Battery/voltage light illuminates under heavy acceleration?

[GMARCH]

Under heavy acceleration at around 4000+ RPM, my battery light illuminates, flashes, and all interior lights dim until the RPMs drop again. Any ideas of what this can be? Is it a battery problem? Alternator problem? Thanks in advance. 2000 5.4l expy.

- also experiencing some trouble starting every now and then. The engine cranks then bogs and stalls, then starts perfectly right after..

- also having the vanishing digital odometer problem..

 

[heymrdj]

Under heavy acceleration at around 4000+ RPM, my battery light illuminates, flashes, and all interior lights dim until the RPMs drop again. Any ideas of what this can be? Is it a battery problem? Alternator problem? Thanks in advance. 2000 5.4l expy.

- also experiencing some trouble starting every now and then. The engine cranks then bogs and stalls, then starts perfectly right after..

- also having the vanishing digital odometer problem..

SOrry no one answered this. If you're still having issues, it's going to be the alternator. Most likely it's DIODE pack has failed or is failing. A fairly common issue. It would be best just to change out the entire alternator. Don't get a Duralast unless you want to be using that lifetime warranty once a year on it.

 

[ELVATO]

I've also heard that low voltage at higher RPMs could be the belt slipping. This could make sense, depending on how many miles he has. Either way, it's a good idea to replace the belt at higher milage. It sucks when you have a broken belt in the middle of the night.

 

[Spooky]

Reviving this because my Expy was doing the same under heavy acceleration. I changed over to a Gatorback belt and that helped until I got a Xcal 3 and E fans. It does it again and I'm wondering if the tensioner needs replacement.......opinions?

 

[GAINMOB]

check alt too..

 

[stamp11127]

When the tensioner spring weakens it will "bounce" while the engine is running. It should stay somewhat steady while running.

 

[MoHawk]

Stop accelerating so hard. I don't think I've ever had my truck over 3k RPM, much less 4k

 

[FordandPolaris]

Stop accelerating so hard. I don't think I've ever had my truck over 3k RPM, much less 4k

1st gen expy's rev much easier than the 2nd gens (I'm assuming you were referring to the original post at the top). I hit 3k every time I leave a stop light through 1st and 2nd gear. 4k is nothing on a hard pass.

On the other hand, I really have to juice it to get my dad's 04 to behave in a similar manner.

 

[KWT2000]

4k is easy to hit even more so when towing, that is where the early modular engines realy come alive,

i would replace the tensioner, and belt and have the alt checked, could also be a bearing issue starting to arise in the alt

 

[1997SCEBFEX]

classic slippage, tensioner, &/or belt combo.
I too switched to the gator-type belt for the supercharger as it would slip; regular serpentine is OEM equiv.

PanHandler.

 

[alaskanexpy]

all my trucks see 5,000+ rpms daily more times then i can possibly count.

your alternator is dying. same thing happened with my excursion. on a 1000 mile road trip making many high speed pass's and running 100mph+ it finally gave out on a pass about 50 miles from home. my belt was fine... but every time i hit 5,000 RPM the battery light would come on.

replace it now and save yourself some hassle.

 

[Spooky]

Still having this problem after changing out the belt and tensioner. Is a high output alternator worth it? I don't run any heavy electronics, but was considering a power inverter installed in the cargo area...would the HO work better for that?

 

[stamp11127]

Take your alternator to a local starter/alternator repair shop for testing. A good shop will be able to graph the output for the entire rpm range and provide the current output at each rpm step. If it passes then you are losing current to the field wire.
Only upgrade to a ho alt if you need the added amps. Otherwise your wasting money.

 

[splintrcel]

Its the alternator. My truck did the same thing and the amound of rpms you can put our will only decrease. Mine got down to not wanting to go past 2 k and i took it straight to auto zone and swapped it in the parking lot like 2 months ago. Change it now before your truck just dies all together while driving. Your lucky the alternator is giving you a heads up. Some just die instantly without warning.

 

[daoud elmassri]

Disconnect posotivet lead on your battery if it stalls out u need a new alternater if see stills running u need a new battery. Hope this helps.

 

[Spooky]

So, I went to Advance Auto and they tested the alternator.



Everything looked fine except that my Battery CCA was 1205.....it's supposed to be 750. Is that an issue? The tech said that I should swap alternators. What do you guys think?


Weird.....it won't let me insert a picture.............

 

[stamp11127]

I wouldn't change the alternator. Do you have a dvm? If so I would test the harness to the alt and also check the charging voltage out at different rpms.
Another thing to check is the position of the tensioner with the belt on. It should not be against the stop, should be around the middle of travel.
Google "how alternators work" and you will see what is happening in your case.
The battery is fine. An analogy would be a AA battery to a C battery. One just has guts than the other.

 

[Spooky]

Well, I went ahead and replaced the alternator. I had a mechanic buddy take a look at it and he thought it was a bad diode in the alternator. Changed it out and it no longer chimes or lights up under heavy acceleration.

On a side note, my idler pulley (the 6 rib one) wobbled a little bit. It looked fine, but still had a tiny wobble, so I got a replacement from Advance. I put the new one on and it wobbled too. I ended up grinding the tapered end of the bolt down a little bit and the bolt fit tighter and stopped the wobble....I thought that was kinda weird. So I just reused the old one and returned the new one.

 

[stamp11127]

Doubt it was the diode pack that failed

For those that are interested in how the voltage regulator works:
Designing a microcontroller-driven alternator voltage regulator | Embedded

 

[Spooky]

I don't know if it was a diode or voltage regulator, I just know it's fixed now. And because I threw some parts at it in the beginning, I have a new belt and pulley tensioner to go with it =D