Low Idle / Low Voltage? - Team Camaro Tech
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post #1 of 13 (permalink) Old Feb 4th, 03, 08:24 PM Thread Starter
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Im not sure what my problem is here but here goes, when i turn on my headlamps rear derost heat, etc. my voltage drops below the normal level, when i start driving the level rises to normal, but as soon as i stop at a light it drops way down and the lights dim , i ust bought a new battery for the car, the highest CCA's i could get, 750 i think, now i know there are different idle settings, would this problem be caused my a low idle? it does seem to idle kinda low when istop at a light, i think around 500, how would i adjust this idle ? and or do you think i need a new alternator?

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post #2 of 13 (permalink) Old Feb 5th, 03, 02:18 AM
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500 RPM sounds like an OK idle for that car if it's an automatic. If it has a manual trans then I would expect it to idle a bit higher.

It sounds like your alternator is working normally, but might not be quite up to snuff. That car should have at least a 75 amp unit, and could have a 104 amp model if it came with all the bells and whistles. (power everything!)

The alternator is definitely shoveling against the tide at idle with a bunch of accessories on and a little drop in voltage and light dimming is normal. The rear window defogger is the worst culprit. This system can draw upwards of 25A!! (that rear glass is freakin' huge!)

I had an '85 IROC with the 104Amp alternator in it. With all of the accessories operating, I could make that alternator put out 105 amps measured with a current probe at the alternator lead! So, there is a lot of load for the alternator at idle.

Make sure that the voltage at the battery is at least 13.2V at idle with the accessories on. If it's not, I'd suspect that the alternator is getting a bit tired. If it can keep better than 13.2V idling, I wouldn't worry about it.

[This message has been edited by PDQUICK (edited 02-05-2003).]
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post #3 of 13 (permalink) Old Feb 5th, 03, 02:18 AM
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Some alternators require a minimum device shaft speed to "turn on" the field to produce charging. This is what you are seeing when you give it some RPMS and see the lights brighten!

Most of these alternators require 1750 rpm shaft speed and depending on the ratio of your crank to alternator pulley ratios, this may or maynot be happening. Low idle speeds aggrevate this as well.

Usually, a 2.5 to 1 ratio is the norm so a 700rpm idle will turn and keep the alternator working.

You did not give any other details so it's hard to diagnose.

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post #4 of 13 (permalink) Old Feb 5th, 03, 03:24 PM
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I think the guys are right about the alternator. Something in the charging circuit is amiss. Does this car have underdrive pullys on it?

-dnult
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post #5 of 13 (permalink) Old Feb 5th, 03, 05:52 PM Thread Starter
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well i normally see the guage move up around 2000-2500 rpms, and when i 1st start the car in the morning or anytime for that matter i have to rev the engine a bit, and that makes the needle rise to the normal position, so it might not be a bad idea i guess to replace the alternator, the previous owner neglected the car quite a biti ust wanted to be sure my diel was correct 1st..so basically your telling me the alternator is on its way out or is it normal for it to kick into action at around 1700 rpms? it is an automatic, carberated engine

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post #6 of 13 (permalink) Old Feb 5th, 03, 05:53 PM Thread Starter
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<BLOCKQUOTE>quote:</font><HR>Originally posted by dnult:
I think the guys are right about the alternator. Something in the charging circuit is amiss. Does this car have underdrive pullys on it?

the car has regular fan bels on it, no pulleys

-dnult
<HR></BLOCKQUOTE>



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post #7 of 13 (permalink) Old Feb 5th, 03, 06:01 PM
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One 1987 car I have automaticly kicks the rpm up if the A/C goes on since there is a requirement for more power for the fans and clutch I guess. I ended up adjusting the idle speed for with the A/C on since the A/C would be on all the time and I didn't need higher rpms at all the lights. Read your owners manual which is where I found the explanation for rpm going up. Maybe there is a small statement on what rpm the alternator kicks in. Even army hummers generators don't really charge untill a little above regular idle.
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post #8 of 13 (permalink) Old Feb 5th, 03, 06:58 PM Thread Starter
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Yes that is the solenoid on the carb, that advances the idle for the AC, it is controled by the computer, however my carb isnt controlled by the computer, all that was disconnected. and i dont have an owners manual, but id sure like to find one..if anyone knows where i can get a Manual for an 84 lemme know.

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post #9 of 13 (permalink) Old Feb 6th, 03, 12:29 AM
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There is a screw on the driver side of carb used to adjust base idle since originally the engine WAS computer controlled.

Now, it becomes the real adjustment. I'd adjust for 700-800 rpm. The ECU would keep the rpm around here if working.

I'd probably go to Advance Auto, or Advantage Auto and get a Haynes manual from them. Not the best manual, but, better than nothing.

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post #10 of 13 (permalink) Old Feb 6th, 03, 04:04 PM Thread Starter
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ive got the heynes manual for the car , i also have another manual , but i found the heynes to be more informative.
NOW, the idle setting your talking about, does this get set with the car in park? at normal running temp?


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post #11 of 13 (permalink) Old Feb 7th, 03, 12:52 AM
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I would let the car warm up, in park and set it. Then, I would turn on lights, radio and heater, and select Drive to see how much rpm would drop for a load and adjust for a happy medium. That is, if rpm drops to say 600, then adjust idle up to 700, turn off accessories and see what the unloaded rpm registers. If it ends up being around 800-850, then I'd probably leave it. Alittle more advance on initial timing would help also, usually an extra 2-3 degrees.

If the idle solenoid was working and hooked up, every time an accessory turned on, the ECM would compensate by kicking open the throttle alittle.

The way it is suppose to work, set the idle for say, 750rpm, no accesssories turned on, then select A/C, the compressor turns on, and the ECM turns on the idle solenoid to increase throttle to make up for the load, hence, rpm is back up to 750.

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post #12 of 13 (permalink) Old Feb 7th, 03, 01:36 PM Thread Starter
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well i replaced the carb not to long ago, but i was concerned the ECM wasnt working so i bought the rochester carb without the computer controls, my question NOW is this, can i buy the soleniod and other parts that the ECM controls and add them to the carb? because id like to get the thing working the way it should with the ECM, im even seriouslt considering hooking the pollution system back up again and making everything stock.

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post #13 of 13 (permalink) Old Feb 8th, 03, 02:57 AM
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The non-computer carb is completely different. The C3 carb (Computer Command Control!) has and internal duty-cycle mixture control solenoid that cannot be added to your carb.
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