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Old 04-07-2013, 04:51 PM
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MPG's dropping, suspect batteries or ficm

I've been noticing my mileage dropping for the past few weeks, gradually. About two months ago I'd fill up, and my calculations would average 18mpg. Now I'm down to about 15. Not the end of the world but definitely noticeable.

I've also noticed when I first start the truck in the morning, my alarm goes off on my CTS letting me know the FICM voltage is low, but it only last seconds. Within about 5-8 seconds from cranking, the FICM voltage is at 48v. However, the dash lights and the screen on the CTS flicker a bit until I get down the road. This is why I suspect I may be having an issue with the batteries.

Driving down the road with the truck fully warmed up, the FICM voltage fluctuates from 47-48v at 60-65mph. At 70-75mph, it holds at around 45v.

Other than that, no other issues.

My plan was to take the truck in and have the batteries tested to see if they're the culprit. They're very new looking Motorcraft batteries but do not have a production date on them.

Is there anything else I may be overlooking?
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Old 04-07-2013, 06:48 PM
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Get the batteries checked asap. Bad batteries can kill an FICM. FMP should never drop below 47volts.
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Old 04-08-2013, 03:22 PM
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had simular prb ficm was corrupted led to injector failures on my 03 check batteries asap
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Old 04-09-2013, 06:26 PM
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Got an appointment with the dealer friday to have them checked. Thinking about just fogetting them and throwing in a new set of Interstate batteries. But if these are under warranty, free is better than nothing.
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Old 04-10-2013, 02:00 PM
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Batteries tested good. Did a load test and a test of the water, no dead cells and good cca's. I read some other threads on here stating the ficm shouldn't drop below 45 volts, but a few say 47. Which is it?
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Old 04-10-2013, 02:18 PM
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Ficmrepair.com states: "Again, if the voltage drops below 45, even for a second, during any of these tests, the FICM needs repair." So I guess 45 is the magic number.
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Old 04-10-2013, 08:15 PM
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Interesting... so maybe it's an intermittent problem, but I'll monitor it for now. On the plus side, I filled up last night and averaged 18.22mpg. The last tank had been purchased at a larger Mobile station rather than the local, small Chevron outlet where I normally fill up.
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Old 04-11-2013, 05:41 AM
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You'll find that different suppliers have different diesel quality, and diesel in summer time and winter time are different also.
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