Ok, so today I got another alternator. I checked the ground and all was good. Checked it in MANY places and was 12.73 volts everywhere while the vehicle was off. Started the vehicle, voltage dropped to 12.29 volts and stayed there, rev the motor and the voltage drops the more you rev it... let off the gas returned to exactly 12.29 volts. Tachometer still not working stuck between 0 and 500 rpms... so I start troubleshooting before this alternator goes bad too... On the post of the top bolt on the alt I had 12.29 volts, on the middle post I had 11.84 volts and that wire has voltage on it when it was unhooked from the alternator and the post itself has none... I assume that is the exciter? On the bottom post there is less than 5 volts (roams between 1 and 5) When I unhooked the battery to see if the car would still run on just the alternator it did but poorly. Idled at about 500 rpm and if you try to throttle it up it would surge up for a second then bottom back out then surge up again and bottom out etc etc, also there was only about 7.75 volts coming from the alt with the battery unhooked. Continuing with the troubleshooting I ran it on just the battery... ran fine throttled up fine... heres where I get really confused. With the alt unhooked from the elec system there would be just 2.5 volts at the top post... and only about 2.4 at the second post... BUT THE RPM GAUGE WORKS FINE!!! of you put load back on the top post the rattiling scraping sound starts again and the rpm gauge resumes being stuck at 250ish. I ran the vehicle at idle for 3 hours... the voltage never left the 12.27 to 12.29 range. I tried systematically removing each fuse on at a time to see if there was a short... no change. I unhooked the starter while the vehicle was running( so the starter isnt shorted) the only fuses I could not properly check were the fuel and ignition system fuses... Hoe does the ignition system ground? Is there a chance that the lead that feeds the ignition is shorting? What leads me to think this, is how the car runs when the battery is unhooked. If when the idle goes up and the system attempts to produce more voltage it is shorting in the ignition system when it revs and pulls all the voltage off the system until it almost dies... ceases to short and starts the cycle over again.. Up to now I have replaced the plugs, wires, 4 alternators, battery, coil packs, and double checked and double cleaned all the main grounds.


PLEASE HELP!!!

 

Source for this alternator?

 

Pull fuse F14 under dash. That should drop power to the smaller of the two bolt on leads (exciter). Would like to know if truck can crank and run on battery alone. Recheck belt route one more time. Large bolt on lead goes thru 100 amp main fuse link to truck and battery. Should read almost identical volts to chassis from (+) battery lead and big bolt on back of alternator. This alternator does not sound like it would pass the test at the parts store.

 

Also attach a battery jumper cable from alternator frame to (-) battery, in case engine to frame bond is suspect.

 

Tested the alternator before putting it on rover. Pulled from a 98 range rover with 76000 miles. Top bolt lead does run to the 100 amp fusible link, belt routing is correct, have tried using many jumpers and extra grounds with no change. Tested voltage several times at many ground points all read identical to negative post on battery... voltage on top post on alt is identical to the pos terminal on battery 12.29 volts while running... Identical results on 3 morelli magnets alts... only one that behaved differently was my bosch alt... it still charges the rig at 13.75 volts while running but has a 2 volt draw when not running killing the battery in a matter of 40 or 50 minutes which means the diodes went out... the truck is eating alternators for lunch at this point and its getting expensive throwing alternators at it to try troubleshooting it more. The only thing I havent done is load test the battery... but this problem started back in November and originally came on slow and one of the first things I did was buy a brand new Interstate battery... so its only 3 months old.... I feel like if nobody on here can help me then taking it to a shop is going to be just as useless and they would just start by replacing all the things ive already replaced and rack up an insane bill troubleshooting this... Im at my wits end and feel like I may end up just parting it out over a frickin charging issue. Cant think of anything else to try... I probed around on it for 3 hours today while it was running trying to find something out of spec or irregular that could explain it... I charges just well enough to keep it running at idle... but if I rev it at all the voltage starts to drop... and if I even put the fan or wipers on the voltage drops enough to no longer charge... Still open to any new ideas... or if you know a reputable shop in the Seattle tacoma washington area that I could take it to that wouldnt need 20 hours at 120 an hour to find whats wrong

 

In no particular order -

1. Any access to a friend with a clamp on DC amp meter? MAkes it easier to see how much drain at what point. As an example, my stock D1 draws 85 amps from alternator with everything switched on and at idle.

2. With alternator off line (top bolt disconnected if you like), will truck crank and run on battery alone, and when running what is the voltage across the battery? Battery could have developed problems with all the other issues going on. Age of battery does not matter at this point. If battery won't hold a charge, and keep load up without dropping volts like a stone, then that is one part of problem.

3. When you say you removed fuses while it was running, trying to isolate an excessive load (ground), did you also take out fuse links in the underhood box? Some fuse links and fuses in that box feed other groups of fuses, some feed major load device.

4. Without truck cranked, but key turned all the way to position where oil pressure and other warning lights come on, what does battery volts do? In other words, does the high current drain happen when switched on, or only once it is cranked and engine running? If something strange with starter wiring.... perhaps a way to isolate that in the "not-running test" would be to take off the battery wires on the plus terminal. And separate the short wire that goes from (+) terminal to fuse box. It is small, the large (+) terminal wire goes to the starter (with no fuse). Attach small wire back to batttey, but not big cable that goes to starter.

5. So what I am suggesting is testing system with battery only, and big wire to starter taken off battery (use small wire only that runs to fuse box). You could also meter for ohms on the big (+) cable, disconnected from battery, to frame. Should read open, because solenoid has to pull in to connect starter positive to starter windings. Can also do similar test for fuse box to alternator wire (ohms to ground with wire off the bolt on the alternator).

6. You could be looking at a "rub" (rubbed on a piece of metal and worn insulation) or skint place in the wire groundiing the system out and placing a big load on the alternator. This bad place in the wire could be anywhere from (+) battery to starter, or big bolt on alternator to fuse box. Might be other places but you start running out of large cables that don't have fuses. Unless truck modded by aftermarket add-ons.

7. Who tested alternator? If done by a parts store, try another store. Sometimes behind the counter techs or their equipment can produce different readings. Your symptoms indicate a bad regulator and some open diodes on the alternator. Volts low, and volts drop when moderate extra load switched on.

8. Wire on back of alternator pretty simple - big one goes to fuse box, middle sized one goes to the "volts when ignition switched on and battery warning light on dash" circuit (battery light does come on before truck cranks?). Very small wire with push on lead is the drive signal (pulses) to the tach.

 

ummm ... any chance the two terminals in the front of the under hood fuse box need to be cleaned and tightened? And for long life issues, any overheating, or is your radiator fan blowing air toward the engine block (radiator cowl directs that air flow into alternator, if rad fan was on backwards, not good).

 

Ok heres an update... Took all 3 marelli magnets alts down to the auto zone and to pep boys and had them tested... all 3 of them are still good and so is the battery... So it wasnt my alternator getting worse slowly it is something else. I can guarantee I have ruled out the MAJOR grounds ( bat to body, body to frame, frame to block) all 3 alts ran on the bench between 14.3 and 14.6 volts but on the car I cant get them above 12.3. For the life of me I cant find an electric diagram for the 97, 98 GEMS ignition system. The rave only has 95, 96 and the D2 doesnt have an elec diagram. I want to trace all my idnition wires as I think this is where the problem is spawning from. Or can someone tell me where to run jumper wires too to bypass the current ignition wiring and feed it with current direct to verify if there is a short somewhere? Also to answer Savannah yes it runs and cranks fine on just the battery... it revs fine as well and no abnormally fast drain of the bat either

 

OK, in my signature is an on-line source that allows you to view on line at the 1997 electrical troubleshooting guide, which would be for the GEMS engine.

1. If you have digital volt meter, and fully charged battery; install battery but don't connect.

A. Read battery volts with nothing attached. Assume 12.6 - 13.0. Disconnect wire at hood alarm switch (driver side).

B. Connect cables. Read battery volts - should not have drop very much if at all, because only load would be clock, security, ECU, radio memory, etc.

C. Switch on ignition, but don't crank. Battery may drop quite a bit, if you have a stray drain in there. Unplug fuses or fuse links to isolate.

D. You have something somewhere that is a serious drain, OR the smaller of the two large wires on back of alternator is not supplying enough voltage to make the alternator function. The big wire is the alternator output. The tiny wire that plugs on is the drive for the tach. The other wire that bolts on is from the battery light on the dash. Does that light come on before crank, and go out afterward?

E. I don't have the exact volts at hand, but in a couple of hours I'll be back at my shade tree and can tell you the exact readings I have. If that wire was not right, would allow alternator to bench test, but not work right in the truck. The amount of extra drain would have to be in the 100 amp range because a full load on a stock D1 is only like 80 amps or so. Hard to miss that.

 

OK, my D1 has been under the shade tree for over 24 hours. Here's my voltages:

Key off - battery = 12.78 ; alternator output 12.78 ; altenator other wire - 0 volts

key on - battery = 12.41 ; alternator output 12.38 ; alternator other wire 1.05 volts

running at 700 rpm idle - battery 14.13; alternator output 14.21 ; alternator other wire 13.60.

Nothing other than basic stuff running, dome light, no AC, no head lights.
Clamp on amp meter measured 17.9 - 18.2 amps from alternator, 2.3 - 2.5 of that going into battery.

The main cable is brown, and goes on top bolt, then over to underhood fusebox (100 amp fuse link). The smaller cable is brown & yellow, goes on next bolt down. This one should be closely checked with meter. The "flying lead" that plugs in goes to tachometer and can be disconnected for these tests.

Your meter - have you checked it against another vehicle?

What volts does you battery have when nothing on, key off? With key on, but not cranked? Do you see it increase once cranked? Just me, but 12.3 seems way low.