Voltage issues

iamtherealJayy · Sep 19, 2022

It’s me with yet another problem,
1978 Chevrolet K10 bonanza with a 350/sm465/np205.
Just got done reshimming the starter for the 8th time and truck fired right up this morning and fired up again leaving work but I filled up with fuel and it’s a slow slow crank but after a few seconds it’ll slightly speed up and few more it’ll speed up little more and fire once it’s turning over fast enough. I then went home and ate lunch and truck cranked slow again but started after a few seconds. As I crossed the intersection my tach and radio died(only lights on in the truck) and I noticed my voltage gauge was pegged to the right. I immediately pulled over and checked it with a multimeter and it showed 16-17.2 Volts constantly. I sat there for probably 15 minutes to let everythint cool since the ground wire was warm etc then drove home since i was only about a mile and a half down the road. The battery is probably 4-5 years old, alternator I have no idea on age I haven’t replaced it. But my question is, in 78 was it an internal regulator or do I have some alternate regulator somewhere? It’s a 2 wire alternator as far as I can tell with a little plug going into the side. I can get photos if requested but I tried to explain as best as I could.

Bextreme04 · Sep 19, 2022

iamtherealJayy said:
It’s me with yet another problem,
1978 Chevrolet K10 bonanza with a 350/sm465/np205.
Just got done reshimming the starter for the 8th time and truck fired right up this morning and fired up again leaving work but I filled up with fuel and it’s a slow slow crank but after a few seconds it’ll slightly speed up and few more it’ll speed up little more and fire once it’s turning over fast enough. I then went home and ate lunch and truck cranked slow again but started after a few seconds. As I crossed the intersection my tach and radio died(only lights on in the truck) and I noticed my voltage gauge was pegged to the right. I immediately pulled over and checked it with a multimeter and it showed 16-17.2 Volts constantly. I sat there for probably 15 minutes to let everythint cool since the ground wire was warm etc then drove home since i was only about a mile and a half down the road. The battery is probably 4-5 years old, alternator I have no idea on age I haven’t replaced it. But my question is, in 78 was it an internal regulator or do I have some alternate regulator somewhere? It’s a 2 wire alternator as far as I can tell with a little plug going into the side. I can get photos if requested but I tried to explain as best as I could.

All squarebodies have an internal regulator in the alternator. I'd take both the battery and alternator in for a load test at your local parts store. Replace as necessary. They have the tools at the store to properly test both of them.

AuroraGirl · Sep 19, 2022

Bextreme04 said:
All squarebodies have an internal regulator in the alternator. I'd take both the battery and alternator in for a load test at your local parts store. Replace as necessary. They have the tools at the store to properly test both of them.

Does the 10si run the sense wire as standard on the wiring plug? To the junction?

Bextreme04 · Sep 19, 2022

AuroraGirl said:
Does the 10si run the sense wire as standard on the wiring plug? To the junction?

yes

iamtherealJayy · Sep 19, 2022

I can replace both of them without an issue they’re both old. But if that doesn’t resolve my issue… where else could it be? My 76 won’t crank after it’s been warmed up. It acts like a dead battery and it’s got a brand new alternator with maybe 3 miles on it(yard driving haven’t insured it yet although it is running way better now) and it has an almost new looking battery. What cca should a 350 need? My 87 has like 850 with the best battery served at my local Walmart lol. And the 76 only has like 650. Usually they all crank fine but out of all three I’m having somewhat serious issues.

iamtherealJayy · Sep 19, 2022

I think part of the slow crank on the 78 is also due to heat I just cranked it and it cranked faster than earlier at lunch. It cranked about two rotations before it fired up. I added a new 8 gauge ground directly to frame trying to help. Any other ideas? I redid the ground at the alternator bracket aswell. Electrical isn’t my specialty, I’ve redone majority of the wiring in this truck from the rigging that it was when I got it.

SquareRoot · Sep 19, 2022

Do you have headers? If so, it could be a heat soaking issue. More likely you have a bad ground somewhere. Unbolt and retighten all the ground points including the ground straps from the engine block to the frame. If your starter is really old the solenoid is probably worn out. It will change speed when hot because of expansion and more drag.

iamtherealJayy · Sep 19, 2022

Negative, stock exhaust manifolds on all three of my trucks. I redid the grounds on the 78, where is the ground from block to frame? I redid the alternator bracket to battery and added a battery to frame 8ga wire.

iamtherealJayy · Sep 19, 2022

Also, starter on the 78 is new I broke the nose cone on the previous starter. Maybe a year old. Battery is maybe 5 or so it was out of my old truck before I got hit by a gravel truck.

iamtherealJayy · Sep 19, 2022

You must be registered for see images attach

Timing is around here I bought a new timing light

SquareRoot · Sep 19, 2022

Normally there are ground straps (like braided steel) from the back of the heads to the cab. Since the cab sits on rubber bushings it's how everything inside the cab gets to ground and back to the battery.

Also, make sure you're timing isn't too far advanced at idle (w/o vacuum). Hot engines struggle to start if the timing is off in the advanced direction. And further make sure the balancer hasn't dry rotted and the outer ring slipped. If so, you need to find the true top dead center, Mark it and then set the timing. Those old dampers go the same route as the rubber engine mounts. Wink wink ,

iamtherealJayy · Sep 19, 2022

I don’t understand how the timing could all of a sudden be too advanced, I slightly regarded it and sent a photo of where it’s at. I can’t read the tab or I’d say degrees.

iamtherealJayy · Sep 19, 2022

According to my research the timing appears to be 4-6° btdc which seems little lesser than “too advanced”
Edit: timing was checked at 650 idle with vacuum advance on full manifold vacuum @ 20 inhg and battery unhooked running off alternator at 16v.

iamtherealJayy · Sep 19, 2022

Just started the 76, sat about a half hour after not wanting to turn over and it fired right up, it’s voltage gauge showed little under the straight up mark at idle and showed little above off idle.

iamtherealJayy · Sep 19, 2022

Replaced alternator with the used one I took out of the 76, it’s charging perfect currently running at 13.7-14.4(headlight on at idle) but shut it off and it barely cranks again. I redid the positive battery cable end, the ground from passenger cylinder head to firewall, added a ground from frame to battery. I’m all out of ideas, guess going to go buy a new battery tomorrow which kinda sucks honestly since the battery tray is just angle iron wedged in there…

Voltage issues

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