1996 Trooper 5 Speed 3.2 SOHC

At idle the output is great but as throttle and/or load are applied the output drops to 12v or a bit less. When you let out of the throttle to coast the voltage comes back.

It manages to keep the battery charged and has never stranded me but I am worried about it. My 1995 Automatic has enver done anything like this.

I'm going to take it in to an alternator shop but wondered if others had seen this behavior.

Mark

When mine went out the output was "great" also. Too great, actually. I'm surprised your auto tranny hasn't been acting up, that was the first symptom that mine was going bad, the battery never died or anything. Get it tested while on the vehicle.

Airtight,

Thanks for the reply. The one that is having the issue is on a manual transmission. I've already pulled it (easy enough to do) and figured at 145,000 miles it could use refreshing <img src="/forums/images/graemlins/smile.gif" alt="" />

vanduker,

My '96 has done that as long as I've owned it (since 1997 with 20k miles) and I have 145K miles. Only in the last couple of weeks have I began to have alternator issues along the lines of what Airtight is talking about (tranny acting up).

Just back fromt he alternator shop where the guy bench tested it under load and thought it looked great. His thought was that it could be a slipping belt or a bad battery.

I doubt the belt is slipping as I have had to deal with that before. On mine it would squeek soemthing awful on startup until I got it tight enough.

I do wonder though about the battery. When the throttle is applied the voltage immediately goes way down - from ~ 14.5v to ~ 12v. I would think even if I pulled the alternator off line with the vehicle running it should start at 13.8v and then go down a bit at a time.

The battery starts the truck fine but then again the motor is tiny and the compression is low.

I've had GM cars that would start fine but the computer would show a fault with the charging system and the fix was changing the battery.

Any other opinions?

Mark

The alternator is designed to drop it's voltage under load, it says so in the owners manual. My Isuzu's have always done that. You should have had the guy replace the brushes while the alternator was out and you would have been set again for years.

Yup.
A simple test to see if it's working properly is to turn on the headlights. With the headlights on voltage should remain ~14V regardless of what you are doing with the throttle.

Another Idea is to check the engine relay. I had Jerry Lemond test my engine relay and it was bad along with my alt. Mabe Jerry can chime in on how to test it.

Dylan.

SOUNDS LIKE THE ALT IS DOING WHAT IT IS SUPPOSSED TO ON THESES VEH, THEY DO OPERATE DIFF THAN WHAT WE ARE GENERALLY USED TO , ONE WAY TO GET A PRETTY GOOD IDEA IS TURN ON THE HEADLITE ENG OFF WITH A VOLTMETER HOOKED TO THE BATT, LEAVE THE HD LITES ON FOR A COUPLE OF MINUTES TO PUT A DRAIN ON THE BATT, NOW START THE ENG AND WATCH THE V/M IT SHOULD GO PRETTY QUICK TO OVER 14 VOLTS OR AT LEAST 13.5 AND KEEP CLIMBING TO AROUND 14.2 AFTER IT SETTLES DOWN NOW TURN ON THE A.C WITH ALL THE LITES ON FOR A FULL ELECTRICAL LOAD ,IF THE ALT KEEPS THE BATT VOLT TO AT LEAST 13.8 AT JUST ABOVE IDEL SPD YOU DON,T HAVE AN ALT PROB, ,YOU COULD ALLSO WIRE IN AN AMMETER AN D ACTUALLY CHECK THE CHARGING CURRENT TO SEE WHAT THE ALT IS REALLY PUTTING OUT AS FAR AS THE FULL CURRENT CAPABILITY BUT IT GETS A LITTLE MORE INVOLVED , IF YOU HAVE A LARGE FULLY (HOT )CHARGED BATT THE ALT MAY ALLSO NOT THROW A FULL 14 VOLT OR SO UNTILL THE BATT IS DRAWN DOWN A LITTLE BIT .JERRY

Jerry,

As long as I don't run the rear window defroster at just above idle and steady state throttle it will maintain 13.8 or so.

Upon application of any throttle the voltage immediately drops but will come back up as the engine maintains the higher (but constant) RPM.

Application of full throttle even with no load (flicking the throttle by hand) can cause the voltage at the battery and alternator to get to just over 12v.

I've measured the voltage at both the battery and alternator and there is at most a couple of tenths of voltage difference.

Maybe that just the way these are, but my 95 automatic one doesn't behave this way - you can floor the throttle all day with no drop in voltage.