1993 k1500 idle issue

[rangejunkie]

Ok guys, I got somethin funny going on with my charging system..... I think. Truck is a 1993 K1500 with 5.7L. Problem is when i have the a/c on high amd recirculate, lights on (dim or bright doesnt matter) the voltage on the truck drops. Tested alternator, tested at local parts store said alternator was ok. Until tested when truck was in gear, then said regulator failed. Just replaced with new alternator. At idle speeds, my scan tool says it's sitting at 685 to 700 rpms. All voltage with all accessories and lights running is good 14.5v. As soon as I put it in gear (reverse or drive) rpms drop i guess due to aditional load. Except voltage drops unless I turn one of the following off: lights, recirculation, or fan off of hi. Once I do that voltage returns close to 14v. This all happens while sitting still in gear. Driving operates fine at 14v. At idle in gear it has dropped as low as 12.4v. I have tested my ground wires with power probe and get good continuity indications. Did clean battery to block and battery to body grounds. On my alternator wire i do get 3.4 k ohms, i believe this would be a high reading i did parallel a jumper cable with it and no nchange as far as voltage drop. I'm starting to lean towards replacing the positive battery cable since it is original and showed some corrosion in the molded plastic before i cleaned everything. Imalso starting to wonder if it might be a TPS or IAC issue, should there be compensation with engine rpm when accessories are turned on while in gear. No check engine lights or codes. Battery was tested as well and showed to be good too. If I can get correct voltage readings or know what to look for on my scan tool I could verify the TPS and IAC are working. My scan tool is a snap on red brick MT2500. Don't really want to load a parts cannon. Any help is appreciated.

 

[Nad_Yvalhosert]

The main battery cable ONLY feeds the starter during starting.
The smaller wire, with the fusable link and the one off the alternator (that goes to the powder distribution block of the firewall) are the ones you want to focus on. Those are the ones that power the accessories, ECM, etc.
Remove, replace with a thicker one, that would be a lower numerical gauge number. Bear in mind the OE gauges are notoriously imprecise. Don't rely on them to aid your diagnosis, test your voltage directly from the alternator stud.

Also, continuity tests are inconclusive. All your meter needs is 1 unbroken strand in a 100 strand wire and it says continuity is good, but it obviously can't transmit the full amperage load...

 

[Schurkey]

Failing battery? Won't take (or hold) a charge?

The battery/alternator/regulator/starter and the wires that connect them are a "power team". Failure in any one of them leads to failure in others; symptoms of one may be the result of failure in another.

Test--verify EVERY part of the power team.