Strange Alternator Problem

[Marc87GN]

It was a little warmer out tonight(about 55) and I took the car out for a few sessions of tuning. I see that I'm able to run 20-21 psi on 93 octane with 17 degrees of timing with zero knock. I have the alert setup so if it knocks above 1 degree, the computer plays music so I can watch the road. I had 1.1 degrees at 97 mph, but the O2s were in the mid 800s until it dropped to 782. The strange part is the voltage from the alternator went from 13.5-6 to 11.5. I also noticed the headlights dimmed. Later I made a few more passes with no knock, but the alternator seems to cutout at about 5200-5300 rpms. This is a new 140 amp alternator and should be enough to support everything or so I thought. Is there that much current being drawn or is the alternaor faulty? All of the grounds are on tight. It just seems strange.

 

[83ttypecooled]

alt. output

Hi,
Beyond belt slippage,I can't think of a whole lot of possibilities here. That doesn't mean there are none, however. The alternator charges normally the rest of the time, huh? That 140 doesn't have a microchip in the regulator, does it? Your problem sounds eerily like one I experienced with a 2003 Mustang cobra.The customer did a lot of high speed driving, and was complaining about poor lighting when he got on it. I took it for a test drive(this was fun!),verified his complaint. I did some homework, found out that on 85% throttle, alternator is disabled by the PCM. As much power as that car has, I think Ford could have left the alternator hooked up. However, I digress.... I have never heard of such controls on our cars, so must advise that you are probably dealing with an ALt. failure,if the belt isn't slipping. You would hear that, right? Good luck with your trouble.

 

[Marc87GN]

Hi,
Beyond belt slippage,I can't think of a whole lot of possibilities here. That doesn't mean there are none, however. The alternator charges normally the rest of the time, huh? That 140 doesn't have a microchip in the regulator, does it? Your problem sounds eerily like one I experienced with a 2003 Mustang cobra.The customer did a lot of high speed driving, and was complaining about poor lighting when he got on it. I took it for a test drive(this was fun!),verified his complaint. I did some homework, found out that on 85% throttle, alternator is disabled by the PCM. As much power as that car has, I think Ford could have left the alternator hooked up. However, I digress.... I have never heard of such controls on our cars, so must advise that you are probably dealing with an ALt. failure,if the belt isn't slipping. You would hear that, right? Good luck with your trouble.

I thought it might have been the belt slipping as well, but I installed a new Dayco belt a few weeks ago. it charges perfectly fine all of the time, but when I'm at full throttle the voltage drops. I wouldn't think it would slip all of the time. I thinkthis problem is causing my slight knock problem because when the voltage stays up, I don't get any knock and O2s in the mid 800s. Oh well, I will try a volt booster and if that doesn't work, I will try another alternator. I just swapped in the new shortblock so I know all of the grounds are nice and tight. I also updated the hot side with a thicker cable. Maybe I should order a new ground cable.