Cbrymer54

I posted a couple months ago about losing power under hard acceleration @ about 4500 rpms. I had it dyno'd which proved that power was dropping off. Well after about 4 visits to the dealership and a month of waiting (b/c they couldn't figure it out either), they finally received a "hint" to what it might be.

The problem was the ALTERNATOR!! Now the first explanation I got from the dealer was that the alternator cables could be running parallel to the pcm cables and creating EMI. However what I was eventually told was that it was the alternator itself. Basically GM never really had a vehicle that has reved up to 7k RPM before, and instead of doing there homework and desinging an alternator made for this type of performance application, they just used the typical one you can find in most GM vehicles. So I'm not sure if the EMI story is still true, that when the engine was reving past 5k or so that the alternator was creating so much current it was causing EMI (Electromagnetic Interferance) with the computer. The shop foreman did tell me that the frequency wave readings from the alternator @ over 4500 rpms was very sparatic and not smooth and consistant at all.

In any case, they replaced the alternator within a couple of hours and now I can finally FEEL all the power I have heard about. It made a world of difference on the top end. Now all I have to do is go find that mustang that eluded me to this problem in the first place

If anyone has any specific questions, let me know and I will do my best to answer.

Thanks.

Blitz_

That's great news. Funny how things work... Enjoy!

allanlaw

Maybe vaguely related to this:

"Some customers may comment of a "Service Charging System", "Service Electrical System" and/or a "Battery Voltage Low" message on the DIC accompanied by DTC P0621 in the PCM. This may be the result of a cut in the stator winding that is caused from a high RPM, usually because the engine hit the rev limiter. The internal fan is flexing and when it does flex, it comes into contact with the winding. A new one may do the same thing if the engine is up against the rev limiter a couple of times."

Dr.Ron

Glad you got it worked out/solved!

Ron

Short-Throw

Thanks for the follow up. Enjoy!

Allan,

Have you ever been on Jeopardy?

trumper Z06

Hhmmm... I never had or heard of this problem with any of the C-5 Z06's !!!

I didn't adjust the rev limiter on either of my C-5's.. but I know of a few guys that moved theirs up.

JDRacing

I suspect it's exactly related to this. I posted that I had this issue as well about 3 months ago, and believe that my fins have been clearanced by running it to redline a few times. However, the first time I took mine to redline, not only did I get the "Service Charging System" message, but the power in the upper range dropped off dramatically (easily felt).

In nosing around LS2edit tables, I note there is a speed limiter, for both normal (205 mph) and "fail" modes (80 mph). I'm guessing that when this fault code appears, it kicks it into fail mode and limits engine performance accordingly. Just a guess, and maybe there are other reasons the fault noted above limits engine performance.

Ranger

Is the speculation that some small number of these alternators have defective internal connections that emit the EMI? Must be the case because the issue is quite rare.

Ranger

vettemaster1

my early production z has been against the rev limiter alot....never missed a beat .....takes a lickin and keeps on tickin

allanlaw

No, but I usually feel like I'm IN Jeopardy. BTW getting the car ready for the track tomorrow and the car won't start - I forgot to leave it on the trickle charger for the last week or two, so leaving the doors open yesterday and today while installing the belts, etc. was enough to drain the battery (it's not dead, just tired enough so the engine won't fire).

VINZVET

So has GM redesigned the alternator or just installing a new one with the same design??
V..

Cbrymer54

I didn't get exact details on the issue but I will request them for reference. I know that when I first went to the dealership with the problem, nobody had heard about this and there was no other reports, to the dealerships, with the same symptoms. However, about 2 months after the initial visit, there were apparently 5 other cases reported and I guess another dealer did some better troubleshooting and figured it to be the alternator. So far, in all the cases, the alternator was replaced and it fixed the problem immediatley. That is all I know so far.

Zred06

Did they replace your alternator with the same part number/alternator type?

outnumbered

[QUOTE=Cbrymer54;1559861682]

Basically GM never really had a vehicle that has reved up to 7k RPM before, and instead of doing there homework and desinging an alternator made for this type of performance application, they just used the typical one you can find in most GM vehicles.




The ZR1 surely did. I think if they used the standard alternator, they must have assumed that it would take a little more.

Glad you got it corrected.

OregonC6

Exactly, unless they have a 'new' improved alternator that can won't jumble the electronics at high rpm OR they just put the same thing in and crossed their fingers that it might behave differently?

9C1

Going back even farther than the ZR1 -- the red line on the 1970-1972 LT1 (Gen I engine architecture) was 7K, and the alternator functioned fine at those speeds. No rev limiter in those days either. Valve float was the limiting factor.

I think Chevrolet has had enough experience with engines that will rev to 7K-- some of the current engineers may be too young to have been involved in those days, but that is another story. Maybe they slept through that part of class, or more likely the bean counters won another round.
Terry

teds427

Look at the pulley diameter of the old alternators and you can see why the could take the 7K shifts.

5abivt

Diel had a similar issue revving his 388ci LT4 to 8100 rpms. An underdrive ATI balancer and extra underdrive pulley on the alternator fixed this up nicely, not to mention free up 22 rwhp on a mustang dyno

kp@hp

Two weeks ago I had a brand new 07 with the same issue, at 5k rpm and above there was a audible spark type noise that the knock sensors were picking up and the pcm would pull up to 12 degrees of timming, After checking pretty much everything I borrowed a Alt from another z and the problem went away. The internal fan would flex just enough to contact the stator and the vibrations would transmit through the alt bracket into block and be pick up as spark knock..
www.hpperformancecorvettes.com

Cbrymer54

There you go. Are more detailed description of what the "dealer techs" were trying to explain to me.

My only question is, is this something that typically wouldn't throw a code?? My service engine light never came on once.