It sounds like you were in a hurry to get back on the road, did they check the old alt to see if it was bad????
Underpowered Alternator? Please help.
Thread Starter
7th Gear
Joined: Dec 2017
Posts: 7
Likes: 0
Underpowered Alternator? Please help.
So here's the dealio. Not a corvette, but I'm having some issues with my 1974 Chevy C10 pickup. It's got a 350ci that's been built up a little. Heavy heads and valve springs, big cam, edelbrock intake and 1406 carb, and HEI distributor...nothing too fancy. Last week I got stuck on the side of the road because my alternator took a dump. Before it died I could barely give it any gas without it sputtering and backfiring. I got a ride to the parts store, bought a cheap alternator, and put it in real fast, and I was able to go home. My lights work fine, but my speedometer and fuel gauge are off, and my radio and heater are very weak. I have decent pick up, but it still cuts out and backfires at high RPMs, and I can't get over about 60mph. The alternator has the correct amps, so could it just be too cheap to power my engine with what it needs? Any advice helps please, and thank you.
Last edited by CheyenneC10_74; Dec 29, 2017 at 02:36 AM.
Thread Starter
7th Gear
Joined: Dec 2017
Posts: 7
Likes: 0
They never checked it. I didn't make it to the store, I had to ditch my truck and get a ride. I changed the alt on the side of the road, and it seemed to run alright until I noticed I couldn't go faster than 60mph.
Le Mans Master
Joined: Apr 2001
Posts: 5,941
Likes: 281
From: Was New Orleans but swam to Baton Rouge LA
Cruise-In IX Veteran
Have you attempted to recharge the battery? When an alternator goes bad the vehicle will still run until it has depelted the battery. Often just changing the alternator will not completely fix the issue because you need to recharge a dead battery. I would suggest putting the battery on a charger overnight and see what happens.
Race Director
Joined: Apr 2007
Posts: 11,152
Likes: 890
From: South Western Ontario
The stock replacement alternator will be fine if you didn't add any big aftermarket electrical loads. The new alternator should be fine if it's working. It must be working assuming you got a boost to get the truck going again.
The speedometer is cable driven so the electrical power wouldn't affect it.
Check the output voltage of the alternator with a meter with the truck idling and no electrical loads on. You should see >14V. Then, try it with the lights on and you should still be >13.5V, You are just guessing at the problem if you don't use a meter.
The wire is not a single strand no matter how many times you post it.
The lights should ALWAYS be bright if the alternator is working correctly and it has enough capacity. You are thinking of a generator or the old externally regulated alternators that could barely keep up at a higher rpm.
The speedometer is cable driven so the electrical power wouldn't affect it.
Check the output voltage of the alternator with a meter with the truck idling and no electrical loads on. You should see >14V. Then, try it with the lights on and you should still be >13.5V, You are just guessing at the problem if you don't use a meter.
The lights should ALWAYS be bright if the alternator is working correctly and it has enough capacity. You are thinking of a generator or the old externally regulated alternators that could barely keep up at a higher rpm.
Team Owner
Joined: Jan 2007
Posts: 53,648
Likes: 878
From: Southern Cal Ca
St. Jude Donor '22
I am confused.
alt dies and it should run off battery!
Lights will dim and car will be act like no power.
You say you swapped alt.
Still had enough bat to start?
Curious description of trouble.
Any update?
alt dies and it should run off battery!
Lights will dim and car will be act like no power.
You say you swapped alt.
Still had enough bat to start?
Curious description of trouble.
Any update?
Thread Starter
7th Gear
Joined: Dec 2017
Posts: 7
Likes: 0
New development...I remember when I was changing the alt, my electric choke wire came off and was resting on my chrome valve cover. I took it off and everything was working fine again. I realized today that my choke isn't opening now. Pretty sure it's just not getting enough air at high RPMs, but why isn't my choke opening now?
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Race Director
Joined: Oct 2008
Posts: 19,233
Likes: 1,672
From: Long Island
A heli takes 12 volts a 1974 coil takes 7.4 to 8 volts.
Run a jumper from the battery to the positive wire on the heli (disconnect the original) and start the truck. If it runs better the problem is that the resistor wire or resister itself is still in the system. To stop the truck pull the jumper.
I would go with a 1 wire alt if I was working on a truck I did not build.
Run a jumper from the battery to the positive wire on the heli (disconnect the original) and start the truck. If it runs better the problem is that the resistor wire or resister itself is still in the system. To stop the truck pull the jumper.
I would go with a 1 wire alt if I was working on a truck I did not build.
Thread Starter
7th Gear
Joined: Dec 2017
Posts: 7
Likes: 0
A heli takes 12 volts a 1974 coil takes 7.4 to 8 volts.
Run a jumper from the battery to the positive wire on the heli (disconnect the original) and start the truck. If it runs better the problem is that the resistor wire or resister itself is still in the system. To stop the truck pull the jumper.
I would go with a 1 wire alt if I was working on a truck I did not build.
Run a jumper from the battery to the positive wire on the heli (disconnect the original) and start the truck. If it runs better the problem is that the resistor wire or resister itself is still in the system. To stop the truck pull the jumper.
I would go with a 1 wire alt if I was working on a truck I did not build.
