AM

If room was available, you might invesigate the possibility of installing two 6V deep cycle marine batteries in series for more CCA .

Joe

RoninLB · 09-14-2001, 10:06 AM

Deep cycle marine batteries probably not a good idea. Call Optima, tell them what your needs are and they will probably suggest the Red battery.

Early_S_Man · 09-14-2001, 12:32 PM

Bill,

There are several sizes of conventional 'Group' designations that will fit properly into the battery box, including Group 41 batteries that have up to 88 Ampere-hour capacity. A battery shop should have a catalog with dimensions that would aid finding a replacement.

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Warren Hall
1973 911S Targa
1992 Dodge Dakota 5.2 4X4 parts hauler

warment · 09-14-2001, 08:40 PM

Thanks Warren. I'm going tomorrow to find a new pair.

Bill

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William Armentrout
1973 911T
2.7 carerra rs specs
www.geocities.com/william_armentrout

djZuvuya · 09-15-2001, 04:46 AM

another reason why you had low voltage is that when batteries are in parellel it acts like a voltage divider. they should be hooked up in series.

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Zuvuya
85 carrera targa

Early_S_Man · 09-15-2001, 05:02 AM

Bill,

The reason I mentioned the 'Group 41' battery is because it is one of the few with a low profile that can slide all the way into the battery boxes ... but they are approximately 12" long, so about 5" or so will stick out where the tool kit and charcoal cannister normally are laying. But, it is a relatively easy thing to rearrange things in the trunk to fit the larger battery. The benefit is that one Group 41 takes the place of both of the pairs' capacity with power to spare ... an extra 16 Ampere-Hours, to be specific, so the rearrangement is well worth it! The positive cable to the second battery needs to be disconnected or removed entirely.

Zuvuya ... I hope you are not serious suggesting that the two 12 Volt, 36 Ampere-Hour batteries in '69 thru '73 911 models should be connected in SERIES!!! Two 12 Volt bateries in good shape, fully chargerd will give 12.8 Volts or so, and deliver the full 12.8 Volts to the starter when connected in parallel ...
EVERY TIME! That is, provided the terminal connections and battery ground cables (and transaxle-to-body ground straps) are clean and tight!
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Warren Hall
1973 911S Targa
1992 Dodge Dakota 5.2 4X4 parts hauler

[This message has been edited by Early_S_Man (edited 09-16-2001).]

RoninLB · 09-15-2001, 06:13 PM

I would use a battery isolator if I had 2 batteries in my 911

RoninLB · 09-15-2001, 06:21 PM

2 12 volt batteries in series to start a car works in emergency situations. Risk is destroying starter if not done quickly.

Rot 911 · 09-16-2001, 07:41 AM

Bill I run a group 41 Interstate battery that fits as described by Warren. Never had a starting problem with only one battery. By the way, the battery you have that is registering 11.81 volts may still be good. Try charging that battery by itself and see if it will take a full charge, i.e. 12.5 volts.

Kurt V
72 911E