[Boghog]

Failure mode effects management (FMEM) is an alternate system strategy in the powertrain control module (PCM) designed to maintain vehicle operation if one or more sensor inputs fail. When a sensor input is perceived to be out-of-limits by the PCM, an alternative strategy is initiated. The PCM substitutes a fixed value and continues to monitor the incorrect sensor input. If the suspect sensor operates within limits, the PCM returns to the normal engine running strategy.

 

[bootjack]

so how do you find out which sensor is bad?

 

[Skyhawk]

The above strategy is often referred to as the "limp in mode". The engine runs on a rich mixture because the "computer" is not getting the information it is programmed to look for. A lean mixture can do a lot of damage to the engine so the "mixture" is rich as a precaution. The rich mixture can ruin the catalitic converters if not corrected. A scanner, as well as "on board diagnostics", can identify the sensor that is out of the expected perameters, but that does not mean that the sensor is bad. The sensor may have a bad connection, a broken wire, or grounded wire. A sensor may also be reporting correct information, e.g. an O2 sensor reeporting a contiuous rich condition say due to a bad injector, or a lean condition due to a vacuum leak. The "CODE" is a guide to finding the problem, but does not automatically pinpoint the problem. Do the diagnostics.

 

[bootjack]

thanks....I'm trying the diagnostics...but the KOER test did not go as the Haynes book or other sources have indicated....it went straight to flashing codes......codes retrieved under the KOER test were => 998 then 224.

 

[bootjack]

so my question is this....when there is a hard fault present in a OBD 1 version (such as my 92 Ranger) to give a 998 code under the KOER test, does the system just bypass all the other flashes or codes that the instructions say, such as the eng ID, etc. and goes straight to the 998 code ? Because if it does, then that caveat needs to be put in the written instructions as to what to expect.

 

[Skyhawk]

You are talking about The EEC IV system and I'll have to get out the "Rozetta Stone" tablets from way back then. The 998r code is Hard Fault Present (Failure Mode Effects Management mode). I'm looking for an explanation for that code and the perameters of what itu means/does. Hang on while I read some ancient history.

 

[Skyhawk]

Note: The 224 code indicates an erradic signal from the IDM (Ignition Diagnostic Monitor) to the processor. Try checking the ignition (coils and IDM) connections for corrosion, loose pins, grounding, etc.

 

[bootjack]

I checked the output of the coils today and found that the front coil (2.3L with dual plug DIS) was not firing plug 2 & 3, intake side. Plugs 1 & 4 from same coil are firing, so 12volt to coil is there. Then checked for signal from ICM to fire coil...not there for that coil,... but OK for other coil in same unit. Then checked rear coil pack....signal present on both wires to primary connector.

Next I checked continuity from connector at coil to ICM connector...OK. Must be the ICM not producing signal (GRD) to fire coil?

BTW-I did some further research and found that in the older EEC-IV units it seems the KOER test does default straight to producing a 998 code when there is a "hard fault present"....

 

[bootjack]

Pulled the ICM and had it tested at Auto Zone....first test it failed then the next 5 tests it passed. Reinstalled and problem was gone ..... it was just a tease .... the problem came back after I put in new plugs and wires. New ICM installed and now have fire on plugs 2&3 on intake side. So in essence...the electronic points were not closing.....

BTW-found an error in my copy of the Haynes manual. Wiring diagram for the ignition system shows pin 9 of ICM connected to pin 1 on "secondary" coil pack....not on my truck...Pin 9 from ICM goes to pin 3 of coil pack to fire plugs 2&3. Pin 1 on coil is primary connection for plugs 1&4 and is connected pin 8 on ICM.

Also found a good resource for part info and troubleshooting....... wellsve.com.