On my 93 my alt isnt charging the gauge inside the cab was reading 11 then 10 then it dropped to 8, so i swapped a alt with another one of our trucks and i got the same results, then i swapped in another alt from a 97 12 valve, and it is staying at a steady 11.8 volts at the alternator. does anyone have any ideas what is wrong

 

Do a load test on the battery. If it has a bad cell you can get the same results...check the grounds too.

 

ive put two other batterys in the truck also i checked the groung going from the alt to the block also

 

Might be the stupid computer.

 

Check the crank sensor and its wiring.

 

Could you elaborate on this? What is the crank sensors role in the process of charging?

 

The crank speed sensor tells the computer the engine is running, and rapidly grounds the fields in the alt. If the computer doesn't know the engine is running it won't charge.

 

Somewhere around 91.5 some genius or more likely a committee of them at mopar thought it'd be cool to let the computer act as the voltage regulator.
If it doesn't sense rpm's (via the crank sensor and it's wiring) it won't tell the alternator to charge.

 

how would i check the crank sensor and its wiring

 

Smoke' Em, look through the 'sticky'. there is a very informative article about having a alt rebuilder install a kit to bypass/eliminate the PCM's role in charging. The guy by me was so impressed with the article, he ordered 4 kits. One is for my dad's truck. Hope this helps,

 

Also in the sticky look at the one on trouble codes.
See if your truck is setting the code for high or low voltage or the crank speed sensor during cranking https://www.dieseltruckresource.com/...58#post1107258

 

i dont have any trouble codes

 

The crank sensor usually won't set a trouble code - because the PCM doesn't know the engine is running so it's not looking for a signal.

Most times the trouble is worn out insulation on the wiring to the sensor. The other thing that happens is that the mounting nuts loosen and the sensor falls down against the damper and gets worn out.

It really is a Rube Goldberg setup, but Chrysler products used the PCM to run the alternator from the early '80's on. The CTD's were the last holdouts with a separate regulator after the rest of trucks went to electronic fuel injection in the late '80's. It's only troublesome on our trucks because of the silly method they used to signal the PCM that the engine was running. An oil pressure switch would have been simpler, cheaper, more durable, and just as effective.

 

ok so i put in a crank sensor off of another parts truck that i got, i now have some trouble codes and ive tried repeatadly to get the codes but im having a hard time getting the blinks down, are there any tricks

 

Nope, just count blinks. There's a short pause between each digit, and a longer pause between codes.