Will low voltage cause problems?

Discussion in 'SVT Tech Forum' started by zerbrenny, Jul 31, 2007.

  1. So I really need some help here. I was driving my 03 Cobra into work yesterday morning and I felt like something wasn't right with the car. Half way to work - when I would give it gas at highway speed - it would bog out almost like the traction control was kicking in. As soon as I got off the exit the car died and my instrument cluster went wacko right before it went dead.

    I had dim dash lights and it seemed like an easy diagnoses to me battery dead = bad alternator. So I went to the store and picked up a "red top" Optima battery. I installed it at work and the car ran fine. I figured I could get the car home on the battery. Replace the alternator over the weekend.

    Long story short the car died again just as I pulled into the driveway. I ordered a new alternator from NAPA but it is taking a few days to arrive (special order).

    Here is the problem:

    When I started the car today it sounded like a can of marbles!! It sounds like I threw a bearing or something. Could the lack of volts be causing this to happen? Or did I mess it up driving it home on just the battery? Will the new alternator make the horrific noise go away? I am thinking the computer is messed up due to low voltage? U. M. what do you think?

    If any of you guys have some input I would appreciate it! If I F'd up the motor I will be pissed! :nonono:

    And if it is bad anyone know of a reputable shop in the Pheonix, AZ area? :shrug:
  2. I can tell you the alternators on the 03/04 Cobra's are a high failure item. Most guys find the aftermarket replacements for the Cobra's alternator are sub par at best.

    You say you've replaced the bad alternator once already. With what brand may I ask?

    Often when someone says their car sounds like marbles rattling in a can they're actually describing piston slap which is common in a engine like ours and is not a big deal. The noise however usually dissipates once the engine is up to full operating temperature.

    Maybe the replacement alternator you installed over the weekend is making the noise you're hearing?

    I'd wait and see what she sounds like once the new alternator is installed.

  3. We see this on the dyno from time to time. That's why we always log battery volts during a pull. What happens is the voltage gets too low and the fuel pumps crap out and the car goes lean. Can also cause injector problems and ignition problems. Not to mention you have an IC pump that also is affected.

    If you got on it and any of this happened, it'd have the same result as inadequate fuel pump. Hopefully, you didn't hurt anything and the alternator will fix it all.

  4. I never considered the low voltage could possibly cause a lean condition because the fuel pumps weren't getting enough juice thusly reducing the total pressue output to the injectors and rails.

    Lets hope he didn't hurt the motor...

  5. I know someone that recently had a problem with a lower quality alt. cause feed back into the system and giving off faulty check engine lights because of it. I would definatly go with a high end replacement it will be fewer problems in the end. Also could the noise be from failed bearings in you current alt?
  6. Thanks UM and the rest of you guys for the response; I have not replaced the original alternator yet that went bad, it is still sitting in the car. Someone else at work suggested it could be a loose bearing from the bad alternator making the noise - I hope that is what it is. I haven't bothered taking it apart yet because I don't have the new one. I will keep you guys posted on the outcome, keep your fingers crossed. I haven't slept well - it's like one of my kids is sick.
    The alternator is due in tomorrow from NAPA. I was going to splurge on a PA alternator but I couldn't justify the 300+ dollars for one. I will let you know the brand, I forgot the name.

    What about a mustang shop in the Pheonix area? :shrug:
  7. Don't know of any shops in that area. I would suggest you try the Southwest regional forum but it looks pretty slow in there so I am not sure what kind of replies you would get. Might take a look at some of the other forums out there to see if they have more activity for your region.
  8. OK guys here is the update, got the alternator in and dispite the fact that it is working I still have the noise. I don't think it is coming from the motor, but then again it is hard to isolate. I think I will have to take it to a shop :nonono: It almost sounds like the time I blew my clutch on my 98 GT but the clutch is functioning properly and I don't think it would kill the power on the car. (power as in acceleration)

    It's funny, the noise doesn't go all the way through the RPM range and the car exhibits poor power. I am going to look through some simple trouble shooting tips, but I am at a loss. :shrug:

    I will write another update when I learn more.
  9. Well I work as a tech. for chrysler and I can tell you one thing. Low system voltage causes all kinda of problems, and driveability issues. The 4.0's are especially finicky when it comes to battery voltage. Even I myself have had issues with mine with battery voltage too high and low, and a buddy of mine with a C5 had serious issues with driveability with low voltage. As far as the noise you have, a friend of mine has an 03 Cobra we get to mess with all the time and I know the IC pump is a problem with these Cobra's apparently *hes gone threw 2 in 70k miles* And he is on his 3rd alternator. So dont feel bad your not the only one who has issues with his cobra.
  10. OK guys, here is the deal. I am going to man up and admit my mistake here. Turns out at the same time I had the alternator problem, the "noise" I was hearing was actually a loose mid pipe! That was the noise and loss of power I was experiencing. It was only hanging on by one nut. So since the car was already in the shop and the wife was under the impression that the car was "broken" I had a Metco 10" lower pulley done (yes I changed the alternator pulley) and after adding a Bassani X pipe and a JLT high boost CAI I am turning 430HP and 498 torque! :nice:

    Next time I will take a closer look under the car instead of panicking. Thanks for your help guys!
  11. Torque is unusually high compared to horse power. need to see that dyno sheet with A/F ratio. Something is off.