my 93 f-150 4.9has a new battery,alternator,starter,computer(from the boneyard.The problem is when its running the gage reads fine(ammeter).When i turn on the heater it drops voltage,then returns to normal.Then I turn the lights on same thing.But with both the heater and the lights on and the damn thing in drive tha gage just drops and stays there nearer the r in normal.If i give it a little gas it will jump up to where its suppose to be.Alternator is pusking out about 14 volts but its down in the 11"swhen eveything is on and its in drive.Any suggestions? Thanks

 

If you find out what the problem and fix is please let me know. I asked this about a month ago. I still haven't found out what is causing this on my truck either. Truck is fine until I put it in drive with lights and heater on. Then voltage drops way down to about the o in normal. If I give it a little gas and keep the rpm's around 8 or 900 it is fine except for an irratic idle. The truck will also sometimes want to stall if I let it go too long without giving it a little gas at a stop light as the voltage drops. I have put in a new battery, alternator, EGR valve and sensor, new oxygen sensor also. Cleaned the throttle body and throttle plates. Checked the IAC and that is not dirty so I put that back in. Added new air filter and crankcase filter. Checked pcv valve and it is fine and the hose isn't blocked either. I have run out of info on what to check or try. Any help would be appreciated. Thanks

 

As far as the voltage drops go there are a couple of things to look . First being the battery cables , not just whether the terminals on the battery & cable ends are clean but the internal condition of the cables . If the voltage is having trouble completing the path then you will have troubles with electrical components that require a lot of power such as the lights & blower motor . Also if the blower motor itself is drawing more power than it needs then its going to put a strain on the whole system .

 

I had an `87 Ch*vy Blazer that did something similar, started fine, but put it in reverse to back out of parking spot, stalls. Leave it running, hit the lights, whole dash goes dead, I fixed the stalling thing when I replaced the battery cable (god that postive cable to the starter was a real b!tch to install!) but the lights on dash dead thing stayed, eventually I found it was the after-market fog lights I had on the truck, I unplugged the lead for the fog lights from the battery and everything worked fine, didn't matter that the lights were off, something was up with the wires to them, you might want to look at ALL of the things you've got plugged in, even in the cigarette light, especially if you're drawing high amps with big lights or stereo.

1995 F-150 XL Reg Cab/Bed
http://members.sounddomain.com/blind
5-star rated F-150 (big stereo)

 

Bad diodes in alternator?




2000 XLT Flare Supercab Sport 5.4-Auto-355LS-Tow pkg-Bedrug-Xtang Tonneau

 

I'd say either the bearings were going out, or the diodes are bad. Take it to a local parts house, they should test you charging system for free. Sounds like what happened to my alternator. I replaced the diodes and bearings.

 

Changed all battery cables ... no luck same thing.Redid all grounds....same thing.Nothing extra plugged in (all stock)Maybe the gauge....next warm spell........its history...lol thanks guys...............................Bill

 

Hello, I have a 96 that is doing the same thing. I have a new alternator, and a new H.D. battery, and it still does it. I have talked to plenty of other 92-up Ford owners, and they all have the same issue. As of 97, Ford has an optional 130amp alternator available on the F150 I believe. I tried to get this for my 96, and they don't even show it as an option...even in the F-250!! I read in another group that a guy had a mustang and he re-did the harness so it would accept a 130 amp newer alternator. If anyone is interested, mail me and I'll see if I can dig it up.

Rich
rdtect@snet.net

 

No firsthand experience (yet) with this swap, but I'm told a 75 amp alternator is a bolt in for the stock 60 amp. There's even another set of mounting holes on the bracket on my '93. Mine seems to take a long time to recharge also but I haven't had any starting problems, even the morning the thermometer read -22.

Trail Rider