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By ianmatt - 8 Years Ago
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This is driving me crazy. I am not a wiring / electrical guy at all. I did instal my tach and pertronix. For some reason when I turn on my lights my rpm drops by almost 200. Its not wanting to make my truck die. It didnt seem as bad before i swapped the eddy with the holly. Now I finally got the 600cfm Holley totally dial and this is happening. Where do i start? What could it be? Anyone have this problem? All I want to do is drive my truck.
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By charliemccraney - 8 Years Ago
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Automatic or manual transmission? What is the voltage at the battery when it occurs? Does it happen at any rpm or only a particular range?
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By ianmatt - 8 Years Ago
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manual, yes any rpm, much more noticeable at low idle. Reg idle is 650 and it will drop to 500 and below and want to die. I dont know what voltage is at battery. I know my mechanic said a while back that the battery was a battery for an RV and I should think about getting a different one but that it would work for now. I have never had battery problems. What is the battery of choice for a modified 292 with pertronix, cam, headers...?
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By charliemccraney - 8 Years Ago
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Regarding the battery, as long as your're not after a stock look, you want the battery with the most cold cranking amps that will fit. There is no go-to battery.
What it sounds like is happening is that turning on the headlights is causing a significant voltage drop, which is affecting the ignition. So the first thing to do is to make sure that all grounds and connections are good. If the problem still exists, then next is to verify that the generator or alternator and battery are functioning correctly. An easy way to get an idea about this is to measure the voltage at the battery, one with everything off, another with everything on but the lights, and another with the lights.
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By 62bigwindow - 8 Years Ago
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I would look at the charging system first. Then the battery. Alternator or generator?
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By ianmatt - 8 Years Ago
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Alternator is new. 6 months old and installed during engine build. I have always noticed a slight drop when lights are on however its as of recently its been lots worse. I wonder if i messed up a ground wire somewhere while swapping carbs. I may buy a new optima red top battery this evening and see what that does. Thanks for the help folks. I'll keep you posted.
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By charliemccraney - 8 Years Ago
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Check your grounds and do a voltage check before you spend money on a battery you might not need.
I forgot to include that you should charge the battery before performing any of the tests. If the charging system is not working, the battery will be low, making it appear to be bad when it might not be. So put it on a charger to make sure it is fully charged then do your tests.
If you have a shop manual, some of the tests may still be applicable even though it is no longer the stock generator. So have a look at the electrical trouble shooting section as well. If you have a shop manual for a newer vehicle with an alternator, that trouble shooting section may also help.
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By ianmatt - 8 Years Ago
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I am curious if its possible for you to provide some specifics as to where to look / check the grounds? I am not good with electrical.
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By charliemccraney - 8 Years Ago
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I won't be much help with that. My truck has not been stock in that regard since I've had it. Even so, if yours is a different year or model it may not be the same. The negative battery cable goes somewhere, so that is one. There should be one from the block to the body or frame. Might be others.
Which vehicle and year so others might be able to help?
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By MoonShadow - 8 Years Ago
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Are the alternator brackets powder coated or newly painted? The alternator ground through them and the block to the chassis. I would find all the ground straps and the negative cable connection and take them apart. Make sure the contact surfaces are metal to metal. Where is your battery mounted? If you don't find a ground connector on the block add one. Usually they bolt to one of the not used 3/8 bolts on the intake next to the accelerator linkage mount. Run a ground from there to a bolt on the firewall. I run my battery in the trunk of my Vicky. I used heavy gauge cable for the positive side and grounded to the frame at the rear. All connections were scraped for good contact. I see no drop in the charging circuit tested at the alternator and at the battery.
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By 2721955meteor - 8 Years Ago
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you sead the battery is from a rv,is it the house battery ,if so it should be a deep cycle that being the case that is the first thing to change. deep cycle batterys ar intended for long periods of low draw,not recomended for car or truck. a deep cycle takes longer to charge and after starting the truck for tests alternator sences low charge and load the engine at idea..
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By Talkwrench - 8 Years Ago
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Your Pertronix unit wont like low voltage.. If your electrical system is sad then you turn your lights on lowering the voltage more ... well ?
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By paul2748 - 8 Years Ago
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Check the output of the charging system by using a multi-meter or similar and checking voltage output at the battery. Around 1500-2000 rpm's an alternator should be putting out 13.7 to 14.5 volts. At regular idle it may be a little lower.
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By ianmatt - 8 Years Ago
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I tried checking all grounds and ran a new ground from intake to cab just to have extra. seemed to help a tad. The battery has a cold crank of 550. Thats low right? I drove the truck to work today so i can go grab a pic of the battery if you guys want.
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By charliemccraney - 8 Years Ago
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think you can fit a battery with more cca. However, if the engine starts, then the battery is not a problem in that respect. I wouldn't spend money on a battery simply because of that.
If the grounds check out okay, make sure all of the connections are good, no corrosion frayed wires, etc. Once that is verified, start your troubleshooting of the battery and charging system.
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By Talkwrench - 8 Years Ago
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550 CCA should be fine
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By 2721955meteor - 8 Years Ago
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ianmatt (11/23/2016)
I tried checking all grounds and ran a new ground from intake to cab just to have extra. seemed to help a tad. The battery has a cold crank of 550. Thats low right? I drove the truck to work today so i can go grab a pic of the battery if you guys want.
not so charley,a deep cycle will start the engine but will show low charg after heavy load, as deep cycle ar desighned to run a rv furnace all night etc,not desighned for a car or truck. example if you try and charge a deep with a regular car battery the alt will sence full charge befor the deep cycle is charged and cut out. the chart to min.. another example in real cold weather deep cycle will fail to turn the engine fast enough to started amp -25 etc.
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