antnvlz1294

Hey Everyone,

I have an 1988 Mustang lx 5.0. I drive the car all day with no problems and I love it, although at night when I turn the lights on by themselves and or the heat on, the battery indicator on the dashboard lowers to less than half... I just bought the car on sunday and the guy said he replaced the alternator(it does look relatively new) and I was told it has a "newer" battery(a "Plus Start"). I replaced the sparkplugs, ignition wires and the distributor cap and rotor. With the lights and heat off(during the day), the car runs very strong. Although after trying to solve the problem by cleaning the grounds,(two skinny ones under the hood toward the front(cleaned as suggested)) it didnt fix anything. I started the car with no problems and turned on the lights(the battery indicator showed that it dropped a few volts) and drove down the road and stopped at the intersection behind a car. When i stopped the car idled a bit and then the rpms dropped and the car died. I started the car 3 times with the lights on although the car died right away all three times. I turned off the lights and the car started fine and I turned the lights back on and drove the car home. I cant figure out the issue? I just want to be able to drive the car with the lights and or heat on with the car acting up. The last two nights with the lights on the car started to "misfire" or "backfire" when I got to about 40-45mph between 1500-2000rpm. Has anyone else had this problem? Can anyone help?

Thanks,

-Velez

petrock

Start with the battery. First recharge the battery overnight and see if the problem reproduces by turning the lights and/or heat on. If not, then the problem is probably a weak battery. Take it to your local auto parts store and have them test it. They should do it for free. Age of a battery means nothing. They sometimes just go bad.

If the problem still repro’s after recharging the battery then whip out a volt meter and test the battery. It should have between 12.4 & 12.8 volts with the car off and 13.5 to 15 volts with the car running (idle). Then turn the lights on or turn the heat on and check what the voltage is. Then report back what you get.

antnvlz1294

Im going to go get the battery charged at a shop and then ill try the lights and heat suggestion. However i dont have a battery charger or a multimeter...

88 orangepeel notch

Do you know if the po had underdrive pulleys on this car?

antnvlz1294

Got my hands on a volt meter. Put negative on negative terminal and positive on positive terminal and this is what i got. With the car off i got 12.57 volts, with car on no lights or heat i got 14.42 volts and finally with the car on with lights and heat on i got 12.8 volts.. is it just a dirty or loose ground then...? An no to the underdrive pulleys.

mattdel

Stock alternators put out a whopping 60 amps. If you want the dip in voltage to go away you'll need to do a 3G upgrade. They come in 110 and 130 amps.

petrock

That much of a voltage drop says to me that you have a short somewhere in the headlight and/or heater circuits, or a weak battery. An alternator upgrade isn’t a bad idea, but I don’t think it will fix your problem.

Most autoparts stores will test a battery & alternator for free. Call ahead and bring it in.

Do you have any aftermarket electronics installed like an amp, security system or something? Maybe something that is piggy-backing on the headlight or heater circuit?

antnvlz1294

I dont have anything piggy backing... the only parts I have that are not stock is the Cold air intake, the headers, exhaust and the short throw shifter.. Ill definitely have them test the battery and alternator and see what the issue is, how would I find a short? Keep in mind that the cars volts would drop even with just the head lights on and it will still run rough. The heat just makes it worse. Ill try buying another battery next tuesday(when I get paid and ill be sure to buy an upgraded 130amp alternator and kit but does anyone have the link for that? some places want $300 + for one?, and I know theyve got to be cheaper than that. I'm going to check my grounds any way just to be safe.

antnvlz1294

Whats a really good brand 130amp alternator? Do you have a link? Because the one's i'm seeing are going for $300+...

petrock

You could try your local junk yard. My wifey’s ’98 3.8L came with the 3G alternator (130amp) stock. I don’t know what other models/years came with it, but I know it was a very popular alternator for a number of years in Fords.

That $300 probably has a core charge included. If so, when you give them your old alternator they give you some money back.

As for where to buy one I would check out rockauto.com. They have 130A 3G alts ranging from $100 to $200 (minus core charge). Note: you do get what you pay for with alternators. Make sure which everyone you buy has a good warranty.

I don’t know if the 3G alternator is a direct bolt on for your ride though, so do your homework before putting money down. There are probably write ups on this forum on how to do the upgrade. Keep in mind that there are different model 3G alternators where the only difference were the mounting whole locations. So make sure you get the correct one.

Good luck...