I have a fairly new good battery and some days the 1995 f150 I have either will crank hard or not start without a jump. If i use the AC it will not start for sure the next morning. I see massive voltage drops when the AC or electric fan kick in. So my question is will it be possible just to upgrade from the stock alternator from 90 amps to 170 amps ? Or will I fry my whole electrical system?

Please let me know Thank you

 

Your starting problem is not the alternator amperage. I would suggest starting with the basics.

1. Batteryload test (can be done by any automotive retailer)
2. Battery cable inspection, including all grounds
3. Once started, voltage test.

Post your voltage results please?

Thanks,

Jeff

 

Upgrading to a higher amp output wont hurt, it supplies what your vehicle uses. Towing trailers with extra lights may require an alternator with higher output. Your problem wont be solved by an upgrade. Like the previous reply, ground wires are essential. All my vehicles have added grounds from block to frame, neg post of battery to the body and frame, etc. All heavy gauge wire to ensure I'm getting the best connection even when 1 is corroded. Clean those terminals if needed. Check the belt tightness to ensure its not slipping at all.
One old way to check the alternator is to to start it and remove 1 cable from the battery, either pos or neg. The engine bogs down but runs......alternator is good by supplying enough power to maintain. If it dies, alternator is junk. Check to make sure this old way doesn'tFUBAR the alternator like I read on a SAAB I worked on.once.

 

My vote is a dirty ground also. Check all your grounds and clean them. Just becuase they look good on top doesn't mean the connection isnt corroded, then hit them with a rustoleum or some kind of sealer so that they don't rust out after cleaning them. (This is after you secure the metal to metal ground of course)

BM

 

OK guys thank you for all your help! I checked my grounds and some were looking a little rough. I cleaned them off and tightened and sealed them up. That did have a little better improvement on my battery life. However....

WhatI failed to mention :

I installed and underdrive pulley kit and
a Flexilite duel electric fan. Which activated when the A/C is on.

These guys were pulling massive amount of juice and the underdrive pulley kit was not spinning my stock 95amp alternator nearly fast enough . SO I BROKE DOWN AND GOT A 170 AMP Alternator and the truck never ran better! It took 15 minutes and I couldnt be happier with the added juice! Thanks again guys!