electrical power "dip"

[tonkater]

I've noticed a weird symptom on my 02 dmax. Sometimes (not always) when I let up off the accelerator (going say 50 ) I'll notice my lights will dim for a few seconds. I've also noticed it during the day , with heater motor slowing down.
Volt gauge doesn't change any when this happens.

Its acts similar to the diming/slow down when the glow plugs on my 6.2 cycle after start up. But the glow plugs aren't cycling when this happens , since the trucks warm , perhaps been running at least 1/2 hr or more. It will be going to dealer to be checked , but any hints ?

[YZF1R]

This has been mentioned before and I think the verdict was "normal". Mine does this too, but on mine and I believe everyone else's you can see the voltmeter dip.

The general idea is the regulator seems to take a second or two to pick the voltage up when the rpm is suddenly dumped to idle. Mine won't do this above 44mph or so in high gear or the upper minimum limit of a lower gear. If you are going fast enough in any givin gear (before lowest up-shift speed) and let off the throttle to idle, the trans will grab the engine enough to keep the engine from going quickly to idle, and avoiding the voltage dip. Seems the regulator can keep up with decisions as long as it doesn't have to think too fast.

I would not worry about it. Mine has done this since day one with no ill effect.

Perhaps someone else could explain it better than I.

Steve

[SledZep]

Have/had it too. If you watch closely your gauge is probably dropping considerably. Mine was. It took 2 trips but they finally replaced my alternator and now it only happens on the rarest of occassions.

SledZep

[tonkater]

Normal, I don't think so, no other GM product I've ever had did it. It is intermitent , I can be doing 50, 65 , or 20 , take my foot off fuel and it does it. Gauge doesn't drop,which confusses me. (showing around 18 volts the nite I really noticed it.)

[YZF1R]

If it is doing it at what you consider too often (maybe doing it at all is not good), take it to the dealer as SledZep did. There is good reason to believe they will install a new one as was done for him. Take them out in it and make it do the dip, then switch seats and see that they can do it too. Hopefully you'll get a new one. ;)

Steve

On edit: If it were showing 18 volts that doesn't sound right either.

[ 01-23-2003: Message edited by: YZF1R ]</p>

[FisHn2DMax]

Tonkater,

I noticed the same thing right after I took delivery of my truck. It drives me nuts! The dealer and others on this forum seem to think it's just the nature of this beast? Please look up my previous thread and responses on this same issue (listed below). I hope someone can come up with a solution, because it isn't right to see such large voltage fluctuations! I personally think the voltage regulation design in the alternator is very poor and the guage of wiring used is too thin. I believe we're seeing IR drop (voltage drop) in the 12 volt wiring due to thin guage wiring. While it probably won't cause burned up wires, it can't be good long term. Just like the JK Headlight wiring kit solves the thin OEM wiring for the headlights, we could have the same issue with the intake heater,Glow plugs and lights since these pull alot of amps. Our dash voltage guage may not be accurately reflecting the actual battery voltage when there is a high current demand from accessories. I notice large voltage fluctuation when the intake heater cycles and the abnormally long delay before the alternator voltage regulator kicks up the voltage, and the long delay before it kicks the voltage back down after the load is gone. IMHO, it's due to a combination of the thin wiring and the slow reaction of the Alternator voltage regulator. I still believe that GM won't seriously address this problem until enough of us let them know it's not acceptable. Take it to your dealer and complain as I did. However, don't expect an immediate solution from your dealer. In your case, A new Alternator might help, but I doubt it will totally solve the issue?

http://forum.thedieselpage.com/cgi-bin/ultimatebb.cgi?ubb=get_topic&f=3&t=004750&p=

Good Luck smile.gif

[Oongawah]

My 02' Duramax Does it
My 02' Yukon Not as bad
My 95' Camaro does it worse

I'm really messed up, but havin' fun.

[NWDmax]

Mine does it when I let off the throttle or coming to a stop.Noticeable dimming of the headlights and definately registers on the voltage gauge.Personally I think it's normal for these trucks as my buddies 2002 does the same thing. Blake :eek:

[GMC D-Max]

Ditto, ditto, ditto!!

I figured I'd cure it myself by FINALLY adding the second alternator (and maybe replacing the original one with an AD-244, too). Less hassle than taking it to the stealership.

[hoot]

Probably something to do with the injection system. It uses quite a bit of juice. Taking your foot off the accelerator might cause the injection system to do something that requires a "spike" of power.

Just a guess.

[drgracr]

Mine does it also, only in the winter lots of electrical load. This is what I was told by the electrical genius at the dealer where I use to work.

The voltage regulator from what I understand is controlled by the ECM. This is suppose to prevent voltage spikes to the electronic moldules (bad) this is also why it doesn't start charging right away when cold, lots of electrical load. I also found Caddys did the same thing under high load.

Right or wrong, I don't really know :rolleyes:

[Vivayo]

Well, my 6.0 does it too. Did it tonight as I was driving across Andrews AFB. Speed limit on most of the base is 25 MPH (some is 15 and some is as high as 45) and it's a federal offense if they ticket you. You gotta go to federal court in Baltimore if you wanna fight the ticket. They act more like you just heisted a bank than just exceed the limit by 3 or 4 MPH, so everyone stays real close to the limit - even in the 15 MPH areas :confused: After 22 years in the Navy, I've learned that base cops everywhere are bored to tears and just looking for someone to punce on.
As I crested a small ridge (at 25 MPH) and let off the throttle, lights dimmed. I touched the go pedal and they picked back up but this isn't the first time I've seen it.
Charlie

[SledZep]

Getting a new alternator from the dealer (2 visits) has helped mine alot. I would say it is decreased by 90% I can live with it like this, not the way it was before. I think everyone should press for a replacement. Just because all of them do it does not make it right.

[GMC D-Max]

Did they replace it with the same part# (105a), or did they replace it with the AD-244 (130a)?

If I could get my dealer to replace it with the higher output unit, I'd be making an appointment today!

[tonkater]

I'm glad to see many of you don't consider this "normal". I've not had a chance to talk with my dealer about it yet. A couple questions :

did the 130 amp alt help ?

did going dual alt help ?

anybody go aftemarket high output units and have them cure it ?

[SledZep]

Mine was replaced with the regular alternator again. At first I said that the problem had dimished by 90%. That seems to be changing. Now maybe it's 75% better than it was before. I hope it levels out here or I am going back to the dealer again.

[SwampMonster]

WOW! I am soooo glad that I am not the only one who has this problem. It is not isolated to the Dmax trucks. I had the same problem with my 2001 Z-71. I always suspected a bad alternator, but the problem never got bad enough to complain about it until the truck was well out of warranty. When I traded for the Dmax I figured y problems were behind me, only to be disappointed again. From the sounds of things I will be replacing the alternator out of my own pocket. At this point I do not trust the junk that GM seems to be outfitting these trucks with. Thats the downfall of capitalism: lowest bidder always wins.

Thanks for the info guys.

Lata

[ 03-07-2003: Message edited by: SwampMonster ]</p>

[GMC D-Max]

I have to agree that it's probably a sub-standard alternator and/or voltage regulator. I finished putting the second alternator on mine, and I haven't noticed the dip in power since. I'm sold on the idea of dual alts, as it effectively doubles (or more) your output at or near idle speeds, which is where we're all having problems.

[SwampMonster]

I have toyed with the idea of dual alternators. Would you mind sharing some pics of how you accomplished this?

Thanks

[Oongawah]

Time to stir the pot.

If the altenator was to blame for not putting out enough power, then you wouldn't have this symptom. Think about it. What would be the symptom if you didn't have a battery? I think the problem is the battery. I changed it in the Camaro recently, and the problem went away. Cheaper fix too. Take care, Chuck.

[SwampMonster]

Well it seems to me that the alternator does not produce an ample amount of current at idle speeds to keep the electrical system happy. At highway speeds it acts fine (no headlight dimming problems). Once I slow down to make a turn or stop, is where the problem lies. At this point the RPMs of the engine have reduced from highway speed to near idle conditions. The alternator is probably not able to maintain its normal operating charging voltage. With the voltage drop comes an increase in current draw, which may cause the alternator to momentarily 'shut down', thus reducing your operating voltage back to the 12-13 volt range that your batteries supply.

It may be a battery issue, but if I had to bet on it I would lean towards the alternator.

Lata

[GMC D-Max]

Swampmonster,
If you do a search on this site, you will find much valuable information on adding the second alternator, including part#'s, tips and shortcuts.
It's fairly easy to do!

[SledZep]

I believe it is the voltage regulator. When you are going faster the alternator puts out so much power so easily the regulator must keep it from frying the batteries. I believe when we slow down and the RPM's drop quickly the regulator does not let extra current flow quick enough to keep the loghts from dimming.
If it were the alternator not putting out enough we would have dead batteries after a while.
If it was the batteries it would happen everytime we slowed not intermittently.

[Cajun W/Duramax]

I have a cousin that has an alternator & starter shop. I mention the problem about the voltage dropping off to him the other day, he said there is a load limiter built into our alternators. When the rpm's drop off rapidly the load limiter shuts down the alternator for a few seconds & slowly comes back up. This is very obvious when you first start up in the morning, watch your voltage gauge, it will be at about 12v when you start up and it will slowly climb to around 14v. When the alternator drops off your light etc. are running on 12v from the batteries, when alternator is charging your running 14v maybe almost 15v. Two or three volts makes a lot of difference on a 12v bulb.

Do not ever on any of the newer vehicles undo the battery (s) while it is running, as we use to do in the old day's to see if the alternator is putting out. On these modern vehicles when you undo the battery on a running vehicle the voltage from the alternator can go as high as 70-80 volts with no load on it. What do you think your computer(s) will do if you run 70-80 volts through it? How do you like your eggs??? My father in law tried this a couple of years ago, computer cost him $250 from a salvage yard. Anyway a little FYI! tongue.gif

[SledZep]

Cajun, that did not make sense to me (which is not unusual) When you first start your truck there is no dropping off of RPMS. Is there? I believe the lower voltage in the AM is the fuel heater. It was pretty well researched here on this board. I notice that my voltage returns to 14 much slower on very cold mornings than when it did not go below freezing.
My thinking is more along the lines of the regulator/limiter keeping the output of the alternator at an artificially low percentage of max output while RPM's are high. Then not letting the percentage rise fast enough when the RPM's drop.