I have a 95 F150 5.0 4x4, I bought it about 4 years ago with 36k ish miles and have put 30k on it with no issues at all. About a month ago I noticed heat would quit blowing when giving gas on incline mainly and checked forums and seen its most likely a vacuum leak. I tried looking at the white vacuum line on passenger side, but it looked ok, a few days ago at idle in gear( not in park) the engine shakes at random times like going over railroad tracks, when it does this I looked at gauges and the rpm always looks same, but I see the battery gauge is normally on the + symbol on gauge, when the engine makes that shake(feels like missfire) the battery gauge goes to the - on the battery icon on the gauge, once the stumple/missfire feel stops, goes back to +. I'm not sure if this is part of the vacuum leak causing the blower to stop coming out the vents or separate issue. I did a complete tunr up last year, plugs, wires new cap etc. In my head I'm thinking vacuum leak and possible bad alternator or battery going bad, but I dunno. Any help would be highly appreciated.

 

My gut tells me alternator too. The shifting into drive and having it shake is what really makes me think it because in park it is probably idling at a higher rpm, and then the shift to drive causes the rpms to drop and the need for power. But I'm guessing like you.

It's not a bad idea to change all of the vacuum lines in these trucks and replace them with 5/32" rubber or silicone tubing. The plastic crap they put on these trucks gets brittle and cracks. When I pulled them out of my truck one of them basically shattered in my hand. That would be what I would do first. Then I would see if you can find a local shop that can test your alternator. If it is fried, you should consider doing a 130A alternator upgrade.

 

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Yesterday I had the charging system tested and was told the alternator was bad, I replaced the alternator and the stumbling while sitting in drive 90% went away, but is there at random times it still burps. If I have the lights on and heater and let's say I put high beams on, I can see the voltage gauge go from the + to the - on the battery picture on the gauge, now I'm thinking maybe the belt is slipping on the alternator or battery issue. I tried to find any sign of a vacuum leak by spraying carb cleaner and couldn't get idle to change at all. Grrrrr

 

Battery may be going bad - assuming of course that all your connections (both ends) are shiny clean and tight. Sometimes a piece of sandpaper and an hour of crawling around the truck solves a lot of little issues - and keeps you from being stranded over a dirty connection.

 

I took it to a shop, said alternator was good and battery, but still having the issue with voltage drop in gear at idle with under load(lights etc on). Otherwise it's fine. They are trying a 130amp alternator next. Truck idles at 675rpm, could this be a issue causing less charge?

 

Problem fixed, the 130 amp alternator from a van fixed all my issues. Now voltage is constant, no dips, I can have ac, stereo on very loud with subwoofer, high beams on, wipers and guage stays on +! Not sure why the stock alternator 90 or 95 amp, can't remember, couldn't keep up at low rpms, but glad this fixed it. The shop tried 3 N7750 alternators, then tried a different brand before moving to the 130 amp.