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Old 05-10-2019, 09:19 AM   #1
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Default Voltage Drop and Lights Dim when Coming to a Stop

Now that the SECURITY issue is fixed and the car is driving... Thanks to this forum and the Harbor Master. Got another problem I'm battling that I need some help with. Looking for some tips into what could be causing this on-going issue that I'm experiencing in the same 2000 Turbo Prix. Maybe the ignition issues I described in my previous and this issue, are related?

Whenever I'm coming to a stop, whether pressing on the brake pedal or just coasting to a stop, my voltage drops like a rock. At idle is stays constant at 14.3 or higher. When driving it's around 14.2v or higher. When coming to a stop however, the voltage drops to as low as 9.8v.
I have a quick, 20 second video of it happening below. Watch the Aeroforce in the top left corner. Numbers jump from 14.2 > 10.8 > 13.5 > 14.1 > 11.1 > 13.7 > 11.2 > 14.1 ...etc

Things I've done already:
Scrubbed, sanded, scrapped all grounds. EXCEPT for the under carpet grounds in the cabin.
Replaced IAC sensor with brand new AcDelco sensor.
Cleaned MAF sensor


VIDEO:
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Old 05-10-2019, 09:24 AM   #2
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The voltage can only drop to as low as the battery is, so if the battery is over 12v, which I assume it is, I'm not really sure what you're seeing there.
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Old 05-10-2019, 12:30 PM   #3
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Hmmm... Didn't think about that. That's a good point.


So maybe bad battery? I can swap in the one from the maroon GTP and test. That battery is new.

Now that I think about it, I remember PO telling me that the car has the ZZP voltage booster dongle. Maybe that's causing issues. It's been known to do spooky things. That's an easy and obvious one, gonna start there. Gonna remove the booster and see what happens.
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Old 05-10-2019, 12:40 PM   #4
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Agreed, that's a good start. Whilst you at it, just peep the battery voltage, but if it starts the car, I highly doubt it's under 11.8-12.2-ish volts.
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Old 05-10-2019, 12:41 PM   #5
 
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Do you have a volt meter? Test the voltage with that, test the battery with the car off and the alternator when it’s running, I don’t remember if all the gp alternators have a clutch pulley or not but maybe it’s going out
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Old 05-10-2019, 02:26 PM   #6
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Quote:
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Agreed, that's a good start. Whilst you at it, just peep the battery voltage, but if it starts the car, I highly doubt it's under 11.8-12.2-ish volts.
Car starts without any issues. When I was doing that security relearn yesterday with the key at ON position, the Aeroforce displayed 10.3v

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Do you have a volt meter? Test the voltage with that, test the battery with the car off and the alternator when itís running, I donít remember if all the gp alternators have a clutch pulley or not but maybe itís going out
I don't have a volt meter. But I should by now! Dohh! Will buy
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Old 05-10-2019, 02:30 PM   #7
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I don't have a volt meter but I do have a spare alternator! Borrow it from the red car if I need to!
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Old 05-10-2019, 05:40 PM   #8
 
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Iíve had a similar issue on my turbo 04... idle in park 14.2-14.4. Get driving and come to a stop and the voltage drops to 11ís and 12ís. Seems to mess with my fueltrims as I can see the wideband go wonky. I replaced the alternator which did nothing, however my battery was crap so that was my next step.

I havenít driven the car yet this year but did buy a new battery so Iím gonna go from there. Clean up some grounds too since I have it out. I know I need a tensioner, doubtful that that is causing my issue though... I think..
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Old 05-10-2019, 07:24 PM   #9
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I was thinking battery/wires/connectors as soon as I read your post. If it's the battery, you'll find out soon enough.

Stop at an auto parts store and have them check it or toss in a battery from another car and see what happens.
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Old 05-16-2019, 12:26 PM   #10
 
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Iíve had a similar issue on my turbo 04... idle in park 14.2-14.4. Get driving and come to a stop and the voltage drops to 11ís and 12ís. Seems to mess with my fueltrims as I can see the wideband go wonky. I replaced the alternator which did nothing, however my battery was crap so that was my next step.

I havenít driven the car yet this year but did buy a new battery so Iím gonna go from there. Clean up some grounds too since I have it out. I know I need a tensioner, doubtful that that is causing my issue though... I think..


Just to update I did change the battery and have been driving the car. Seems to hate coming to a stop the idle and volts dip down, stalls sometimes.. when it doesnít stalk voltage doesnít recover unless I tap or use minor throttle.

Possibly gummed up throttle body? It is DBW. Or maybe the fact Iím probably down a hole compression wise causing vacuum issues messing with the tune? Iím pulling at straws. Probably gonna get rid of it relatively cheap, but itís still fun to drive even on 5 (and 1/2 cylinders).
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Old 05-17-2019, 10:27 AM   #11
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I put in my spare battery - No Change
Removed ZZP Voltage Booster - No Change

Next up is an alternator swap, and going to go ahead and replace ignition switch/harness. Also, I've done some reading and it appears that a bad brake booster could be causing this. Doesn't look like a fun job.
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Old 05-17-2019, 10:31 AM   #12
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Bad ground?
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Old 05-17-2019, 10:52 AM   #13
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I've scraped all grounds raw. Scrapped, sanded, wire brushed, finger-nailed (lol)... they are clean! EXCEPT for the 2 under carpet grounds.

I was avoiding them because you have to remove the plastic molding and lift the carpet, but at this point they need to get looked at.
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Old 05-17-2019, 11:09 AM   #14
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Quote:
Originally Posted by CHI2000GTP View Post
I've scraped all grounds raw. Scrapped, sanded, wire brushed, finger-nailed (lol)... they are clean! EXCEPT for the 2 under carpet grounds.

I was avoiding them because you have to remove the plastic molding and lift the carpet, but at this point they need to get looked at.
Probably easier to get to then the alternator
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Old 05-17-2019, 11:21 AM   #15
 
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Quote:
Originally Posted by CHI2000GTP View Post
I put in my spare battery - No Change

Removed ZZP Voltage Booster - No Change



Next up is an alternator swap, and going to go ahead and replace ignition switch/harness. Also, I've done some reading and it appears that a bad brake booster could be causing this. Doesn't look like a fun job.


What or where did you hear about the brake booster? Iím guessing some sort of vacuum issue especially since itís low rpms/idle.
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Old 05-17-2019, 12:23 PM   #16
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Yep. Could be the booster leaking vacuum. Read about it on a Firebird forum. I will search my history and find the link.
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Old 05-17-2019, 01:06 PM   #17
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Quote:
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Probably easier to get to then the alternator
That's true for this Turbo Prix because the alternator has been relocated to where the A/C Compressor was. And the coil packs moved to the firewall kinda where the alternator originally was from the factory. It's still rather easy to get to tho.

Otherwise, on these 3800 engines the alternator is one of the easiest parts to remove. Right on top of the engine, next to the coolant overflow, and only 3 screws holding it in.
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