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Discussion Starter · #1 ·
Hey everyone,
98 gt 4.6l. Voltage drops slowly when under a load. ( headlights, ac, radio on). I've replaced the alternator 3 times and the battery 2 times. I took it to a shop. The mechanic told me that my car has a under drive pulley kit on it and my alternator pulley was to big so it wasn't spinning fast enough. I did the research and got the right size pulley. Still the same issue ALTHOUGH it will hold a over 14v when just the ac or the headlights are on but once I put turn them both on it drops slowly under 13.2v. When I Rev the engine it will climb which I know it supposed to but then drops once at idle when both ac and headlights are on.

All grounds are clean and tight and I have brand new battery terminals and there tight.

Also my cluster lights have a light flicker at idle but once I'm at a higher RPM they are steady.

Sorry for long post. I wanted to give all details on the situation. I am just at a dead end. ANY input would be great. I'm going nuts over here trying to figure it..

Please any responses would be greatly appreciated.

Thanks

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Did you change the just the alternator pulley? Or did you replace both the alternator and the crankshaft pulleys?
Have you closely inspected the connections at the alternator?
What brand of alternator are you using?
 

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Discussion Starter · #3 ·
When I bought the car it came with underdrive pulleys. I was not aware of it. The mechanic measured the crank pulley and he said it was after market and part of the underdrive kit. So when he gave me the measurement I doudle checked it and then did the research on line and ordered just the alternator pulley for it.

As for connections on the alternator, I did change the pigtail on it because I noticed it was showing bare wire.

It's a Motorcraft alternator.

I even changed the belt. the belt tensioner is nice and tight.
Thanks for replying, can you think of anything else I could be missing???


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My Bullitt came from the factory with half of the underdrive pulleys... Ford put them on all of the accessories and left the crankshaft pulley the original diameter. I'm not sure that your problem is related to that though.
This is a tough one! You've checked off all of the "easy" to diagnose items.

What RPM's does the engine idle at?
 

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Discussion Starter · #5 ·
It idles from about 850 to 1000.

Would a bad pcm cause this??

From research I've done it controls a lot of the electrical components. But nothing else is acting up in the car expect for what I've posted.

Should I check the diameter of the harmonic balancer again.


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Since your engine seems to be idling a little fast, you can probably rule out the pulleys for now.
It seems like one of the accessories is possibly drawing more amperage than it is supposed to. I would focus on trying to find a faulty wire or ground. Possibly related to the headlights. When the AC is on, the engine cooling fans are also running, along with the HVAC circulation fan. So those could be another possibility.

Does the charging light turn on when the car is idling with a full electrical load?
 

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A quick way to check the alternator to battery connection is with a voltmeter measuring the drop between them. Connect a digital meter + to alternator 14 volt output and - to battery positive terminal. With engine idling anything over say 0.5 volt means there is excessive wiring resistance.

If this checks out then something like straybullitt says is pulling too much power. If you can feel any really warm wires or connections that's a big clue :thumb:
 

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Discussion Starter · #8 ·
The charging light doesn't come on.

I will check the voltage and see if I'm getting the right reading.

I'm currently preparing for a hurricane that's getting close to fl.. once I check it I will get back to you guys with the results.

Thanks for the info.

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Discussion Starter · #9 ·
Hey guys,

Sorry it took me so long to reply back. I've been extremely busy since that storm.

Anyways I checked the voltage from the ALTERNATOR POST AND THE POSITIVE BATTERY POST and I'm getting a 0.33 reading at idle with nothing on. Is that good???

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I have had a similar problem my battery light wouldn't come on in the cluster and alternator wasn't charging the battery. I even went as far *** pulling the cluster to make sure the bulb wasn't dead. Turns out the pigtail that goes to the alternator one wire was bad. Found it by poking a test meter a few inches back. Replaced the wire and was good to go
 

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That was my issue too its in one of my threads good you got it figured out

xxr staggered 17's, ford racing c springs, tokico blue struts, koni orange shocks, shorty billit antenna, billit gas cap, UPR CAI, UPR O/R Xpipe, Magna flow exhaust, Mach1 grill delete w/ chin spoiler, honeycomb blackout, Bama tuned 93 OCT. V2
 

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Discussion Starter · #12 ·
I replaced the pigtail. What volts should those be reading??? And when I replaced it I spliced into it. I will look there again but there are 3 cables that are in the pigtail. What voltage should each one read??

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Above 13 withe igniton on on all wires the 0 with the ignition off on one wire

xxr staggered 17's, ford racing c springs, tokico blue struts, koni orange shocks, shorty billit antenna, billit gas cap, UPR CAI, UPR O/R Xpipe, Magna flow exhaust, Mach1 grill delete w/ chin spoiler, honeycomb blackout, Bama tuned 93 OCT. V2
 

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Discussion Starter · #14 ·
Sorry it took so long to reply back.

I checked the voltage at the alternator pigtail. The one that's always hot reads 12.7v and the one that is only hot with the ignition on also reads 12.7v.

Is this ok??

Also my dash lights have a light flicker at idle even tho its at 14.5. Once I give it gas or I'm cruise it doesn't flicker anymore..

This has been a crazy ride trying to figure it out.

Anything else I'm missing. Is the voltage at the pigtail correct??

You think it could be the mega fuse????

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