Bad alternator
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Bad alternator
so I have an 89 250 7.3 idi my voltage on my dash read 8 volts I replaced both batteries cause they were both bad but now I'm reading 9 bolts before I turn the key to crank and when I start it up it drops to 8 and is slow to crank then when running it jumps back to 9v and stays there in thinking it's a bad alternator I don't know how old it is it was on there when i bought the truck
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ok thanks a lot
Cargo Master
Joined: Oct 2012
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From: California
whoa whoa whoa.
A.) I can't remember if the 1989 had a voltage regulator, but if it does, then replace that first.
2.) bring your alternator into an Autozoo or similar parts store and have it tested.
d.) if your alternator is faulty, you don't have to buy new. Look in your yellow pages for an alternator shop. They can rebuild it much cheaper.
III.) did you have your batteries tested before you replaced them? Your alternator might not have been charging them, and they could have been fine.
7.) Don't just by a 160-amp alternator. IIRC, that's the ambulance alternator and it won't have the right connections or wiring for your truck.
IV.) What do your cables and terminals look like?
A.) I can't remember if the 1989 had a voltage regulator, but if it does, then replace that first.
2.) bring your alternator into an Autozoo or similar parts store and have it tested.
d.) if your alternator is faulty, you don't have to buy new. Look in your yellow pages for an alternator shop. They can rebuild it much cheaper.
III.) did you have your batteries tested before you replaced them? Your alternator might not have been charging them, and they could have been fine.
7.) Don't just by a 160-amp alternator. IIRC, that's the ambulance alternator and it won't have the right connections or wiring for your truck.
IV.) What do your cables and terminals look like?
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Freshman User
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I had the batteries test and they were no good so I swapped them out and now I'm reading 9 volts sounds like the alternator is not charging them I used this truck everyday to go to work so it's been starting but takes a while probably cause it's just using the batteries to start it
Postmaster
Joined: Oct 2014
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From: Thomaston
Now would be a good time to upgrade to a 3g. There are several threads on it here and other forums. Using a junkyard alternator it about a 50.00 conversion. The purpose of the alternator is to recharge the batteries. When you put the fresh batteries 8n did it spin over fast or was it slow? If it still spun slow then it is either cables or the starting system. If it spun fast but is getting slower then it is a charging problem and you are killing your new batteries.
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Fleet Mechanic
Joined: Oct 2012
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1. Charge the a batteries all the way up and try and start it. With freshly charged batteries it should turn over fast. The lowest my cab voltage gauge goes is 10.8ish in the winter when the GPs are on or I am actively cranking the engine. This is measuing the voltage with at the 12v outlet, not at the batteries.
2. 9 volts running is low on new batteries, even with no alternator. I would suggest replacing the positive battery cable, cleaning all your grounds and insuring that the connections at the battery are good/clean.
2. If the alternator is bad, upgrade to a g3. There are how to threads on the forum with pictures.
2. 9 volts running is low on new batteries, even with no alternator. I would suggest replacing the positive battery cable, cleaning all your grounds and insuring that the connections at the battery are good/clean.
2. If the alternator is bad, upgrade to a g3. There are how to threads on the forum with pictures.
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1. Charge the a batteries all the way up and try and start it. With freshly charged batteries it should turn over fast. The lowest my cab voltage gauge goes is 10.8ish in the winter when the GPs are on or I am actively cranking the engine. This is measuing the voltage with at the 12v outlet, not at the batteries.
2. 9 volts running is low on new batteries, even with no alternator. I would suggest replacing the positive battery cable, cleaning all your grounds and insuring that the connections at the battery are good/clean.
2. If the alternator is bad, upgrade to a g3. There are how to threads on the forum with pictures.
2. 9 volts running is low on new batteries, even with no alternator. I would suggest replacing the positive battery cable, cleaning all your grounds and insuring that the connections at the battery are good/clean.
2. If the alternator is bad, upgrade to a g3. There are how to threads on the forum with pictures.
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Freshman User
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ok guys I replaced the alternator now my volts on the dash is reading 13 at idle when I give it gas it stays the same when I cut everything on like ac and the lights I get between 11 and 12 volts is that good every thing works on the dash except fuel gauge and speedometer what could that be fuses maybe bad fuel sending unit
Posting Guru
Joined: May 2015
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ok guys I replaced the alternator now my volts on the dash is reading 13 at idle when I give it gas it stays the same when I cut everything on like ac and the lights I get between 11 and 12 volts is that good every thing works on the dash except fuel gauge and speedometer what could that be fuses maybe bad fuel sending unit
Just out of curiosity what size alternator did you buy? Was it big like the old one or smaller?
Fleet Mechanic
Joined: Oct 2012
Posts: 1,943
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Mine could be a little different because it is a van with an extra blower in the back.
If the OP is worried, it is always a good idea to make sure all the cables are in good order and the grounds are clean/tight.
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