Just purchased a LUMP as a project: 1983 with an old 1980 SBC 350 and T350 transmission.

Car runs and drives but I'm experiencing the following startup issue (just replaced the battery two days ago). Car cranks, starts, then dies if I don't give it a little gas. Upon starting, the voltmeter gauge reads at the bottom of the "normal" range (I'm guessing around 10 but haven't tested yet). The battery light turns on as well.

Then after about a minute of giving it steady throttle (not hard revving, just holding it at about 1,000 rpms), I can take my foot of the throttle and it idles okay. The battery light also turns off after about a minute, the and voltmeter gauge rises to a normal level (about 13).

The fact that it's charging leads me to believe the alternator is fine. I know the battery is fine as well, so now I wonder if something is drawing power from the battery while the vehicle is off, though I can't spot anything visually like interior/exterior lights.

I've also had the "lightning bolt" light turn on, albeit sporadically (though usually not while driving after a minute or two).

Any ideas?

Thanks, looking forward to being a part of the group!

- Anderson, Houston TX

 

I just went through similar issues with my car (although it still has the V12). I fitted a different alternator in a different location as part of the summer work. Unfortunately the new alternator had too big a pulley and wasn't spinning fast enough to charge at idle. Fitting a smaller pulley fixed things and it idles on the bottom of 13 now. I did noticed before I changed the pulley that if I rev the engine to 1500 or so it would bring the charge level up, and it would stay there after I took my foot off the gas, but only for a minute or so. Then it would fall back down.

I think if you had a parasitic drain you'd have trouble starting the car, as something would be using power when the engine is off. Check the voltage between the battery terminals with the car off and with it running. Should be 14/14.5V when running I think. Anything under 11.5V and it won't be able to turn the V12 over. I have no idea how much power it takes to turn over a V8.

The cranks, starts, dies symptoms sound like you have a fueling problem, maybe the choke? But not an engine I'm familiar with so...

 

Thanks, I hope it’s just an alternator issue; I’d rather not spend a lot of time hunting down a parasitic draw.

For any sbc swap owners who see this: what alternator do you use? I think I read that the Delco CS130 is popular choice.

 

Doesn't sound right. I have a vague recollection from my XJS days that the light stayed on longer than I expected but it shouldn't take that long...although in practice it's probably not of any real consequence. What happens if you rev it higher....say 1500-2000 RPM?

That's an 'over voltage' warning lamp. It should come on when the engine is started and then turn off. It's controlled by the 'voltage unit' behind the dash. Something like a relay....the exact operation of which I've either forgotten or never knew. I'll try to refresh my memory.

Not knowing what, if any, circuit changes were made during the engine conversion might make things a little sticky

Cheers
DD

 

If it were me I wouldn't rely solely on the dash gauge for an accurate voltage reading. Get a DMM or some sort for volt meter and check the battery terminals when running, at the main (at the fire wall) and a know good ground point. Go around the car with the meter and see what readings you get.

I have a digital meter that (it's not the best set up) I have rigged into the ol cigar lighter on the console. When I start the car and the idle is high it will read 14-14.2, 3 ,4 volts. At the same time the dash meter is reading kinda low. When the car warms up and idles down, the digital will go to 13+/- 13.9... all's good and the dash needle doesn't move much, falls some.

The gauges on some of the cars can be quite sporadic.

 

I tested the battery voltage while car is off, while on, and tested for parasitic draw:

Off: 12.8 - 13 V
On: 14 - 14.2
Parasitic Draw: 0 - 30 mA, so basically nothing

When I started it this time, cranked right up, wanted to die, battery light was on for maybe 5-10 seconds then went out. Dash voltmeter read 10 upon first start and pretty quickly rose to about 13.

Could bad grounds cause this? Perhaps a bad fuel filter?

 

Shweet... 14+ is good money...

If you just got the car (sorry I'll have to go back and read more/better) cleaning grounds, like getting a lunch and spend the whole day doing it, is a goooood idea. If you search this site you'll get good info for adding an additional ground to the entire cluster, grounded additionally behind the dash.

Other things that are effecting the idle, the startup when cold etc can all be sorted once we all get more focused on that, another thread, or here if you choose.

Keep at it.

 

MrAndersonGCC,

I wouldn't confuse what the alternator may be doing with what you see on the instrument panel. The instruments are notoriously slow / unreliable due to the cluster grounds etc Don't rely on the instrument cluster readings or get confused by the speed they may take to change. It may have nothing to do with your alternator.

I would be checking the alternator output on a basic level by checking voltage directly at the battery when the car is fired up. If you want a more accurate reading, use an ammeter directly on the alternator output.

Cheers

Paul