Lights Dim at High Revs
 

Anyone else here notice the lights dimming significantly when RPMs get over 6000?
Headlights, dash lights, everything.

My L’s lights dip once when I lift off the throttle once in the morning. I have never ran my car over 5000 rpm more than a couple times. It has over 200k miles and original timing chains.

Umm,

WHAT ARE YOU DOING?

STOP THAT.

See pic

https://cimg2.ibsrv.net/gimg/www.sat...858cc8c0a7.png


And please STOP THAT.

It is probably worth more stolen than in any condition resulting from the exploration of the rev limiter.

This PSA brought to you by

Derf -- the guy that never sleeps.....

:rolleyes:

Thanks Derf! I appreciate the concern and while I would really like to do better the truth is I'm hard on my vehicles. I'm stuck on the idea that if it breaks it needed rebuilt or replaced anyway.

The issue here though isn't that I'm hitting the rev limiter but that the lights dim as if the alternator stops working above 6000 RPM.
When I'm getting up to speed while trying to merge with traffic I'm usually at full throttle and frequently run it up just short of red-line before upshifting. Consistently the lights dim right as I pass 6000 and just think it's odd. Ive been wondering if it's the belt stretching or the tensioner giving out under the stress.

Could be some slight belt slip on the alt which causes the lights to dim...

its also worth noting that while you CAN rev the engine beyond 6k, at that point it’s well past peak power output... I think the LLO made peak power at 5600? The L24 made it at 5k...

not only can you accelerate faster to shift just above peak power, but it also can slightly lengthen engine life to not go quite so close to redline...

Probably overreaching the design limits of what alternator can put out or how much current the wires can carry. That would be a safety measure so that you cannot overheat the cable or jam high current into the battery.

May also be voltage regulator reaching its limit or overheating, it's converting ac to DC so it might be reduced output with some ripple on it. Maybe the response frequency of the diodes is being reached, again passing ripple.

(No, I do not have any formal grad school training in discrete electrical components. One of the best classes I've ever taken
My major professor taught it. I was his teaching Assistant twice. His colleagues laughed at him in the 90s for not concentrating on ICs.

Who's laughing now????? ;)

It's

As soon as I saw the title of this thread, I thought "belt slipping", Bones. Seems you've already considered that. Try tightening it just a little bit and see if it still happens.

Likely the belt isn’t user tightenable in the S series, I don’t think it has an adjustable alt mount... however I think serpentine belts are like $25-30, right?

I think the price all depends on the length of the belt and how many "ribs" it has. I'd say you're in the ballpark.

I think you might have something there Derf. I remember that racers will commonly change the pulley on an alternator equipped race engine to a larger diameter to reduce the RPMs that the alternator is driven at. They do it mainly to keep the armature from coming apart from the centrifugal force at high RPMs. I won't know until I pull the thing out and disassemble to see if anything has been rubbing inside it but the dimming could be related to that. The belt may also be slipping or it may be bowing out and rubbing on something else but I don't ever hear any belt noise when this happens. Of course just because I don't hear the noise doesn't mean it's not happening.

As many of you have mentioned here the easiest and best way to fix it is to just stop over revving that poor engine. I'm trying, really I am.