800 milliamps is of course way too much but so is 85 ma. The problem is some of the computers need about 20 minutes to go to "sleep mode". Until then, they could draw up to three amps. This is when the Engine Computer performs some self-tests on emissions components. By 20 minutes it knows you're not just stopping for gas. Once in sleep mode the current drain must be less than 35 ma.
Anytime you open the circuit the computers wake up again and start counting all over. The circuit is opened to insert your ammeter, AND it is opened momentarily when switching the range on your ammeter. Many digital VOMs have a 2 amp scale and a ten amp scale that requires moving the positive meter lead to a different jack. Most meters have a 2 amp fuse to protect the lower ranges but the ten amp jack is not fused or is at least large enough to allow measuring that three amps the computers could draw. You may need to start out on the ten amp scale then wait for the computers to time out, but then there isn't enough accuracy after the decimal point, so you have to switch to a lower scale. Moving the meter lead opens the circuit, the computers wake up when the lead is reconnected, and the two amp fuse blows. The fuse isn't the problem in your van since the computers are only drawing.8 amps. Still, after the computers go to sleep, you might want to switch to a lower scale for more accuracy. Meter range switches are called "break-before-make" switches meaning one range turns off before the next one turns on. Two different switch contacts are never in contact at the same time. Simply switching to a lower range opens the circuit and causes the computers to wake up again.
To solve these problems, disconnect the negative battery cable, then place a jumper wire between the cable and battery post. Connect the meter across that jumper wire. You can start out on the lower range because all current will be flowing through the jumper wire. After half an hour, disconnect one end of the jumper wire. Now current will flow through the meter and the circuit was not broken. The computers will stay in sleep mode. If you want to change the range, simply reconnect the jumper wire first, change the scale, then remove one end of the jumper again.
Wednesday, February 9th, 2011 AT 7:16 PM