Chrysler Repair: 96 Van: IOD resistor causes rough engine running, amp fuses, postal mail

Question
Hi Roland, I have a 1996 chrysler town & country (grand).
Some time ago the battery was replaced, after that the radio did not remember stations, interior lights did not come on when opening the doors,etc. I found out finally that the iod fuse had popped. After replacing it, everything worked fine except for the engine, it became rough, as if misfiring. removing the fuse cures the roughness, but leaves me with the mentioned problems.
can you tell me how to solve this? thx for your time in advance. With regards Rob Hoogsteen (netherlands)


Answer
Hi Rob,
That is an interesting behavior. First I need to clarify which resistor exactly when taken out causes the improvement. I have a '95 and a '98 manual; I believe the '95 is more like your '96. In that manual the power distribution center under the hood is shown to have eight 15 amp fuses of which the A is labelled IOD. Is that how your van is set-up? Let me know and we can then proceed to analyze what is going on.
I suspect that some component on that circuit is defective and when it is powered up it impacts the engine control system, but I can't be sure how that is happening except that the engine computer shares the voltage supply circuit also used by the IOD resistor. Maybe some transient noise is entering the power supply and raising havoc with the computer. The current flow through the IOD is supposed to be around 30 mA when everything is shutdown. That is needed to maintain some of the solid state memory devices like that in you radio. And the fact that the IOD fuse blew once suggests that something it feeds is shorted to ground intermittently. The manual suggests reading the current flow through the IOD circuit (by measuring the battery current again with everything is off) but you have to either have a meter that is capable of reading amperes or use a test bulb to protect a mA meter if you use that approach. It may be best for me to send you that procedure by xerox copy and postal mail because it is too lengthy to type in here. But first lets make sure I have the correct wiring diagrams that apply to your van.
You might want to see if you can get any fault codes from the memory of the engine computer. Try the ignition key: on-off-on-off-on and leave on, doing that in 5 seconds elapsed time or less. Then watch the check engine light which remains on to begin to flash, pause, flash, etc. Count the number of flashes before each pause. Then repeat to verify the counts. Group the counts in pairs to form the two digit fault numbers. Let me know what numbers you get. '96 was right on the edge of the OBD-I and OBD-II changeover, so this may not work as a readout tecnique. But give it a try.
Roland