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Old 12-29-2016, 06:01 PM
tensley tensley is offline
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Join Date: Apr 18, 2014
Location: Alabama
Posts: 25
Low voltage in drive

Hey guys. On my 1991 JGW I finally got my power seats, rear defroster, and rear key switch fixed. It was a fusible link, however here is my new problem. While running in park the voltage gauge reads around 14.5-14.7. As soon as I put it in drive (not moving) the needle drops down to around the low 13 or below 13. Put it back in park it jumps right back up. While I'm driving it is around high 13 to low 14 but as soon as I come to a stop sign or red light it drops right back down. My battery is new and I had my alternator checked last night at O'reillys and it checked good. This all started last week after replacing the fusible links. I know they are good because all of the devices are still working with no problems. Is there anything that I still need to check or do? I'm at a loss. Thanks
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Old 12-29-2016, 10:54 PM
Joe Guilbeau Joe Guilbeau is offline
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Join Date: Apr 17, 2002
Location: San Antonio, Texas
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Exclamation No problem...

Quote:
Originally Posted by tensley
Hey guys. On my 1991 JGW I finally got my power seats, rear defroster, and rear key switch fixed. It was a fusible link, however here is my new problem. While running in park the voltage gauge reads around 14.5-14.7. As soon as I put it in drive (not moving) the needle drops down to around the low 13 or below 13. Put it back in park it jumps right back up. While I'm driving it is around high 13 to low 14 but as soon as I come to a stop sign or red light it drops right back down. My battery is new and I had my alternator checked last night at O'reillys and it checked good. This all started last week after replacing the fusible links. I know they are good because all of the devices are still working with no problems. Is there anything that I still need to check or do? I'm at a loss. Thanks

Your alternator must replenish the amperage given up by the battery when starting, so it's regulator is putting out 14.5-14.7Vdc, this is normal, putting the vehicle in drive provides a load to the engine, and therefore its RPM level drops and therefore the alternator drops output simply due to the fact that the engine spinning the crankshaft pulley at a lower revolution and therefore the belt is spinning slower, and therefore the alternator pulley is spinning slower, and therefore the alternator's output is lower...by design.

Try standing on the brake in drive and press the accelerator to get the rpm's higher, the voltage should go higher.

Make sure you close the garage door and pull right up to it and do the above experiment...
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Joe Guilbeau<br />1983 Cherokee Laredo WT (SJ-17), 360/229/727/D44/D60 4.10 Gearing, 8-lug hubs, Edelbrock Performer w/EGR Intake, Mallory Unilite Series 47 Photo-Optic Infrared Trigger Vacuum Distributor, Mallory Surge Protector, Mallory Promaster Coil, Holley Pro-Jection TBI 502-Analog, FlowKooler High Output Water Pump, Staggered 4-Core Custom Industrial Radiator, HD Fan Clutch, Dual Electric Fans, CS130 Delco 105-Amp Alternator, Oil Bypass Mods at Rear of Block and Distributor Oiling, Superlift 4\" Suspension, Rancho RS5000\'s, Hi-Tech 31\" Re-Treads, Aero 33 Gal Tank w/Skid Plate, Custom Rear \"Longhorn\" Bumper
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Old 12-29-2016, 11:15 PM
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ZackN920 ZackN920 is offline
350 Buick
 
Join Date: Nov 18, 2015
Location: Stephenson County, IL
Posts: 932
Quote:
Originally Posted by Joe Guilbeau
Make sure you close the garage door and pull right up to it and do the above experiment...

WHAT?! I hope your kidding!

Hey tensely, You still got the stock alt in your Wag? If so, sometime upgrade to a CS-144 alt and you shouldn't have any issues. Previous owner did that to my Wag, and I got great power. Only time mine will dip is if all the lights(including fog's) are on, the AC is on high, and at a stop in gear at low idle.
From what i've read online, the stock alt is barely rated high enough for the stock GW. After a number of years and miles worth of use are on it, it is bound to get weaker with time and then, there ya go....low power
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1990 Grand Wagoneer-"Big Jeep"
AMC 360, TF727, NP229, 2.72 gears, 2" lift
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...not too rusty anymore
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Old 12-31-2016, 06:21 PM
Joe Guilbeau Joe Guilbeau is offline
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Join Date: Apr 17, 2002
Location: San Antonio, Texas
Posts: 2,137
Quote:
Originally Posted by ZackN920
WHAT?! I hope your kidding!

OK, you got me, just wondering if anyone actually reads this stuff... don't forget to holler "Watch This!"
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Joe Guilbeau<br />1983 Cherokee Laredo WT (SJ-17), 360/229/727/D44/D60 4.10 Gearing, 8-lug hubs, Edelbrock Performer w/EGR Intake, Mallory Unilite Series 47 Photo-Optic Infrared Trigger Vacuum Distributor, Mallory Surge Protector, Mallory Promaster Coil, Holley Pro-Jection TBI 502-Analog, FlowKooler High Output Water Pump, Staggered 4-Core Custom Industrial Radiator, HD Fan Clutch, Dual Electric Fans, CS130 Delco 105-Amp Alternator, Oil Bypass Mods at Rear of Block and Distributor Oiling, Superlift 4\" Suspension, Rancho RS5000\'s, Hi-Tech 31\" Re-Treads, Aero 33 Gal Tank w/Skid Plate, Custom Rear \"Longhorn\" Bumper
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Old 01-01-2017, 12:22 AM
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serehill serehill is offline
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Join Date: Nov 22, 2009
Location: Mesquite Texas
Posts: 8,619
it could be more simple.

Check your Idle RPM it simly could be too low. Voltage does drop at idle though.
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80 Cherokee
360 ci 727 with
Comp cams 270 h
NP208
Edlebrock performer intake
Holley 4180
Msd total multi spark.
4" rusty's springs
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If you can't make it better why waste your time. No use repeating the orignal mistakes. I'm to old to push it that's why.
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