Charging/Electrical Gremlins.....Any thoughts?!?!

[2kwik4u]

OK I need some help from the resident electrical guru's. I'm a bit stumped. My '03 GMC Yukon has been giving me some fits the last week or three.

The truck has been doing well for 3 years. Voltage gauge is always right at or above 14v. Always. Never moved. Ever. Until about 3 weeks ago on the way to the lake with the family. I notice the gauge is bouncing around between ~11v and ~14v. As I'm parking the truck/trailer after offloading the boat, the truck just dies. The lights in the cabin flickered once or twice, then it died. It started right back up, and I finished parking. When I got back in the truck after a day on the lake, the A/C blower didn't work. Troubleshot that when I got home (after riding home with no A/C for 2hrs), and replaced the resistor. The voltage came right back up to a solid 14v for the next week or so. It's now wavering again, and the truck has died on me twice. It's acting like a bad ground maybe. I popped the hood, and there is corrosion all over the battery, it's at least 3 years old, so I replace it with a brand new DieHard Gold (upgraded from 650CCA to 795CCA while I was at it). I was hoping that maybe a dead cell in the battery was shorting out causing the stalling, as they both happened when I was either braking, or on a wierd angle at the ramp. New battery is in, and it hasn't died since, however the voltage is back to "bouncing" between ~11v and ~14v. Not a consistent bounce, but WAY more movement than I have ever seen in the past. So I think, well the voltage regulator is probably bad in the alternator. It's 7yrs old, and has 140k miles on it. Might as well replace it. Napa has a new 145amp on the shelf for $160, so I go pick that up. ZERO change to the charging condition. Still moving around on the gauge WAY more than I would like it to.

My next step is to throw new cables between the following locations in hopes that I can improve the connections all around, and make it easier for the electrical system to do it's job. Napa has some premade 4ga cables in various lengths for ~$6/ea. Figured I would grab some of those and just add those to the existing system.

Alternator-Battery+
Frame-Battery-
Frame-Engine Block

Can you guys think of anything I'm missing here? Are there any other connections I should be checking/adding? Is there a PCM controlled item that I might need to address?!?! If these new cables don't steady that voltage back up, I'm at a loss for what to do.

 

[Eagle]

Id have that alternator checked. new doesn't mean good.

I would have also guessed bad battery, that s what it was in my case.
Luckily I had carried my DMM with me on vacation, and I was able to confirm a bad battery by seeing voltage was a 10.3 at rest... instead of 12.6

 

[Rivieraracing]

Is your truck idling like normal during the voltage bouncing around or is the idle bouncing around with it? If it is, try cleaning out the throttle body!

 

[2kwik4u]

when the needle is "bouncing" the truck is typically either in a cruise state (like the expressway), or sitting at a stop light with a steady idle at ~500-600rpm or so. It's not a fast "bounce" but more of a steady move from ~11v to ~14v. It's like it think it needs to charge, so it ups the voltage, then it decides it's charged enough and moves back down, then repeats. Sometimes when I get off the expressway when it's been charging ok at ~14v, when I come to a stop, it'll drop to ~11v or so, and then SLOWLY climb back to to just under 14v and hang out there.

Also, it seems to be a engine warm thing. I started it up and drove it about 15mi yesterday morning, with ZERO problems. Stayed there for quite a few hours, when I went to come home, the ambient temps had risen from the mid 70's to the high 80's.....The charging problem was back. Same thing with a trip to the grocery this morning. Temps in the mid 70's and NO problems.

It's really stumping me.

 

[Eagle]

bad voltage regulator in the laternator. failing with heat? might have to test it while it is hot. Or just take it back and say it has a problem, get another.

 

[2kwik4u]

It's funny, the last one did the same thing. Also, this morning on the way in, I noticed that the engine was "surging" a little at idle with the A/C on. I switched off the A/C, the idle came back up to a steady 500-600rpm, and it charged just fine. I'm wondering if this is a sympton of the A/C not working right causing a low idle. Then with the blower on super high, and the radio on, and the headlights on, causing a low/no charge situation.

I still haven't upgraded the cables due to an overly busy weekend, but I did drive it around quite a bit yesterday (50 boat haul to the lake and back), and it charged fine for that entire trip except for the 10 minutes of loading the boat. Turning the A/C off then also helped it return to "normal"......

This is aggravating to say the least!

 

[Thumper8302]

clean the hell out of ur throttle body man.... ur iac motor is throwin a fit and its not letting ur motor compensate for the idle therefore when ur idle drops ur voltage drops..... if its 7 years old with a 140k on the clock im sure its time. hell im runnin 9 yrs olds with 233k on the clock... get u whats called DEEP CREEP... some of the best stuff u can get ur hands on...

 

[2kwik4u]

clean the hell out of ur throttle body man.... ur iac motor is throwin a fit and its not letting ur motor compensate for the idle therefore when ur idle drops ur voltage drops..... if its 7 years old with a 140k on the clock im sure its time. hell im runnin 9 yrs olds with 233k on the clock... get u whats called DEEP CREEP... some of the best stuff u can get ur hands on...

I'll give that a try, but it doesn't explain the voltage drops when cruising.

There almost has to be a loose/failing connection somewhere.

 

[Eagle]

it still sounds like either a failing voltage regulator, or a bad battery, or a bad terminal connection leading a poor charging situation. idle rpm, consumption > amperage out (a/c blower compressor & other electrical devices) = falling voltage problem.

(Or where the Alternator charging wire is tied to the battery wire under the protective cover?)

Also double check the negative 'ground' connection to the block and to the battery.

I'd go look at mine and tell you exactly where they are, but i don;t have an NBS anymore.

 

[2kwik4u]

I concur that it is acting like a voltage regulator problem, but it seems very odd that my 140k 7year old unit was producing the exact same results as the brand new out of the box unit. Leads me to believe that it's something else awry in the cabling somewhere.

I swung by the parts store last night and picked up some pre-made cables. 4ga in 19" (shortest available), 36" and 48". They are pre-terminated with a large eyelet at each end, and were about $6/ea. I also picked up a new battery post "extender". It's really a bolt taht goes through the stock battery connection, and has a longer post with another bolt on the outside to attach additional cables to.

I'm replacing the cables one at a time to see which connection will be the "solution". Last night I installed the 19" cable from the rear of the alternator to the post in the little red box attached to the positive battery cable. Essentially replacing the stock 8ga cable with a much larger 4ga unit. I left the 8ga there just as a backup.

Initial startup on the engine this morning showed ~14.5v on the gauge. A big improvement from the previous day. However after my 15mi commute into the office, it was back down to ~13.5v or so. Just under the 14 mark on the gauge. I kept a pretty close eye on it while driving in. No consistant dipping down at all throughout the drive, with one exception. Once while cruising at 70mph on the expressway, I saw it dip down to ~12v or so, and then come right back up.

I'm going to add the cable between the battery and ground tonight and see if that improves anything. I might go ahead and add the ground to block cable as well. I saw a writeup somewhere this weekend that outlined using one of the bumper attachment bolts as the grounding point (once cleaned and scuffed thoroughly), and then obviously one end heads to the negative battery terminal, and the other end heads to the alternator mounting bolt.

I'll keep everyone posted.