Testing an IDM?

[oxbrain]

My car('91 on stock ignition, harness, and ecu) is throwing a code 01. Check distributor wiring to IDM. I have a spare ignition module that I thought was good, threw it on, same thing. I don't have an easy way to get another IDM, and any new replacement is at least a week out. Is there any way I can test the modules I have to see if they work?

From what I understand, when the IDM gets a signal from the ecu(pin1) it connects ground(pin2) and coil(pin3). Is that signal + or -, or is it some kind of wave? Does it function like a relay where it stays grounded as long as the signal is present, or does it only instant connect to trip the coil?

Would installing a MSD ignition system bypass this problem and what's the easiest tach signal to use with it?

[FB71]

uh, IDM stand for Ignition Diagnostic Monitor... the hardware is the tach wire back to the PCM from the coil. IDM is just a piece of software in the PCM that monitors coil function via the tach wire.

[oxbrain]

Ya, I was confused because I wasn't finding it anywhere else in the book. Other posts here say the IDM is the ignition module so I went with that.

I can't find anything in alldata about the pcm getting any rpm signal back from the coil. It's got a crank sensor in the distributor and drive the coil with that. Chiltons mentions a RPM data link connector, but I can't find any other reference to it. The tach does jump around when I crank, just no spark.

This has been a confusing issue overall. So far I've replaced every part in the ignition system including the ecu, and chased every wire from the distributor and ignition module and found no shorts and get the same code. My original response was to just park the car until I get the megasquirt going, but I need this running asap before my brat dies.

[WmWatt]

Some auto parts stores test ignition control modules for free. For some I gathered look in http://www.ag384bn.bravehost.com/Cars.htm

[oxbrain]

None of the parts stores in the area seem to have a tester.

I hit the junkyard and grabbed 4 other modules, all give me the same 01 code and no spark. This is getting very frustrating.

Distributor - Checked OK, swapped with known good
ECU - Swapped with known good
Coil - Tested OK, swapped with known good
Ignition module - Swapped between 6 in unknown condition, unlikely all are dead
Wiring - Continuity on all wiring according to alldata

Any ideas?

[oxbrain]

Problem found. I guess replacing the module fixed the no spark, but the car still wasn't starting. Apparently the timing belt slipped nearly 1/4 turn on the crank pulley while being fully tensioned and not slipping at all on either cam pulley and not causing any damage to the belt. If it had slipped a tooth or two it would still be sputtering and I would have checked the timing belt closer.

Angry that I didn't notice sooner, but at least now I know what to fix.