Update: alternator and mileage - Off-Road Forums & Discussion Groups
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post #1 of (permalink) Old 01-11-2001, 01:31 AM
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Update: alternator and mileage

Just a quick note. Before my alternator burned out, I was getting about 10.5 mpg. After replacing it, I'm up to 13.5! Wow! Maybe the drag on the bearing as some said or reduced spark as others said, or both, but it certainly did help. Just wanted to pass that along and say thanks. This board is great!


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post #2 of (permalink) Old 01-11-2001, 01:37 PM
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Re: Update: alternator and mileage

Brad that's amazing !

I know on all my small block Mopars the same was true when my water pump bearings were on their way out.

After reading a few posts here or in another Bronco page I'm thinking seriously of upgrading to one of those newer 130 amp Mustang alternators. That ought to help the headlight brightness and stereo output too, though I can't complain about the stock system, I just want to do some preventative maintenance.

That comment about the stronger spark makes me want to pursue getting a stronger MSD type coil. I'm not sure the MSD control boxes will work with an 86 EFI system though the coil probably will.

Have you tried synthetic fluids in the axles, transfer case, motor and tranny yet ? They really helped my mileage.


86 Eddie Bauer 5.0 litre EFI, AOD, fully synthetic'd fluids, pussy truck/stereo pit

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post #3 of (permalink) Old 01-11-2001, 02:01 PM
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Re: alternator and headlights

The maximum output of the alternator isn't what makes the headlights bright or dim. It's the voltage regulator. Unless your alternator is running at its max right now, upgrading won't have any effect unless your regulator is bad and the replacement alt has a good one. But in that case, replacing the regulator is a lot cheaper - by about $140. The regulator is easy to install yourself if you have torx drivers and a paperclip (to hold the brushes back).

To see what's causing the dim lights, crank the engine and turn on all the stuff you normally drive with (don't forget the A/C). Then use a voltmeter to see what the voltage at the starter solenoid is. If it's less than 14, you have a problem with the alt or reg. If it's 14-15.5 at the solenoid, check it across the headlight bulbs. It should be 12.5-14.5V. If it's OK, your bulbs are just normally that color. (Check out the new "Cool Blue" line of GE bulbs.) If it's low there, check from the ground terminal of the headlight to the block. If it's more than .05V, clean and tighten the headlight ground screw (Haynes wiring diagrams tell exactly where it is). Otherwise, you'll have to trace the power wire back to the headlight switch to find the source of the low voltage.

Good luck.

83 Custom w/95 4.9L EFI, 78 NP435, 83 NP208, 83 D44IFS 3.07, 87 Ford 8.8ABS 3.08, Michelin LTX AT 31x10.50R15
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