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Car has been running great this summer but while out for 2 hour drive last weekend it wouldn't start after a 10 minute stop. When I turned the key, it turned over once then stopped. I tried again but it just went click. Luckily I was on a flat piece of road so I was able to bump start it. As soon as I got home I grabbed my voltmeter and measured the voltage at the battery terminals while still running.


I got 12.0 V at idle and 12.4 V when I revved the engine. I parked it then boosted it directly to the starter and block and then to the battery terminals. No difference, started right up which eliminated the starter. I then removed the battery and hooked it up to my Optimate 6 charger for 24 hours. Battery measured 12.56 V after charging. I put it back in the car and it started just fine. The voltage then measured 13.45 V at idle and dropped to 13.14 V at any RPM over idle then back up to 13.45 V at idle. It's a 2 year old Interstate Battery.


I plan on taking it to my friend's shop Thursday morning. He'll poke around to see if he can sort it out. 






1975 - 2002 - Sabine - Jade

2010 Toyota Matrix XR

Remember: RACECAR spelled backwards is RACECAR

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3 minutes ago, PaulTWinterton said:

Sounds to me like a bad connection somewhere.  It should read 13+ consistently.  After you fiddled with it, it was ok.  Check your wiring on the back of the alternator.  Make sure ALL connections for the Alt and Battery are clean and strong.


And the voltage regulator.




Stop reading this! Don't you have anything better to do?? :P
'73 320i /M2 2.5; '85 ///M635CSi ; '73 320i ugly car; '99 AMG C43


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Especially check:

1. the three prong plug on back of the alternator--it's supposed to have a wire bail (clip) to hold it in place; that's often missing and will allow the plug to loosen, causing a poor contact and sub-optimal charging.

2. the ground wire that connects one of the bolts on the alternator with its mounting bracket on the block.  It's a heavy brown wire with ring terminals on each end.  The wire may look good but have corrosion and/or broken wires under the terminals and their insulators.  If this ground wire is broken or even partially so, the alternator has a very dodgy path to ground, which can cause poor charging.




'69 Nevada sunroof-Wolfgang-bought new
'73 Sahara sunroof-Ludwig-since '78
'91 Brillantrot 318is sunroof-Georg Friederich 
Fiat Topolini (Benito & Luigi), Renault 4CVs (Anatole, Lucky Pierre, Brigette) & Kermit, the Bugeye Sprite

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On 8/10/2016 at 8:08 AM, Justin99 said:

If your battery is reading 12.54v immediately after charging for a day it may be in the process of failing. It should read 13+v for at least an hour or so after being charged.

Sent from my iPhone using Tapatalk


Well, we have a winner! "Justin99"


I dropped my car off at my friend Angelo's shop this morning. He has a small garage in mid-town Toronto where he works with his father Paul. They've got two hoists and can fit a total of 3 cars in the shop. He called me to say he checked the battery and alternator and guess what, it was the battery.


The thing that threw me off was that for some reason, I thought the Interstate battery was 2 years old. Angelo called Interstate guy to drop off a new battery. When he got there he said the battery was 8, not 2 years old so no longer under warranty. My bad... My buddy asked me if I wanted a new one for $215 plus tax and then quickly suggested I go to Costco instead. Yeah, $90 sold! 


I dropped by his shop with the battery and he was busy so I grabbed a wrench and installed the new one. The best part is when I pulled out cash to pay him for his time, (he spent more than an hour on the car) Angelo said "no, you don't owe me anything". That's when his Dad chimed in with "small regular coffee". I'm going to bring him one tomorrow morning.


It's so hard to find good, honest people like these guys. Anyway, had I known the battery was 8 years old (and not 2), it would have moved it up on the list of probable causes. 


It's funny how we sometimes over-think these things!

Edited by Senna27

1975 - 2002 - Sabine - Jade

2010 Toyota Matrix XR

Remember: RACECAR spelled backwards is RACECAR

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