I have a 2001 mustang GT, and it has been getting electrical gremlins lately. The headlight began with light flickering, and have gotten much worse lately. When I run the heating/cooling system fan, the fan motor will change speeds up and down. Just a couple of days ago, the battery light on the dash began flickering and the car now sputters through the exaust. I believe the problems all point the the gem module, as nothing else makes sense? The gem module is like $520.00 retail from Ford, and I don't want to waste my money if it is not in fact the problem. Has anyone on here ever had the same symptoms as me, or are there any Ford techs on the forum who may be able to help me out?

Thanks.......

 

The GEM controls none of those things...

From the shop manual:

Check the connections and fuses/breakers in the battery junction box (the "fuse box" under the hood), and also suspect the ignition switch as it is the master control for the sub-systems you mention.

It could also be the battery, an intermittently shorted cell could cause the problem you list--get a high current draw-down test performed and see what the voltage looks like after 15 seconds at 250A-300A draw...

 

Thanks for the input on my post, I appreciate it. I do not seem to have any extra draw on the battery, but after two days of sitting there is not enough in it to start the car?! I have a sniper tuning program in my ECM right now, and wondered if the battery going dead on me all the time erase any of the non-factory programing?! The car burns a ton of fuel (9mpg.), the air/fuel could possibly have been screwed up with constant battery draining?! The alternator is charging the battery when I am cruising, but lately the battery light has been flickering driving along?! I have eight weeks to get my car straight and re-tuned for Tasce Ford day at New England Dragway, so I need to get this problem resolved as quick as I can. I called ford to ask about a BCM, and they told me that my vehicle does not have one, are there any other replaceable modules that may point to any of my symptoms?! Thanks again for your help, I am just doing a little head scratching with this issue.

 

I'd say its almost possible to be a bad diode in the alternator. It'll cause a couple of similar symptoms. If you kno anyone else with a mustang see if you can swap alts for a few hours to see if it alleviates the problem

 

The battery's going dead will not affect the tune, it's stored in non-volatile EEPROM, however it will cause the KAM (Keep Alive Memory) to clear which will mean the will have to relearn the adaptive fueling settings (long term fuel trim, idle air trim, etc.).

To go by the book the engine should idle for 15 minutes after clearing the KAM so that the idle air trim values can be relearned. The LTFT values are learned over time and are used during open-loop operation, though they should not affect AFR as greatly as you report.

Also, the battery should not be going dead in 2 days--it should be able to sit 2 or 3 months before it would not start the car. You need to get a high-current draw test run on the battery, or just get a new one if it's old. You can get a nice 100A tester at Harbor Freight for $15 or (it's almost always on sale); or get a very nice 500A tester for $60 (also almost always on sale).

These cars are quite sensitive to battery condition, though again I doubt that is causing the overly rich mixture.

How old are the front O2 sensors, are they wired correctly? What size injectors/MAF are you running?

Also, if you like, send me your current tune's .pcm and .txt files, and your OEM tune's .pcm file--I will take a look at them with DeltaForce and see what I can see (cliffyk@paladinmicro.com)...