Car is a '98 Z28, A4, with 13,400 miles. Car has stock pulleys, and nothing more than very minor bolt-ons (catback/air lid).

This one is really odd. I noticed Saturday that my "check gages" light was flickering, but only when I would accelerate. I didn’t see anything wrong with any of the gages at first, but later I noticed that the volt meter would dip into the red zone when the “check gages” light would flicker. I a-tapped the car to make sure that the dash cluster was reading correctly, and it is. I put as much load on the system as possible (every accessory), and the charging system did fine, 13.0-13.2v under FULL accessory load and 13.6v under normal/light load (those readings were from a-tap). A check at the battery (using a multimeter) revealed 13.9-14.1v at fully warm idle (14.5v+ when cold) with normal/light load. When the ignition is off, the battery shows 12.6-12.7v.

I continued scanning the car while driving to try to duplicate the condition, and I did. Sure enough, a-tap shows the voltage dropping to 11.7-12.0v under acceleration *intermittently*, and that’s when the check gages light flickers.

I figured that it must be the alternator failing under engine load, because frankly I don’t know what else could cause this. It’s not a failing tensioner or slipping belt because the power steering feels fine when all this is going on. Anyway, the belt is new with about 1.5K miles on it.

The battery is new as well (one year old) and holds a charge great. The car sits a lot, and the battery is always fully charged when I go to start it. It’s never weak, and cranks 100% strong always.

So, I figured the only “old” part in the system was the alternator so I replaced it with a GM unit directly from the dealer (I’ve been through plenty of bad rebuilds from Pep Boys & Autozone in the past, never again). This was clearly not the issue. The new alternator gives all the exact same positive readings as the old one, and the intermittent problem is still the same. IMO, this is not caused by a bad rebuild, because both the stock and replacement unit are showing this exact same condition, which isn't even a common failure condition for an alternator in the first place.

Charging is PERFECT at idle even under heavy accessory load, and charging is still perfect when free revving the motor. But when I start to accelerate in gear, as the rpms go up, the voltage goes down all the way to the 11v range. When the car upshifts and the rpms drop, charging improves, but as soon as rpm starts to build again, charging falls off. Keep in mind, this is an *intermittent issue*. I've checked and rechecked all the wiring relating to the battery, alternator, starter, and associated grounds, and nothing is loose or damaged or corroded. All the fuses in the dash and the engine bay seem fine. I am getting no DTCs or pending DTCs of any kind. The car runs perfect other than this issue.

So what the hell is causing this? Any ideas? This is the exact opposite of how a standard charging issue normally would be. Who's ever heard of charging being reduced by an increase in rpm? Usually the problem is at idle and gets better when you drive.

Any ideas would be great. I know these cars very well, but I'm stumped by this issue. Thanks.

 

Might try this guys solution
https://ls1tech.com/forums/general-maintenance-repairs/495521-check-guages-flashing-driving-me-nutz.html

 

i had a blazer once that i bought used, when i accelerated sometimes the dash lighs would flicker (not just the check gauges light so this may be different) I looked under the dash and the ground wire, that came from th edashboard was affixed to the sheetmetal inder the drivers side kick panel by a 12mm bolt. I tightened this bolt and all fickering was gone. But that link says it was a plug wire issue, that sounds like a possibility as well.

 

Thanks for the link, but I think this guy's issue is different. Looks like his problem was only at/near idle and goes away when driving. Mine is the oppsite, being fine at idle and only surfacing while driving. Also he mentioned a hesitation, which I do not have. Actually my car is running great other than this issue.

I did think about a possibile plug wire arcing causing a sudden voltage drain, but the wires all look good and are all seated tightly. I feel no miss or loss of power either, nor can I hear the common "crackle" of an arcing wire. They are the stock '98 wires, but with only 13K miles they are basically new still. Either way, I do have a brand new set of stock wires in the box that I could toss on just to see if it makes a difference, but somehow I'm thinking I won't be lucky enough for the fix to be so simple.

Thanks for the reply.

I checked all the grounds I could in the engine bay but never thought to check any interior grounds. I can't say that I've noticed any lights flickering, but so far the issue has only happened in the daylight so who knows. But considering the issue seems to effect the whole eletrical system it's probably not just a dash ground. I could check that just to be sure though.


Any additional replies are more than welcome, I'll take any ideas I can get.

 

Bump.....

 

Battery hold-down, letting it roll back & short to the
wheelhousing sheet metal?

Might chase down all of the block-batt, block-sheet
metal straps and be sure nothing got loose or crusty.
8-9 years old, may just want a wire brush & tighten.

 

Check the ground on the back of the left cylinder head...this is where the PCM gets its ground. Make sure they are clean and tight.

 

Ok, as of now it seems that the issue is gone, but I’m not sure if it’s something I did to fix it, or just the intermittent nature of the problem.

I tried everything mentioned in this thread short of replacing the plug wires because they are stock with low miles and all seem fine from what I can tell. In addition, my issue was different than the one mentioned where plug wires were the problem. If my problem returns, I’ll consider trying that next but I still doubt it’ll help.

Anyway, I checked the battery hold down tray and it was tight and secure. I checked every ground wire I could find (including the one on the back of the drivers side head) and all seemed clean and tight. Only one that concerned me was the ground wire that runs from the drivers side of the block to the frame; the one that is not insulated (woven copper). I noticed that the wire was resting on the alternator case and was very close to the red exciter/field wire plug on the back of the alternator. My only though was that this ground wire might be tightening against the alternator when the motor torques under load and either discharging the alternator somehow or drawing power from the exciter plug. So I moved the wire some and added more electrical tape where it emerges from the plastic conduit and zip-tied it off the body of the alternator

The exciter wire itself seems to be plugged in snug and the wire is not damaged nor does it seem to be loose or separating from the weatherpack. I’ve tried jiggling that wire many times and can’t duplicate the condition so at this point I have to assume that the red wire is not the problem.

So for now, frankly I don’t know if it’s fixed or not. Guess I’ll just have to wait and see if it does it again.

 

Not to dredge up an old thread, but I'm having the same problem. Check Gages light will flash under load at high rpm. It won't do it when revved without a load. I've check coolant and oil levels. I also changed the belts (due, stock with 84k miles). I noticed the ground strap going to the frame rail above the alternator seemed to be loose and touching the case. Gotta check that out and hopefully fix my problem as well.

 

Here is my update, just as a point of reference.

It’s been over a month now and the problem has never returned after driving the car several times. My only guess it that moving that ground wire must have been the solution. What I can’t understand is why it suddenly became a problem after all those years, I guess the wire must have shifted slightly.

I’m still confused on how the wire was able to discharge/disrupt the alternator, but somehow it must’ve. I didn’t even tighten the wire, just moved it away from the alternator case and that seemed to fix the issue.

The whole thing was really odd if you ask me. Hopefully you’ll be able to fix yours using the same method. Give us an update after you try it; the more info and results the better chance that this thread can help others in the future.

 

That fixed my problem. Upon investigation, I found that the power cable that comes from the battery and goes to the power point near the fuses was actually tight against the ground strap. It had worn a shiny spot on the ground strap. In doing so, it was also drawing tight against the alternator case. I unbolted the ground strap and wire where they bolt to the "frame" and rerouted the ground strap behind a power steering hose and wiring harness bundle. There is now slack so the ground strap isn't chaffing against anything and routing it around the power steering hose pulled it away from the alternator case. 10 full throttle, 6000 rpm blasts later and the problem is no where in sight. I took some pictures of the offending strap, but they didn't turn out very well. This picture is after I had already rerouted the strap. I outlined it in black for clarity. I figure one of two things happened:
1) The ground strap touching the case provided a shorter ground path for the voltage output leading the circuit to read an instantaneous "large" voltage drop causing the check gages light to flicker.
2) The ground strap being so close to the power wire coming from the battery induced a current showing a false high voltage drop triggering the light.

I lean towards the former myself. Hope this helps someone else in the future.