89FrontPorsche

Hey all.

Car has been sitting for over a year while I was otherwise engaged in many other projects, my job and so on. I parked it when the steering rack went bad and have now replaced that and it works great. Learned lots of new cuss words doing it...but escaped with all the skin on my knuckles still intact.

However, upon start up car did the usual burp and buck routine until the computer got it figured out but...after just about one minute or less, it bumps to four cylinders, acts like the entire battery has come disconnected/reconnected and gives me a message code 4 on the inst panel.

The car has a new computer board from 928 Intl.

It starts and runs fine, idles fine then after about one minute, goes into four-cylinder mode. I suspect it's a bad relay on the ever-ugly electric board as I recall reading about that some time ago (years) but wonder if anyone else has had this symptom. I'm betting it's a simple fix and I'm not real keen on diagnosing a bunch of extraneous junk to find out it was just a relay.

I've heard it referred to as "limp home mode" but I really can't tolerate driving the car like this...and haven't....and won't. Might be dirty/oxidized blades on the relay(s)?

However, I'm open to suggestions.

Thanks in advance.

Wisconsin Joe

Well, "limp home" mode is generally used in reference to the MAF, which will go into a default fuel map if it malfunctions. It's enough to keep the car running to get you home, but the car runs like crap.

What you are describing sounds more like the Ignition Monitoring System - It's a temp monitoring system that is intended to detect a lack of spark, by "noticing" lower temps in the exhaust. This has led to raw fuel being dumped into the exhaust, reaching the cats and starting a fire under the car. It's not so much a "limp home" mode as a "shut the fuel off to half the motor so the cats don't start on fire and burn the car to the ground." The uneven and rough running from half the cylinders not running is not good for the car, and has snapped torque tubes before.

If it is the IMS, there should be a LED illuminated on the EZK box.

More info in this thread:

https://rennlist.com/forums/928-foru...ng-on-4-a.html

worf928

Sounds like IMS: Follow the link from WJ. Then continue from there with additional searches for research as needed.

If the IMS is triggering it's doing you a favor 90% of the time. You can bypass the IMS relay to help you find the issue. But, don't just stop there; figure out what the issue is.

GregBBRD

Remove and check both coil wires....at both ends of the wire. Get a mirror and look inside the coil and the distributor cap, looking for "green".

Mrmerlin

and to carry on what Greg suggested,

before you touch anything,

remove the intake tubes,

then run the engine in the dark,
looking at the coil wires for sparks jumping,

NOTE the coil wires should not touch any part of its run.

If you do find a coil wire with jumping sparks you can buy new coil wires.

dr bob

The IMS relay is intended to protect the car from dumping fuel through cylinders that have had ignition failure. It has a couple thermocouples in the exhaust, one on each side, and shuts down fuel to a bank of cylinders when it detects significantly colder exhaust from that bank. The 'banks' are divided two cylinders to each side of the engine, matching the cylinders connected to the two independent ignition systems. A simple Dexter Test has you start the engine from cold, run for maybe 30 secs and shut it off, then immediately use your right hand to test for even temperatures at each exhaust tube. If you have one ignition system failed, you'll easily find four pipes that are colder than the others.

The system responds to failure of either of the two cylinders under whch the probes are placed. There was a TSB and a manufacturing change that moved the probes in later cars. Regardless, if you find fewer than four cold exhaust pipes with the Dexter Test, that could also guide you to a problem. It just isn't a total failure of one of the two ignition systems.

If you find fewer than four pipes colder, you get to diagnose whether the cause is ignition failure on the cold cylinder, or perhaps a sticking or varnished fuel injector there. From your description, there was no storage prep done, so the fuel was not treated for storage. So don't limit your diagnostics to just ignition, as the IMS will 'protect' a bank of cylinders regardless of the cause of no-fire in a cylinder with a probe underneath.

DIY Owners should have a decent IR thermometer in their tool collection by now. One of those would be an OK substitute for the right hand in the Dexter Test. Regardless of the actual temperature detection method, limit the amount of time spent running on fewer than 8 cylinders, and test immedialtely on shutdown of the engine so there's less time for heat to migrate to the cold exhaust tubes from the hot.

PHIL928

The IMS relay can be jumpered with 3 spades connected together. It's the easiest option to check this first before pulling tubes, and coil wires.

I will try and find a picture of orientation.