2nd Gen Non-Engine/Transmission Alternator/regulator questions

[Bill Lins]

Yesterday morning, I noticed my voltmeter reading 11-12 volts instead of the normal 14+. When I got to work, I checked under the hood & found the negative cable on the passenger-side battery to be extremely loose. I tightened it but the voltmeter still reads low. How do I determine if the alternator, regulator, or something else is the problem?

My truck is a '98 2500 QC, 12 valve engine & 5-speed trans.

 

[phantomusa]

Put a volt meter on your battery and run engine at about 1200 rpm the voltage should read 13.5-14.5 volts
Or just take your truck to a auto store they can check it for you

 

[GAmes]

Check the big fuse (I think it is 40 amp) that is in the PDC. The big alternator wire goes to one side, the other goes to the battery.

 

[Bill Lins]

Check the big fuse (I think it is 40 amp) that is in the PDC. The big alternator wire goes to one side, the other goes to the battery.

Fuse looks OK, thanks.

 

[Bill Lins]

Put a volt meter on your battery and run engine at about 1200 rpm the voltage should read 13.5-14.5 volts

My meter is @ work so I'll try that tomorrow. Should I put the meter's negative lead on the battery's negative terminal or on a ground elsewhere under the hood?

Further, do I understand correctly that, if the alternator checks out OK, the problem must be the regulator by elimination? Or is there a way to test the regulator?

 

[Wayne M.]

I don't know the 2 gens too well, but AFAIK, the regulator is built into the PCM/ ECM. The computer controls the field. Have you checked the voltage at the Bat lug on the alternator itself?

 

[GAmes]

Bill, removing the alternator and getting it tested at a place like auto zone is the easiest way to find out if the alternator has died. I'm not saying to get a replacement there, but they will test them for free. If the alternator checks out then the PCM voltage regulator has failed. Wiring in an external voltage regulator is a simple job and not very expensive. Finding a PCM for a '98 will be very difficult. If an external regulator is the solution I'll be happy to pass on the wiring info.

 

[DavidC]

Does the 98 12 valve have the sensor under the Drivers side Battery like the later Models ?. If it does it also controls charging to some extent. Just throwing this in the mix.

Dave

 

[GAmes]

Does the 98 12 valve have the sensor under the Drivers side Battery like the later Models ?. If it does it also controls charging to some extent. Just throwing this in the mix.

Dave

Excellent point, glad you brought it up. The FSM lists the specs for testing the battery temp sensor. They can and will cause a alternator to not charge. Mine failed several years ago along with my PCM regulator. I don't know which failed first, but replacing the PCM didn't fix the problem until replacing the sensor. The AutoZone replacement has worked well for a few hundred thousand miles.

 

[Bill Lins]

Thanks for all the tips. I didn't get to do much today- seems my multimeter grew feet & either left the area or is playing hide & seek.
May have to pick up another one tomorrow & keep it locked up in the truck.

 

[Bill Lins]

If an external regulator is the solution I'll be happy to pass on the wiring info.

I sent you a PM.

 

[Missouri Mule]

Usually if the battery temp sensor goes it won't charge at all.
ESS turns on the asd relay which sends line voltage to evr.
I would get both batteries tested. Your passenger side battery terminal being loose it probably was not being charged.
Drivers side could be a little low too.
I put a voltmeter on battery (s) to see what their volts are engine off. Then I get engine started and see what the volts are. You should be able to tell if alt is working.

 

[Bill Lins]

I put a charger on the batteries for all day Sunday. Guess I should have checked them first. The truck still starts but I'll probably have to put the charger on it again before I get it sorted out.

 

[K5IP]

Be sure your tach is working. If it is also inoperative look for a bad engine speed sensor (ESS).
Rog

 

[Bill Lins]

Tach's working OK. I ordered the Denso rebuild kit from Geno's. If it turns out to be the regulator, has anyone any experience with the internal regulator kit LarryB's offers or is the add-on external regulator the best way to go?

 

[LandShark]

External is easy to do. I did this to get by when my PCM when out and was waiting for a new one.

Get a generic version of this from any auto parts place.