DIY '89-'95 S4/GT/GTS Bypass Bridge for Ignition Control Module
 

I don't recommend bypassing the Ignition Control Module on cars equipped with catalytic converter exhaust systems, however for testing purposes, I made the bridge shown in the wiring diagram below, from a commonly available 12V SPDT automotive relay.

http://img188.imageshack.us/img188/1873/icmdiagram.jpg

The Ignition Control Module can be problematic if the the exhaust temperature sensors (thermo elements) are not working properly.

You can buy a bypass Bridge from Porsche (part # 928.615.175.00) for about $25 plus shipping.

12V SPDT relays, commonly used on aftermarket alarms, are available in most automotive supply stores for a few bucks.

Here's a few photos of the modified relay. Two pins must be broken off at the relay base. Inside the relay, I removed the relay coil and pivot contact, soldered the remaining pins together electrically with a length of solid strand wire.

http://img42.imageshack.us/img42/8713/icmbipass003.jpg

http://img42.imageshack.us/img42/476/icmbipass005.jpg

http://img188.imageshack.us/img188/9...mbipass006.jpg

BUMP: not sure what was done here or why, but researching modules after a suggestion was made in my thread about voltage drop.
anyone want to explain this single post from nearly 10 years ago?

Pictures are not showing up for me, anybody else?

Borland took a common 53B relay, removed the guts, and tied three pins togeether with jumpers inside the can to make his own bypass plug-in.

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While many report that the relay or the thermocouples have failed, the most common cause of problems traced to the system is faulting combustion in a measured cylinder. It may not be a fill ignition fault on one system (coil/distributor) that the original system is intended to protect against, but it is weak or no combustion in one of the twp tested cylinders. Maybe lean due to a (partially?) blocked injector, might be a single plug wire or plug. For some reason a tested cylinder has slightly colder exhaust, and the protection relay turns off fuel to all four cylinders served by that ignition system. Of course, once the protection relay drop fuel flow, the exhaust for sure will get even colder for all served cylinders.

Should you bypass the system? In my opinion, you should not except for diagnostic purposes. Add a jumper, find the weak cylinder with cooler exhaust that's triggering the protection relay, fix the problem, restore the protection. Borland's "solution" looks way to permanent and comfortable. I'd rather see a set of jumpers passing through a softball or a big orange tape streamer, something big enough that you can't help but notice it's there as you drive for the testing.

Just by the factory bypass relay, it's cheap.

what is the problem that was being corrected? what does this have to do with cats? and what is the factory bypass relay?

Here is my understanding of the system: The factory IMS (Ignition Monitoring System) was designed to measure EGT's and protect the cats from overheating/catching fire. The idea was that if EGT's dropped below a specified level then the ignition system must not be working correctly and raw fuel would be dumped into the cats. The ICM is part of the IMS system and it would shut down the fuel to either the left or right bank depending on which side the EGT was deemed too low. This resulted in a rough-running/limp mode type of operation designed to get you off the road...but not designed to drive any distances as damage could be done to the engine and drivetrain. The IMS system components are prone to failure. The original poster bypassed the ICM to eliminate the fuel being shut down. Porsche makes a bypass relay for this system for use on cars equipped from the factory without cats.

thanks for the explanation.

where is this relay located? is this as simple as installing this bypass relay and leave the modules in place? currently I have cats, but plan on X pipe and delete soon. is this a procedure that I will want to do? not sure I understand the benefits? any issue with doing this prior to cat delete?

Paul, all of this has been covered in the past. With a couple of the keywords from gbarron's response, you should easily be able to find the relevant materials on the function of the IMS system and discussions RE: the reasons for bypassing it if necessary. That said, you necrobumped this thread from your thread on voltage drop. I'll submit that nothing in the IMS system could possibly have anything to do with your voltage drop issues. If you have problems with IMS malfunction, you'll know, because you'll be down about 150 hp. This isn't the droid you're looking for.

That's because this thread is from 2009 and the images were hosting on image shack instead of Rennlist and something has happened on their end.