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94 F150 w/ 4.9L "Y" VIN Charging problems

Help. My alternator failed on Christmas Eve. I replaced it on Friday and found out on ithe old one took the battery with it to the grave. I replaced the battery yesterday. The alternator worked fine yesterday (~14.5 volts) until I put the lights on, then it dropped below

12 volts and never recovered. I drove it last night around town and it drained the battery. When I drive on the highway it just barely makes 12 volts. I used dielectric grease on the connectors on Friday, found out what a mistake that was today. I cleaned everything and nothing looks damaged. The battery is showing ~ 11.85 volts before starting. I start the truck and it runs around 12.25 volts until I run the rpms up to 1500-2000, then it shows around 13 volts. When I turn the lights and heater on (full load) the voltage drops to 11.85 (original battery reading) which I believe means that everything is now running off the battery.

I've got 2 procedures to check the charging system, one from the Haynes manual and the other from Mitchell On-Demand (on-line repair manual). The 2 do not match. The Haynes says 14-15 volts, turn everything on and get a drop then recover to 14-15 volts. This is what I'm used to from my other vehicles. The Mitchell (more for profeesional mechanics) talks about only needing 0.5 volt increases after everything is on and you run the engine up to 2000 rpm. Which one is right. If I test my wifes car it behaves like the Haynes procedure.

I'm confused, frustrated, and pulling out my hair (ain't got much left). What else should I check? Should I take the alternator back? The retailer said it's 80 amp, the original was 75 amp (I think). Is there a way to check the alternator to see what amperage it is rated for? Is it stamped on the housing somewhere?

Please help, BigDD

Reply to
BigDD
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I'd have the alternator checked. R U sure the belt isn't slipping?

Dave S(Texas)

Reply to
putt

If the belt's not loose, you have a defective on your hands. It should be able to idle at 13.5 + even with headlights and blower on. (provided the battery is at full charge when you start)

Reply to
Steve Barker

Belt is fine, no cracks and still within the tensioners limits (middle). Battery is new. I'm taking it back tomorrow to have it checked. I won't leave the store without one that has been checked first. Apparently defective off-the-self is not that unusual.

Thanks for the help. At least now I feel more confident that I know what I'm doing.

BigDD

Reply to
BigDD

Reply to
D F Bonnett

Bad alternator. Very common on the 4.9 fuel injected motor.

Been there done that. Mine is a 1993.

Reply to
gil

My replacement alternator from Autozone went bad after 6 months. Autozone replaced it free of charge. The counter guy said that I could upgrade to a more expensive alternator model and just pay the difference. The new one has been good for 4 months or so. I think moisture from underneath gets into the alternator and messes it up.

Reply to
gil

Well, I had the new alternator tested at 2 shops (Pep Boys & Advanced Auto) and it passed at both. I had the battery tested and it tested fine. Checked everything again including some things that the guy at Advanced Auto suggested and everything checked out OK.

I broke down and took the truck to my mechanic today. He called me and said the alternator was bad! I'm taking it back tomorrow with his printout and getting another one. I'm going to make them test it but I don't have alot of confidence in their tester. I'll let you know what happens.

Thanks again for all the help, BigDD

P.S. The only bright spot so far, I do know what I'm doing, the new alternator wasn't working right, and my mechanic didn't charge me for checking out the alternator.

Reply to
BigDD

most parts places like AA and AZ and PB have a basic bare-bones 'tester' that doesn't do much more than spin the unit with it full-fielded and see if the output voltage rises above 13 volts

you need a shop that has a REAL test set-up, with a carbon-pile load resistor and the ability to run it up to speed and put a real load on it, and test all the functions of the voltage regulator

the 'record' here is 4 bad units in a row from the local AutoZone for an 86 F-150.........this on a Friday evening about 8 PM in the rain

which is why I don't buy alternators or starters from them anymore

Reply to
Gary Glaenzer

|most parts places like AA and AZ and PB have a basic bare-bones 'tester' |that doesn't do much more than spin the unit with it full-fielded and see if |the output voltage rises above 13 volts

A good Mini-Tune bench tester is upwards of $1000 these days, most stores don't invest in them. Anything less is not a real tester, only a Go-NoGo machine

|the 'record' here is 4 bad units in a row from the local AutoZone for an 86 |F-150.........this on a Friday evening about 8 PM in the rain |which is why I don't buy alternators or starters from them anymore

"Worldwide" is my preferred brand. I believe it's a division of Delphi and owns the Delco Remy brand name. Reasonably priced, essentially all-new. Rex in Fort Worth

Reply to
Rex B

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