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Changed My Alternator, Back Fired, Now Won't Start

B

Bohemian

Guest
my alternator was not charging enough so i ordered up a new 140amp made in usa powermaster from jegs.

installed it, started up fine, charging what I expected. I let it idle for 20-30 minutes, no problems.
Shut it off for a few hours, started it up to take it up to corner to get some gas, a mile away...

partway there is starts backfiring and the charging gauge is pegged, neither have happened before...

then it stopped as quick as it started and resumed as soon as i pulled in front of gas pumps...

I shut it off, put gas in it and now the dam thing won't start at all, I got bupkis, no power, nothing...

currently waiting for a tow truck cause i don't see anything obvious and its hot as f..... outside right now...

hoping someone has some suggestions...

its a 82 k5 blazer with a 350 sbc, turbo 400 tranny.

never came with a computer this year afaik...

pretty basic sbc with a gm hei, edelbrock tvsii automatic choke carb, also pretty new, as well as a new optima battery, new powermaster starter.

everything was working fine till this crapola.

thanks in advance.
 
Don’t know if this would cause any backfiring issue, but did you change the positive wire from the alternator to battery to a larger gauge to handle the increased amperage? May have damaged that wire with excessive current and the heat generated by it.
Also, what’s the voltage read at the battery now when you try cranking it?
 
Sounds like a hot wire got pinched in the alt change over, and now it is grounded to the engine. Check to make sure the alt hot terminal is not touching the engine somewhere. If the allt pulley, or alt itself is a different size then the hot terminal could be laid up against something with the new belt tightening position.
 
1-ton said:
Sounds like a hot wire got pinched in the alt change over, and now it is grounded to the engine. Check to make sure the alt hot terminal is not touching the engine somewhere. If the allt pulley, or alt itself is a different size then the hot terminal could be laid up against something with the new belt tightening position.
Click to expand...

i agree that is what it sounds like but the hot wire to the post on the back of alternator is wide open, nothing anywhere near it.

battery still tests good but i have no power, nothing thats driven off the ignition switch being on works...

don't see any obvious cooked wires either at the moment.

guess i'll start checking fuses, Continuity next.
 
Gonna agree on the fusible link. The big question is what shorted, and where...
 
When you say the charging gauge was pegged, what charging gauge do you have? Voltmeter, or ammeter?
If its an ammeter, then something probably shorted. But, if its a voltmeter, and it pegged, then the voltage regulator in the alternator failed and let full voltage into the system.
Could be as much as a hundred volts. Not sure what an alternator will put out with the regulator shorted and putting full voltage to the rotor. But probably in the 30 volt range.
That much overvoltage would cause excessive current flow pretty much everywhere, and hopefully caused the fusable link to burn out before it did too much damage.
I would remove the main power wire from the alternator and tape it up so it won't short out. Then check the fusable link and replace it if bad.
If the truck cranks then, I'd take the alternator somewhere and have the output voltage checked.
 
Out of curiosity, how long ago and why did you replace the battery and starter? Have you been having an issue that you’re tossing parts at?
 
I've seen marginal fusible links fry after a new alternator was installed,the battery is often low on charge due to the defective one and as soon as a new one is installed it starts charging to maximum output,then the fusible link fails..your supposed to have the battery fully charged up first..but if the link(s) were already half smoked from some previous incident ,they may fail anyways..

A GM alternator (and most others) can & will put out over 130 volts unregulated,and Fordum is correct,that unlimited voltage can fry a lot of things,especially sensitive electronics in computers and sensors--this is how they make them into weldernators ,you "full field" the alternator's field coils with 12V....and kits used to be sold that consisted of a outlet box ,an outlet and two toggle switches,by wiring it into the existing wiring,you could get 110V DC at the flip of a switch and run many tools with AC/DC motors, and lights..
 
I don't drive the truck much, mostly for hunting, but the battery & starter were replaced at different times, over the last 2-3 years when they failed and they were confirmed bad before being replaced...

when the factory battery gauge started showing below what it is normally I took it to two different parts stores and had the battery and alternator checked, they both said alternator was a little weak, but within range, not wanting to be left stranded & having future plans for more lighting I looked for a good made in USA new, not rebuilt one from jegs as I previously mentioned...

I put new battery cables on it about the same time I did battery or starter...

The fusable link suggestions led me to a smoked wire going into the junction terminal on the firewall...

it looks like a po did one of those two into one splices and the one side of that union is what baked, the splice looks pretty professional but the logic behind it does not look sound...
As suggested, the increased amperage
probably found the already overloaded wire...

I've not had issues with it previously, so it did not jump out at me before...

So now I'm looking at the bunch of wires running from the firewall, to starter, alternator, etc, they're tucked out of sight beteeen the firewall and bellhousing wrapped in dryed up, cracked plastic conduit, so I have some fishing and clean up to do I suppose....

As suggested I will get the alternator tested once i get the jinky wiring cleaned up.
 
If the wiring harness is "original" the wires with the fusible links are routed thru a metal conduit that is bolted to a bell housing bolt,the links are usually up inside the conduit or just below it near the starter solenoid,where they connect to the stud on it to get power from the positive battery cable..that metal conduit and the wires gets very hot from being so close to the exhaust manifold,this often bakes the wires inside the conduit,and the insulation gets charred and comes off,shorts to ground,and burns up the fusible links..

On my own trucks ,after having issues with this setup I consider rather hokey,I routed the wires in the tube directly to the battery positive terminal,they may need to be lengthened to reach..leave the fusible links intact or replace them,don't "delete" them..they must be there to protect the rest of the wiring,or everything would burn if any ever shorted out to ground..
GM used to run the wires this way on the trucks before 1973 and didn't have as many issues as the later ones with the conduit pipe did..

After doing that,you now only have one purple "crank" wire at the solenoid,and the battery cable at the solenoid..those two can usually be protected from heat with that spiral plastic tubing stuff well enough to not have any more issues...
I noticed my trucks cranked over much stronger once I moved those wires (and or replaced any burned ones,and the fusible links)...check the positive cable itself well for any spots where it might have rubbed against the frame,engine,etc,it may have a spot that touched ground at one time and may touch again when you drive over a bump,etc..
 
besides my hidden jinky wiring failures, looks like I needed a 6 gauge alternator wire kit for that 140 amp alternator I bought, jegs site did not indicate it was needed or not, it just said the 12si alternator would fit my vehicle, my depth of electrical knowledge is limited, so this got by me... smh

Ultra High Amp Alternator Kit:
https://www.painlessperformance.com/wc/30700
 
So next related issue is can anyone Recommend a good "Made In USA" or Made In Germany Non-Insulated Ring Terminal Crimping Tool for 6 AWG ?

I was having no luck with google, the prices are all over the place, so I emailed painless and asked which style and brand they Recommended for the hi amp wiring kit for the 6 awg non insulated ring terminals and they Recommended the IWISS HX-50BI Cable Lug Crimping tool which does 0-8 AWG.

They sent me a direct link to it on Amazon & while it's made in China it looked like good quality & had some good reviews, and it was only like 25 bucks and tired of having the k5 sit I bought it...

What a POS ! I should have waited, I should have known better than to buy Made in China Crapola!

It makes the most butt ugly crimps you ever saw...
I did some more googling and found some youtube videos showing the same thing, so it's not me...

I'm going to boat anchor it...

No more asian crapola for me.

IF anyone has some Made in USA or Made In Germany Recommendations I'd appreciate it.

thanks in advance.
 
I bought one of those hammer type China crimper...mounted it solid and
used a dead blow hammer for setting the lug. Then soldered the lug to the cable and used heat shrink.... they turned out great!

I think the trick is to mount the crimper solid and use a dead blow, so you don't get a rebound and a poor crimp... :dunno:

BTW....I used copper lugs with 3/8 hole
and 2-0 welding cable...
 
wasted wages said:
I bought one of those hammer type China crimper...mounted it solid and
used a dead blow hammer for setting the lug. Then soldered the lug to the cable and used heat shrink.... they turned out great!

I think the trick is to mount the crimper solid and use a dead blow, so you don't get a rebound and a poor crimp... :dunno:

BTW....I used copper lugs with 3/8 hole
and 2-0 welding cable...
Click to expand...
I use a hydraulic press with the hammer type crimper. I noticed if I was hammering on anything that wasn't stone solid (like a bench), the crimp wasn't as good.
 
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