I posted this in ls1 tech but wanted to see if anyone here might have experienced this issue.Ive had my swap for many years without charging issues till now.This swap came out from my previous burnt down t/a 2yrs ago but everything seemed to work fine.Recently ive noticed that when im driving..my voltage drops and the car is running off battery power alone and then if i stop and idle it will charge.Im running the bigger truck alt. for more amps.Im using the single red wire from the pcm as the exciter wire and without it unplugged Im getting 9.8v with the car running.When I plug it back into the alt. im getting 13.8v at the battery.When I rev the car past 2000rpm ill gett 11v and dropping the more i rev the motor. Ive been told by a few people my ecm is most likely shot.I replaced the alt and still same problem,my last alt had very bad water damage/corrosion.Ive also replaced the belt hoping it was just belt slip but that didnt fix it.

Im thinking of upgrading my main power wires to the ecm from thin 14ga to 8-10ga wires directly to the battery,same with the main ignition wire wire a bigger relay.Other than that does anyone have advice or seen this type of issue.Its frustrating because its costing me power and Im trying to get ready for track season with alot of dyno time.

 

Less than 11v means the battery is nearly dead, you've been running off it a while

Intermittent charging leading to no charge points to bad alt. Replacements use cheap rectifiers which last almost no time. I went through 4 in two months with my first swap before going with a delco unit from rock auto. A stock unit from a JY is another alternative. 4.3L S10s use the same alt

Upgrading the PCM battery voltage wont help, and you wont find terminals big enough to hold that much cable. Anyways, the current running in/out of the PCM is miniscule, so the 18ga thats there is more than sufficient

 

It doesnt run 11v all the time. It only drops once I start going past 2200 rpm and progressively drops in voltage from 13.8 to 11v or less the longer I stay wot.its just odd the alt charges only at idle or till about 2200 rpm. Ive researched that the exciter wire from the e m should be 10-11v and im only getting 9.8v.

Apparently this has happened to quite a few ppl. But none have posted any solutions they have found. Ill try a new alt thats not a refurb and see if that solves my issue.

Any other issues you seen Pocket for alts.?

 

This can turn into a game of cat and mouse it a hurry. Often it takes a fresh alt and a fresh battery too. I've done the replace alt, 3 months later replace bat, 3 months later replace alt, over and over until I finally listened to the good advice my local wrench friend told me which was

change both at the same time and forget about it.

 

Well that just sucks lol..and to add to my troubles.my starter just left me semi stranded tonight.Looks like ill be adding a new starter or replacing a solenoid to my list of parts,my battery is about 2 months old.I put in a truck size battery..I highly doubt its gone bad lol.The car cranks awesome from the bigger cells...except tonight.

Note to self.I still hate having to push start my car by myself!Thank god a had a slight downhill slope and got the car home.

 

Hmm well these types of electrical gremlins are very hard to diagnose over the net but the starter dying at the same time seems a bit much. You sure the grounds are all good and plentiful?

I did see a guy set his AQ braided oil gauge line on fire once from not having enough grounds. The shielding on the wrap was the only thing completing the circuit.

Is this car your DD?

 

Ok so here is where im at now. I just spent 3 hrs in the driveway on this cold morning.I removed the starter(its 7yrs old when I found my receipt) I checked main cables at the starter which needed to be cleaned.Replaced with a new starter,I opted to replace the alt(again) but with a new unit..not a refurby.Its still a truck alt.Hooked everything back the way it was.Fired up the car and bam 14v at 6000rpm+ no issue.

So here is where i pose the question..keep in mind I do car electrical for a living but always open to learn something new or brainstorm.My grounds are 2-4ga,my power wires are 4ga.Could the 7yr starter have been causing my alt issues being that old tired and contacts were rusting or is it possible the new alt regulators differ from rebuilds and react differently to the ecm signal wire?

Either way im now logging my voltage as I drive for the rest of the week to make sure nothing craps out on me.I also plan of making some splash shields to keep the alt/starter away from as much water as possible.

 

Anything is possible. Ive had some tricky issues with GM starters over the years; Too much heat causing them grief ( old BBC stuff ), Sometimes the terminals spin a little in the solenoid when the cabling is tightened up, and this messes up the internal contacts a bit, causes some erratic behavior ( works today, maybe not tomorrow ) and of course the standard starter issues of dead spot between brushes ( hit with hammer trick ) or bendix gone etc.

All that aside with freshly clean terminals and good grounds you can eliminate the potential wiring/grounding hurdles now. Good plan to log voltage, and just try it out and see if its sorted. It wont take long to realize whats messed up ( if anything now ) once your driving it. As a back up safe guard you could just buy a new starter from CT or PS etc and carry it with you along with the nec tools to do a road side swap just in case. If you get a few weeks trouble free? Return the unused starter

 

Well the starter clearly needed to be replaced.Its lived its life from the original ls1 I had and was the original starter from factory on that ls1.Then when I blew the ls1 and bought my lq4 it has been on there since.It just sucked it all happened at once but it starts alot easier now than it did before with the fresh starter.

So far as I drive the car around and log the voltage on my phone,the lowest it hit was 12.2v and that was from the car hunting idle and dipped pretty low for a second but I was watching when that happened.Other than that if i rev and hold high rpms it hasnt dropped from 13.5v.

The only other slight thing i think was part of the issue is indeed the pulley size.i think the rebuilt units i tried at first had a larger pulley for low rpm/high voltage output but its was being over spun and my belt was not easy to put on(new belt).This new alt seems slightly smaller pulley and the belt wasnt anywhere near a chore to slide on,nor has the new belt stretched out.