'89 Silverado voltage issue

pinkfrogman · 10-04-2006, 02:59 PM

The battery light has started coming on frequently in my truck and i'm wondering if anyone can tell me what's causing it. I would of course assume the alternator first but, the alternator is fairly new. The strange thing is... it only seems to do it if I'm on the throttle. While driving, if the light flashes on, I let off the throttle and the voltmeter jumps right back up to the charge side. This is one of two reasons that have led me to believe it has something to do with the distributor or maybe the coil. The other reason is horsepower....it just don't seem to have what it should under the hood! I think the timing advance and all that stuff is electric.... could that cause it? The coil, distributer cap and rotor, wires, plugs, battery cables, alternator, and starter are new....
Also, there seems to be a funny noise under the hood right about where the distributer would be whenever I rev it up past about 4500 or so....(I'm guessing...there's no tach).... like a squeal or something....
Thanks for any help....I just don't want to start replacing parts that aren't bad....
~pink~ Lloyd

**bruiser** · 10-04-2006, 03:55 PM

If you have an Autozone near you, they can check the battery and alternator. It's free. However, if the battery is marginal, the load test will probably finish it off, and you'll have to buy a new battery.

Spacemonkey6401 · 10-04-2006, 04:40 PM

If you put on new cables, you could have a loose connection or the ground might need to be grounded better, make sure everything's clean and shiny. It's possible the alternator you got is bad, I've had some experiences with Auto Zone as far as alternators new that weren't working right. Not that I don't recommend them, they ALWAYS make it right with me, and having everything in the computer like they do on your vechile has saved me so many times without having my receipt. I brought in an air conditioning pump from six years ago, it was on the computer, and I got the new one for free, needless to say i was pretty amazed.

Also, have the battery tested like the above post stated, that could be it right there.

If it doesn't quite have the horsepower it did before the change of the spark plugs and wires and cap, make sure the rotor is in the same position, I've walked off before thinking i was done, and forgot to tighten down the rotor, only to have it rotate just enough to make it run bad, or not have a plug wire on all the way, or at the worst, I didn't pull this one, but my brother has, put the wires on wrong.

Volt-Schwibe · 10-10-2006, 09:51 PM

when you got the new alternator, did they put your old pulley on it?

it is possible that there was/is a size mismatch, and it is now having problems from high rev.

i'd put a voltmeter on it, and see what it does when the throttle changes. (even though you have one in the dash, a handheld one will be more accurate.)

dressed2thrill · 10-15-2006, 04:37 AM

Check your cables. A lot of people forget to do this, and its a very common mistake. Make sure the voltage cables on your battery are on tight, hitting little pot holes or bumps in the road cause stuff to pop out of place on vehicles.

wheeliedart · 11-09-2006, 01:34 AM

The alt could be bad, these aren't known for reliability, if it has a/c the tensioner could be the culprit. it would make the noise too. try it with the a/c on, see if that makes a difference. the tensioner is mounted on the "push" side of the compressor, causing lots of problems. autozone recently bought out GM's overstock of these units, so You'll get an OEM part from them.
The other thing about these is, the rotor assembly is fixed(no advance) so they are hard on distributer drive gears, furthermore it probably has a roller camshaft, which is made from a much harder material, GM didn't bother to use a hardened drive gear. teeth break off. Not related to Your voltage issue but can leave You on the side of the road, and cause sensor readings to fluxuate, the ECM remembers this, and can pull off advance.
Don't overlook wiring interfering/contacting with Your throttle linkage.

10-04-2006, 02:59 PM	#1 (permalink)
pinkfrogman Registered User Join Date: Oct 2006 Location: Wyoming, USA Posts: 4 OS: xp	'89 Silverado voltage issue The battery light has started coming on frequently in my truck and i'm wondering if anyone can tell me what's causing it. I would of course assume the alternator first but, the alternator is fairly new. The strange thing is... it only seems to do it if I'm on the throttle. While driving, if the light flashes on, I let off the throttle and the voltmeter jumps right back up to the charge side. This is one of two reasons that have led me to believe it has something to do with the distributor or maybe the coil. The other reason is horsepower....it just don't seem to have what it should under the hood! I think the timing advance and all that stuff is electric.... could that cause it? The coil, distributer cap and rotor, wires, plugs, battery cables, alternator, and starter are new.... Also, there seems to be a funny noise under the hood right about where the distributer would be whenever I rev it up past about 4500 or so....(I'm guessing...there's no tach).... like a squeal or something.... Thanks for any help....I just don't want to start replacing parts that aren't bad.... ~pink~ Lloyd

10-04-2006, 04:40 PM	#3 (permalink)
Spacemonkey6401 Registered User Join Date: Jul 2006 Location: KS, US Posts: 47 OS: Win XP	If you put on new cables, you could have a loose connection or the ground might need to be grounded better, make sure everything's clean and shiny. It's possible the alternator you got is bad, I've had some experiences with Auto Zone as far as alternators new that weren't working right. Not that I don't recommend them, they ALWAYS make it right with me, and having everything in the computer like they do on your vechile has saved me so many times without having my receipt. I brought in an air conditioning pump from six years ago, it was on the computer, and I got the new one for free, needless to say i was pretty amazed. Also, have the battery tested like the above post stated, that could be it right there. If it doesn't quite have the horsepower it did before the change of the spark plugs and wires and cap, make sure the rotor is in the same position, I've walked off before thinking i was done, and forgot to tighten down the rotor, only to have it rotate just enough to make it run bad, or not have a plug wire on all the way, or at the worst, I didn't pull this one, but my brother has, put the wires on wrong. Last edited by Spacemonkey6401; 10-04-2006 at 04:52 PM.

10-10-2006, 09:51 PM	#4 (permalink)
Volt-Schwibe Asst. Manager, Automotive Forums; HJT Trainee Join Date: Jan 2003 Location: Behind you, watching you as you type. Posts: 7,372 OS: Click "My System" to view details My System	when you got the new alternator, did they put your old pulley on it? it is possible that there was/is a size mismatch, and it is now having problems from high rev. i'd put a voltmeter on it, and see what it does when the throttle changes. (even though you have one in the dash, a handheld one will be more accurate.) __________________ <signature> TSF is funded by our Admin's pocket, care to help? Power Tip: Subscribe to your thread (Thread Tools) to receive an instant email notification when you get a reply. New Members: Creating a single new thread in the correct section is the best way to assure your thread will receive a reply. </signature>

11-09-2006, 01:34 AM	#6 (permalink)
wheeliedart Registered User Join Date: Feb 2006 Posts: 16 OS: WinXP pro	The alt could be bad, these aren't known for reliability, if it has a/c the tensioner could be the culprit. it would make the noise too. try it with the a/c on, see if that makes a difference. the tensioner is mounted on the "push" side of the compressor, causing lots of problems. autozone recently bought out GM's overstock of these units, so You'll get an OEM part from them. The other thing about these is, the rotor assembly is fixed(no advance) so they are hard on distributer drive gears, furthermore it probably has a roller camshaft, which is made from a much harder material, GM didn't bother to use a hardened drive gear. teeth break off. Not related to Your voltage issue but can leave You on the side of the road, and cause sensor readings to fluxuate, the ECM remembers this, and can pull off advance. Don't overlook wiring interfering/contacting with Your throttle linkage. Last edited by wheeliedart; 11-09-2006 at 01:37 AM.

10-04-2006, 03:55 PM	#2 (permalink)
bruiser TSF Enthusiast Join Date: Jul 2005 Posts: 1,973 OS: xp	If you have an Autozone near you, they can check the battery and alternator. It's free. However, if the battery is marginal, the load test will probably finish it off, and you'll have to buy a new battery.

10-15-2006, 04:37 AM	#5 (permalink)
dressed2thrill Registered User Join Date: Oct 2006 Location: Yorktown, VA Posts: 21 OS: Windows XP	Check your cables. A lot of people forget to do this, and its a very common mistake. Make sure the voltage cables on your battery are on tight, hitting little pot holes or bumps in the road cause stuff to pop out of place on vehicles.