2G Car voltage drops when below 1500rpm

AtrelleFrance · Jan 6, 2020

I'm about to take my 97 GST to a auto electric shop on the 27th and figured I'd ask the forums and see if someone would be able to guide me to a fix before then. My problem is the tach kind of stalls and jumps when getting up to speed, and when idling the voltages reads lower than expected on link causing cluster lights to sometimes appear to be off(the bulbs that light up the section of the cluster for the 5.5k rpm and redline). The interior and exterior lights will dim and then brighten a bit, hell you can hear the heater fans start to "slow down" at a stop light. Aside from the Tach jumping, my electrical problem goes away while driving and above 1,300-1,500 rpms. I've read and tried a lot of the things I've read on these forums, as well as facebook.

The car drives fine, Link shows the proper RPM readings(tach jumps when i get on it a bit), and the voltage reads 14.3ish while driving. Where the problems happen is when idling. I've read multiple threads already regarding this problem. I replaced the alternators multiple times. Started with remans then after 2 of them i went to the duralast gold 75amp, then to a duralast gold 90amp from the late 90s gen galant but swapped the pulley to match the one for the GST. Did the big 3 upgrade and did a couple redundant grounds in the engine bay. Even tried a power cable from the alternator straight to the battery but the problem still happens. Have put in a new alternator relay from mitsupartshop as well as a new alternator fuse.

As of now I'm just looking for some insight. This is my first post asking for some help before i shell out some money to have a shop deal with it so i can move onto the fun things.

ishnish · Jan 6, 2020

You're having similar issues as me. I, too, have numerous grounds to the point where I'm gonna start removing some. This is getting ridiculous.

What is your battery voltage at idle? I see yours goes up to normal when you drive. Mine doesn't

Also, have you relocated the battery?

AtrelleFrance · Jan 6, 2020

ishnish said:
You're having similar issues as me. I, too, have numerous grounds to the point where I'm gonna start removing some. This is getting ridiculous.

What is your battery voltage at idle? I see yours goes up to normal when you drive. Mine doesn't

Also, have you relocated the battery?

Battery is in the same location. Last time I had the battery checked the battery health was 89%, only like 3 months old and gave a "check ground/alternator" message. It's why I'm looking at electrical shops as my next go too because I want to move on to the fun stuff and I refuse to throw money at fun stuff just for the car to have problems. Sometimes on startup it will reset my glowshift boost gauge back to original color setting which is weird but has only happened twice since october LOL

ishnish · Jan 6, 2020

Crap I'm sorry my phone crashed LOL

let me update my reply

ishnish · Jan 6, 2020

Do you have a multimeter you can use? This way you can check the voltage of the alternator at idle. This is what I did. If that's showing more than what link says, you know your alternator is good and isn't the issue (provided it's a healthy range of 13.7v-14.x volts). Now the issue would be why your battery isn't getting that charge from the alternator. Check the wires running from the alternator to the alternator fuse. Pull the fuse box out and check that 100amp fuse on the alternator side. Should be a bolt that you just touch your positive prong on your multimeter to. If that's the same as your alternator, move on. If not and it's lower, bingo. If moving on, check the other side of that fuse (labeled "choke" on the fuse box) and if those values are under that of the alternator, there's your problem. If good, move on. The last spot would be those wires from the fuse box that go to the positive terminal of the battery, check the connections there. If lower than what the alternator is giving out, you have your answer. If not, then he'll idk because I'm stuck myself LOL

AtrelleFrance · Jan 6, 2020

ishnish said:
Do you have a multimeter you can use? This way you can check the voltage of the alternator at idle. This is what I did. If that's showing more than what link says, you know your alternator is good and isn't the issue (provided it's a healthy range of 13.7v-14.x volts). Now the issue would be why your battery isn't getting that charge from the alternator. Check the wires running from the alternator to the alternator fuse. Pull the fuse box out and check that 100amp fuse on the alternator side. Should be a bolt that you just touch your positive prong on your multimeter to. If that's the same as your alternator, move on. If not and it's lower, bingo. If moving on, check the other side of that fuse (labeled "choke" on the fuse box) and if those values are under that of the alternator, there's your problem. If good, move on. The last spot would be those wires from the fuse box that go to the positive terminal of the battery, check the connections there. If lower than what the alternator is giving out, you have your answer. If not, then he'll idk because I'm stuck myself

yeah i dont have anything tool wise except a 155 piece dewalt ratchet set LOL

. So im gathering all i can information wise so when i have a weekend day off i can go down to my buddies where we can do other tests. I'm content with spending the money to have professionals check it and fix

ishnish · Jan 6, 2020

I hear ya'. I'm getting pretty close to that point as well although I feel like I am also close to figuring it out. Funds are tight..

AtrelleFrance · Jan 6, 2020

ishnish said:
I hear ya'. I'm getting pretty close to that point as well although I feel like I am also close to figuring it out. Funds are tight..

I'm just multiple months into trying to figure it out that my first day of vacation I'm just dropping it off and letting them have their way i want the added security of it being done by a well known/recommended shop in order to save myself from the hassle so i can focus on restoring the interior, and then the body. This is just holding me back at this point. What worries me is if its the ECU because i know the alternator has the voltage regulator but the white cable coming from the Alt plug give the ECU the info and it can have power held for keeping the motor running and pulling power out of lights and other shit. At least that's what ive read on here a few months back.

miguelmcv · Jan 6, 2020

The ecu will kill the alternator only at high rpms, to help the engine at high load.

I read thread and I’m a bit confuse, I read rpm gauge does down and back up again, then the alternator not working at idle but good after that, so just update what exactly is your problem as right now.

If its charging ONLY at idle and everything check out
Ok, I would go and change the alternator pulley with a smaller one.

AtrelleFrance · Jan 6, 2020

miguelmcv said:
The ecu will kill the alternator only at high rpms, to help the engine at high load.

I read thread and I’m a bit confuse, I read rpm gauge does down and back up again, then the alternator not working at idle but good after that, so just update what exactly is your problem as right now.

If its charging ONLY at idle and everything check out
Ok, I would go and change the alternator pulley with a smaller one.

RPM gauge, when getting on the throttle, will kind of stall then jump-stall-jump.
The voltage reading i get off link is ~12v when idling. only time it pushes out normal voltage is when the car is above 13-1500rpm. otherwise it sits at 12ish volts until im driving.

both still problems. neither of them were fixed by all the stuff ive done thus far

AWD-Tony · Jan 6, 2020

What is your rpm at idle? How tight is your alternator belt?

It sounds like you may have two issues. One being a sticky tach and low voltage at idle as the other.

You can swap clusters with someone to see if the that fixes the tach.

For the low voltage, I’d check the connections and terminals starting from the alternator to the fuse box then to battery. Inspect all connections and terminals. Some will be crusty, so I’d clean them with sandpaper or file. Disconnect the battery first, clean and inspect both terminals as well

AtrelleFrance · Jan 6, 2020

tk106 said:
What is your rpm at idle? How tight is your alternator belt?

It sounds like you may have two issues. One being a sticky tach and low voltage at idle as the other.

You can swap clusters with someone to see if the that fixes the tach.

For the low voltage, I’d check the connections and terminals starting from the alternator to the fuse box then to battery. Inspect all connections and terminals. Some will be crusty, so I’d clean them with sandpaper or file. Disconnect the battery first, clean and inspect both terminals as well

RPM at idle is 1k after its warm.
I’ve tried a different cluster but the tach still ‘sticks’. And alternator belt isn’t loose, I thought it might’ve been slipping

miguelmcv · Jan 7, 2020

Have you calibrate ink for the battery voltage?.

When I log it in link, it shows different voltage to what the alternator was producing, check the voltage with something else to be sure it’s the actual voltage is reading link.

For the tach along, it could be the voltage (rarely happen), but I would go more to the crank sensor or the transistor going bad.

pay attention, when the tach goes bad, what’s the voltage at, if the voltage is good at the time the tach is acting, then the tach is not voltage related.

I hope you haven’t have any stall symptoms when driving, if you do, then the crank sensor is going out.

Pay attention and see what you can find and repost back to see how we can help.

AtrelleFrance · Jan 7, 2020

B

miguelmcv said:
Have you calibrate ink for the battery voltage?.

When I log it in link, it shows different voltage to what the alternator was producing, check the voltage with something else to be sure it’s the actual voltage is reading link.

For the tach along, it could be the voltage (rarely happen), but I would go more to the crank sensor or the transistor going bad.

pay attention, when the tach goes bad, what’s the voltage at, if the voltage is good at the time the tach is acting, then the tach is not voltage related.

I hope you haven’t have any stall symptoms when driving, if you do, then the crank sensor is going out.

Pay attention and see what you can find and repost back to see how we can help.

Voltage is good when I notice the tach acting up. Car drives just fine otherwise! And the sensors are brand new, motor only have 2200 miles on it at the moment

I’ll check again because maybe that might be that I’m not be calibrated but I dunno

miguelmcv · Jan 7, 2020

I used to see 12s and even 11s when idling and I had a really bad headache trying to figure it out, I even swap the alternator pulley with a smaller one to bump up the voltage at idle, however it did work but not the way I was expecting.

After looking and testing cable by cable to see how many amps I was loosing in each cable, I notes at the voltmeter the charging was good at idle, at that time It came to my mind to look at the log and see it was totally different then what I was seeing on the voltmeter, I calibrate link and swap the large pulley back to the alternator and forget about it.

AtrelleFrance · Jan 30, 2020

A bit of a quick update: went to the electrical shop on Monday. My problem came from the Green cable that comes off the alternator plug.

They ended up pulling the wire from the plug and wrapping the end so it doesn’t make contact with anything.

what does the green wire do exactly, why would that even be a problem? I’m assuming it’s a data plug that goes to the ECU, and I really don’t want the ECU to be my problem. And I’m currently on speed density so I can use the ECU that came with the car.

tunernewb92 · Jan 30, 2020

I would recommend this thread for your troubles.

https://www.dsmtuners.com/threads/alternator-trigger-wire.520037/

RWD4G63 · Jan 30, 2020

tunernewb92 said:
I would recommend this thread for your troubles.

https://www.dsmtuners.com/threads/alternator-trigger-wire.520037/

Just read through that, very informative. However, it's one of my favorite things when people think that more output from the alternator means it requires more "power" to drive

.

The Top DSM Community on the Web

2G Car voltage drops when below 1500rpm

AtrelleFrance

ishnish

AtrelleFrance

ishnish

ishnish

AtrelleFrance

ishnish

AtrelleFrance

miguelmcv

AtrelleFrance

AWD-Tony

AtrelleFrance

miguelmcv

AtrelleFrance

miguelmcv

AtrelleFrance

tunernewb92

RWD4G63

Similar threads

Latest posts

Build Thread Updates

Vendor Updates

Latest Classifieds