ericem Posted September 4, 2009 Share Posted September 4, 2009 Hey guys, so it seems the voltage MIGHT be the issue to my idle wanting to go to 900rpm's in D at times. What I notice is when the voltage is around 11V in D for more then 3 seconds bam will start creeping to 900rpm's from 700rpm. Now it stays at 900 for a few minutes then starts going back down. Whats funny is when it brings up idle usually only goes to 12.1v max. Other times, the idle will be around 650 and the voltage at idle in D again will be 12.6v fans off still! Any ideas whats going on??? Tried a spare alternator same thing. Seems when the car is cooler can do 13.8v in D or N, but after driving a bit I am in that 11v- low 12v range. I am questioning maybe the fuel pump putting to much of a load on the electrical system yet my dad said it would have blown a fuse if it was that bad. Just suspicous how there is a melted wire for the main pump wire and was soldered together. So any ideas? Did the grounding mod like chassis engine etc. Also went over EVERY single ground point in the car and cleaned them same with battery terminals as well. Going to try a friends battery. Can't the alternator keep up without a battery technically or could the battery really be a issue still? Opinions!! Is my idle and the low voltage related you think? Already tried cleaning the IAC, and replaced the electronic part on the top. Car: 94 SS auto 207k km. Link to comment Share on other sites More sharing options...
Fairtax4me Posted September 4, 2009 Share Posted September 4, 2009 It could be the cables. I've seen more than a few old battery cables corroded from end to end underneath the insulation. Low voltage can do a lot of strange things. But voltage isn't the only thing to be concerned with. You should have the alternator's output checked with an ammeter. Most parts stores will do that for you free of charge. Is that affecting the operation of the engine? Maybe, maybe not. Usually you don't run into issues with voltage affecting the electronics in the car until you get into the 10v range, depending on the load. The electrical system is more efficient when it is cool. Copper wire conducts better, the alternator produces more. It's normal to see higher output voltage from a cold alternator than a hot one. Link to comment Share on other sites More sharing options...
ericem Posted September 4, 2009 Author Share Posted September 4, 2009 you know what actually when the fans are running after driving 30 mins or so the voltage is like 11.8 at idle then bumps the idle for a bit. When they shut off back to high 12 low 13 range at normal 700rpm range. So could the fans be bad or atleast one of them ? Or again normal ? Not 100% on the cables but they look good to me the car was rust proofed. Link to comment Share on other sites More sharing options...
Fairtax4me Posted September 4, 2009 Share Posted September 4, 2009 OH, so its doing that when the AC is on? It's probably fine then. Fans draw a lot of current. With 2 of them on at the same time plus the HVAC fan running you're probably drawing 30 amps off the alternator JUST for the fans. The ECU brings up the idle speed of the engine when the compressor is running. Mine jumps 300 rpm when the compressor kicks on, goes right back down when it goes off. Link to comment Share on other sites More sharing options...
ericem Posted September 5, 2009 Author Share Posted September 5, 2009 I am pretty sure its my fan motor. Tried a friends dry cell battery which has like 960cca made 0 voltage difference. I think my main fan is not spinning fast enough either. Going to swap in my fans from my other car. N/A and turbo fans should be the same right? Link to comment Share on other sites More sharing options...
Fairtax4me Posted September 5, 2009 Share Posted September 5, 2009 Don't see why not. A fan's a fan. If you plug it in and it starts turning backwards all you have to do is switch the wires. Link to comment Share on other sites More sharing options...
Cougar Posted September 5, 2009 Share Posted September 5, 2009 I doubt the fans are the trouble. The charging voltage is low from what you stated and you should be seeing up to 14.8 volts while the engine is reved to around 2,000 RPM. There may be a connection problem between the output lead (the large wire) of the alternator and the positive battery post. These points are basically tied together through a fuse and the wires. You could check the voltage across those points while the engine is running and there is a good load on the electrical system. If the wiring is ok there should be very little voltage drop across the wiring. Less than .1 volt. Also make sure the main output lead of the alternator is making good connection and isn't burned. Link to comment Share on other sites More sharing options...
Log1call Posted September 5, 2009 Share Posted September 5, 2009 The charging is playing up. It should never be below 12.5 whan it's running! Have you checked the belts aren't slipping? Checked for voltage drop between the alternators output and the battery? Checked for voltage drop between motor and earth? Link to comment Share on other sites More sharing options...
ericem Posted September 5, 2009 Author Share Posted September 5, 2009 Actually no forgot to compare voltage off the alternator!! Going to check today. Funny because I have compared other SS's and a TW and at 650rpm's with all lights on and fans kicked on its 13.5v that's why I am clueless. Hopefully it is something simple like the wire from the alternator to the battery. Now what I have noticed is if I am on the highway for a good 20 minutes (3k rpms steady) when I come to a stop the idle is about 650-700rpm and the voltage is around 13.2v with the fans on and maintains it for the few minutes I wait to see if it drops. Maybe because the engine bay is slightly cooler then sitting in traffic? Link to comment Share on other sites More sharing options...
Cougar Posted September 5, 2009 Share Posted September 5, 2009 (edited) The voltage is higher after being on the highway for a while because the battery has a better charge on it and it is helping to support the load. I would'nt be surprised if you found a connection problem between the alternator and the battery and assuming the fan belt tension is ok. Edited September 5, 2009 by Cougar Link to comment Share on other sites More sharing options...
987687 Posted September 5, 2009 Share Posted September 5, 2009 I've always had the low voltage at idle. When I idle my headlights noticeably dim. I always attributed it to a failing alternator. Link to comment Share on other sites More sharing options...
ericem Posted September 6, 2009 Author Share Posted September 6, 2009 Hmm well definitely not the fans. Voltage between the alternator to ground and battery to ground are the exact same. Thing is when the hood is popped things cool down a bit and the car makes 13.8v lol. Maybe replace the easy wires like main ground to the tranny bracket? Any other known issues? My only other concept is something is using alot of load I don't know what. When the fans cycle on with the hood open I am getting 13.7v. So confused why its so up and down. What tells the alternator to pump it up anyway? Link to comment Share on other sites More sharing options...
987687 Posted September 6, 2009 Share Posted September 6, 2009 What tells the alternator to pump it up anyway? The voltage/charge regulator. Which could be my issue too. It controls how much current is given to the stator, and thus how much the alternator puts out. Link to comment Share on other sites More sharing options...
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