Phantom Posted July 14, 2015 Share Posted July 14, 2015 (edited) Sent my clock off to get it rebuilt a few months ago. Got a new movement in it, got it reinstalled, and it appears to be working great. I haven't had a working clock in about 15 years so I didn't realize that the clock would nearly drain my Red Top battery in about 3 weeks. I went out to the car and it, to quote a Princess Bride line, was "mostly dead". Mad Max was able to give it just enough energy to get the car to start on the second try. Then it got interesting. Once the car started the idle went up to between 2,500 & 3,000 RPM. After a minute or so I could get it down to around 2,000 - 2,500 RPM. I'm running things through my mind and I'm just not figuring out how this could be happening. The car has an LS1 with a mechanical throttle cable. It is NOT drive by wire so why the high idle? I got out, popped the hood and checked the throttle position on the engine and it was at the normal idle stop -but idling over 2,000 RPM. I drove the car about 4 miles until it was up to temperature and it still had the high idle - so I shut it down. About 15 minutes later I restarted it and it was fine - everything normal. Idle back down to around 800 RPM and normal throttle response. I figure the extremely low voltage start somehow messed with the ECU but how did it get the idle up so high on an engine with a mechanical throttle? Edited July 14, 2015 by Phantom Quote Link to comment Share on other sites More sharing options...
z240 Posted July 14, 2015 Share Posted July 14, 2015 I hate problems that just "go away". So hard to diagnose. Vacuum leaks (air entering after the carb throttle plates) and ignition timing also affect engine speed. Quote Link to comment Share on other sites More sharing options...
NewZed Posted July 14, 2015 Share Posted July 14, 2015 Modern ECU's will hold the idle speed up to charge the battery, among other reasons. 2500 seems high but who knows what your algorithm is. And the idle speed was probably controlled by the Idle Air Control Valve. Lets air past the throttle blade, electrically controlled by the ECU. Quote Link to comment Share on other sites More sharing options...
Miles Posted July 14, 2015 Share Posted July 14, 2015 (edited) The red top is a cranking battery and , as I learned, does not hold up to electric fans, amplifiers, lighting and small parasitic loads like clocks and stereos. I'll be going to a yellow top when my red top fails. Edited July 14, 2015 by Miles Quote Link to comment Share on other sites More sharing options...
Phantom Posted July 14, 2015 Author Share Posted July 14, 2015 Interesting, I have had this battery over 10 years now and my car has a 500 watt sound system I play all the time, mostly with the engine running but occasionally for 30-60 minutes without the engine running. This is the first time it's gone down on me. It was in the shop several months ago, before the clock, and they managed to kill it. It charged back up and seemed OK but maybe not. 10+ years may have it at its life expectancy. Quote Link to comment Share on other sites More sharing options...
Phantom Posted July 14, 2015 Author Share Posted July 14, 2015 Interesting, I have had this battery over 10 years now and my car has a 500 watt sound system I play all the time, mostly with the engine running but occasionally for 30-60 minutes without the engine running. This is the first time it's gone down on me. It was in the shop several months ago, before the clock, and they managed to kill it. It charged back up and seemed OK but maybe not. 10+ years may have it at its life expectancy. Quote Link to comment Share on other sites More sharing options...
Phantom Posted July 14, 2015 Author Share Posted July 14, 2015 Modern ECU's will hold the idle speed up to charge the battery, among other reasons. 2500 seems high but who knows what your algorithm is. And the idle speed was probably controlled by the Idle Air Control Valve. Lets air past the throttle blade, electrically controlled by the ECU. Good information. Thank you. Quote Link to comment Share on other sites More sharing options...
Miles Posted July 14, 2015 Share Posted July 14, 2015 Interesting, I have had this battery over 10 years now and my car has a 500 watt sound system I play all the time, mostly with the engine running but occasionally for 30-60 minutes without the engine running. This is the first time it's gone down on me. It was in the shop several months ago, before the clock, and they managed to kill it. It charged back up and seemed OK but maybe not. 10+ years may have it at its life expectancy. My second red top refused to charge after the car sat for the winter. Quote Link to comment Share on other sites More sharing options...
Phantom Posted July 14, 2015 Author Share Posted July 14, 2015 I've found that it pays to have battery tenders for the winter months and also a really good battery charger that can "recondition" a battery. My Suburban battery almost went dead three months ago. It was a 95 month old 96 month battery. I ran the "recondition" mode on it with the charger and then ran the regular charge mode. It has been doing great since then. It won't work on anything but a lead-acid battery because the "recondition" mode causes the lead oxide build-up on the plates to slough off. 3 of 4 of my cars have lead-acid b batteries in them so I'm thinking I might want to recondition those batteries once a year and see if it will significantly extend their life. Won't work on Gel batteries like the Optima Red Top and I don't think it will work on Lithium batteries either. Quote Link to comment Share on other sites More sharing options...
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