The alternator voltage regulator inside the engine controller seems to have gone south (actually, it is intermittently working). I wired up an external voltage regulator that seems to be the go to method for older vehicles such as this since engine controllers for the B350 are almost impossible to find.

Initially everything worked great. I wired in a 194 bulb to the existing field terminal wires to keep the Check Engine light off and that appeared to work. However, the past few days, the morning temperature has dropped (48F) and when I started the van the Check Engine light would come on. After a short warm-up and restart, the Check Engine light remains off. System is charging (according to the voltmeter) so no issues there. I figured the engine controller circuit monitoring the factory field wires was not happy with the 194 bulb load based on the operating temperature and/or voltage it was monitoring from the external regulator.

I tried a few different bulbs with different wattages to simulate different loads for the field current. I have a 97 bulb in there now and his morning (48F) the Check Engine light did not come on. There may be an optimum current that the field can operate at under most conditions (external regulator) to keep the Check Engine light off. Of course charging the battery is the most important issue, but I like to keep lights off and circuits working if possible when modifying things.

Hope this helps another member. Info like this is sparse out there.

Nick

 

You need to read codes, and see what the computer is whining about. What year is your van?

 

B350, 1991.

Looks like codes 41, 46 and 47 are stored.

 

Well, those all relate to the charging system...... What happens if you leave the computer hooked up as well as the external regulator? (47 is battery voltage low......)

 

Computer is still connected because the engine is TBI.

The OE field terminal wires (from engine controller) are connected to the 97 bulb. The field terminal wires from alternator are going to external regulator.

 

Put the OE field terminal wires on the alt as well. (from the pcm.) see if anything changes. Since it wasn't working anyway...... shouldn't hurt anything, and it *may* keep the computer happy..... If it doesn't, like gonna have to either live with the check engine lite, or replace the PCM.

 

I revised my initial description... the built-in voltage regulator is intermittent, so it is not totally dead.

Just thought I would share that different wattage bulbs wired to the OE field terminal wires will give different results under certain conditions if you want to try and keep your Check Engine light off and not just disconnect it or ignore it.

Thanks for the replies though.

 

Why did you use a bulb instead of a resistor? IF that keeps the light out measure the resistance of the field on the alternator and get resistor with the same resistance.

 

The resistance of the rotor field coil is 1 ohm or less. Unless the alternator has an extremely heavy load demand, the field coil is not fully excited. Using a 1 ohm (or less) resistor would draw about 14 amps, not a good idea nor it is necessary. In addition, this resistor and power rating would be HUGE.

As long as the computer sees that there is some field excitation going on, the Check Engine light will usually stay off most times.