1994 2.3L 5spd over charging

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Pupfriend
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Location: Rainbow City, Alabama

1994 2.3L 5spd over charging

Postby Pupfriend » Thu Nov 28, 2019 5:47 pm

Hi, I bought a 1994 2.3L parts truck from a friend. It was missing the trans, brake mc, seat, some brake parts , shocks , etc. I’ve replaced all that stuff w/a complete driveline from another truck. It runs good. I’ve got a new battery w/12.67v showing on a Fluke MM. At idle the alternator is putting out 14.2v as you speed up the engine the voltage climbs to 17+v. I took this alternator off and put another one I had taken to a local starter/alt shop he tested it at speed and under load and it was 14.2-.4v the whole time. He said it was ok. Took the other one off it checked out good. To it across town to another shop. Same story. So, two different “good” alternators both vary voltage w/rpm when in this truck. I’ve disconnected the harness at the stud and ran a new wire from the stud to the battery + , no change. Plugged in another ign sw inside the truck & cranked it w/it. No change. Switched charge relay. No change . Any ideas?
One response on the PlanetIsuzu forum said it was the internal regulator, but what are the odds of two that check “good” being bad?
1986 SWB 5spd diesel P'up (sold)
1981 2dr Auto LS I-Mark diesel (need windshield);
198? 4dr Auto gas I-Mark (parts);
91(sold) and 94 Isuzu 2.3 p/u(daily driver);
'87 1.9L LS Pup;
A few Nissan SD22 diesel engine parts,

Pupfriend
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Posts: 451
Joined: Fri Dec 07, 2007 6:31 pm
Location: Rainbow City, Alabama

Re: 1994 2.3L 5spd over charging

Postby Pupfriend » Thu Nov 28, 2019 5:54 pm

8D39D4D7-F79E-413D-8174-AAE8FE2A0AD0.jpeg
Plug detail


Tks, Eddie in AL
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6EBD74C5-88F9-4E7C-923B-AE0C6128BC37.jpeg
1986 SWB 5spd diesel P'up (sold)
1981 2dr Auto LS I-Mark diesel (need windshield);
198? 4dr Auto gas I-Mark (parts);
91(sold) and 94 Isuzu 2.3 p/u(daily driver);
'87 1.9L LS Pup;
A few Nissan SD22 diesel engine parts,

Red Truck
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Posts: 118
Joined: Wed Sep 18, 2013 7:10 pm
Location: Vader, WA

Re: 1994 2.3L 5spd over charging

Postby Red Truck » Fri Nov 29, 2019 1:54 pm

Here's my wild guess: I don't believe an alternator should ever put out more than around 14.5 volts, but if your shop says it tests good, that's that. You say your battery is 'new', like new to the vehicle, or brand-new? I've learned that a bad cell may prompt the alt to overcharge. The battery will charge up and show 12+ volts, but discharge quickly when a load is applied, and the alternator tries to play catch-up.
'87 Isuzu pickup 2.3 gas, 5spd, 4WD

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Paul
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Location: Central Calif Coast

Re: 1994 2.3L 5spd over charging

Postby Paul » Fri Nov 29, 2019 10:03 pm

Here's a possibility. The alternator regulator has an 'remote sense' feature that helps the output voltage stay at the needed level even when there is a heavy current load. The remote sense (on the P'up) is a white/blue wire that is carried out of the regulator (through the white connector) to a connection with the B lead inside the harness. If this connection is missing it may allow the voltage to go too high.

That said, there is an internal connection inside the regulator that is supposed to take over if the remote sense connection is (somehow) missing. So, it seems that you have some issues that need to be investigated.

Also, it should be noted that running the truck with voltage as high as 17 volts will be harmful to the battery and also will dramatically shorten the life of all the incandescent lamps.

Paul
'84 P'UP 2 wd diesel, 5 spd with 0.78 fifth gear and differential back to 3.73.

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Paul
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Location: Central Calif Coast

Re: 1994 2.3L 5spd over charging

Postby Paul » Sat Nov 30, 2019 3:19 pm

Here is a schematic of the alternator circuit from the service manual that may help.

The S lead is the remote sensing lead.

Paul

Alternator schematic diagram w annotation .jpg
'84 P'UP 2 wd diesel, 5 spd with 0.78 fifth gear and differential back to 3.73.

Pupfriend
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Posts: 451
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Location: Rainbow City, Alabama

Re: 1994 2.3L 5spd over charging

Postby Pupfriend » Sun Dec 01, 2019 8:20 am

Thanks Red truck & Paul. I’ve had to work the Thanksgiving shut-down at the mill through yesterday. Someone stole my 97 Civic as I went upstairs to clock out from work. All my tools, including my ‘electrical bag’ was stolen. He was hidden watching me from woods about 100’ away. I found his bike in the woods & a drink can/candy wrapper where he had been watching. The police were pretty uninterested. The said they would send out an investigator to follow-up >= tomorrow. Looks like DNA/prints from bike wrapper etc if they match w/inside/on my car, if recovered, would be important? It came a big forecasted storm last night & probably washed away most of the evidence. I bought a couple game cams to watch the bike....
1986 SWB 5spd diesel P'up (sold)
1981 2dr Auto LS I-Mark diesel (need windshield);
198? 4dr Auto gas I-Mark (parts);
91(sold) and 94 Isuzu 2.3 p/u(daily driver);
'87 1.9L LS Pup;
A few Nissan SD22 diesel engine parts,

Pupfriend
Regular Member
Posts: 451
Joined: Fri Dec 07, 2007 6:31 pm
Location: Rainbow City, Alabama

Re: 1994 2.3L 5spd over charging

Postby Pupfriend » Sun Dec 01, 2019 8:37 am

Sorry I got off-topic. Bought $150 worth of HF tools to get me by. Had 6 bags of tools in car w/some M18 Fuel & 20v impact. Worse thing is eyeglasses, coat shoes, some of my passed dad’s tools, etc.
Paul: The diagram was especially helpful & your best estimates
of what was wrong. When I run it, I have the new headlights on bright to soak up some voltage. They keeps it in the 14-16v range.
Red Truck: the battery is brand new, albeit a blem from InterState. No problems w/it cranking, discharging down w/accompanying slow starts. I will remove it and run it up to Advance/OReilly’s for a check out, though. Weird that two diff shop-tested alternators have the same results, otherwise I would off-the-cuff think it would be the internal regulator.
1986 SWB 5spd diesel P'up (sold)
1981 2dr Auto LS I-Mark diesel (need windshield);
198? 4dr Auto gas I-Mark (parts);
91(sold) and 94 Isuzu 2.3 p/u(daily driver);
'87 1.9L LS Pup;
A few Nissan SD22 diesel engine parts,

Pupfriend
Regular Member
Posts: 451
Joined: Fri Dec 07, 2007 6:31 pm
Location: Rainbow City, Alabama

Re: 1994 2.3L 5spd over charging

Postby Pupfriend » Sun Dec 01, 2019 11:00 am

Red Truck was right. Initial voltage on new blem battery was just over 12v. After 10 min on O’Reilly’s machine it dropped to 11.9v
They said the initial reading was prob “surface charge” on the plates and it would drop to what the charge the battery was actually after a load was applied, echoing essentially what you were saying. After over an hour on their machine. It quits & prints out “bad battery, bad cell”. Get home, put another ‘green dot-type’ battery in (dot green) cranks right up, 14.2-4v idle, increases proportionally w/throttle to 18v (would prob go higher WOT). Now we’re back in Paul’s court....
There’s probably some nested problems going on here...
1986 SWB 5spd diesel P'up (sold)
1981 2dr Auto LS I-Mark diesel (need windshield);
198? 4dr Auto gas I-Mark (parts);
91(sold) and 94 Isuzu 2.3 p/u(daily driver);
'87 1.9L LS Pup;
A few Nissan SD22 diesel engine parts,

Pupfriend
Regular Member
Posts: 451
Joined: Fri Dec 07, 2007 6:31 pm
Location: Rainbow City, Alabama

Re: 1994 2.3L 5spd over charging

Postby Pupfriend » Sun Dec 01, 2019 7:07 pm

Turns out it was 2 alternators in a row that we’re bad.
Put a third alternator on and it is charging just fine now....
1986 SWB 5spd diesel P'up (sold)
1981 2dr Auto LS I-Mark diesel (need windshield);
198? 4dr Auto gas I-Mark (parts);
91(sold) and 94 Isuzu 2.3 p/u(daily driver);
'87 1.9L LS Pup;
A few Nissan SD22 diesel engine parts,