If i'm getting good voltage to my ficm, but still getting poor fuel economy could the ficm still be bad. By poor i mean 9.5 city and 13 highway. by the way its a 05 fx3 with 110,000. i've only had the truck 5 months so i'm workin out the bugs.

 

Is the truck lifted, or over size tires, when was it last serviced (fuel filters, air filter etc).
Many things can contribute to mileage, driving style, gearing, mods (not all mods make mileage go up).

Have you checked the FICM performance IE: main Power Voltage, Logic Power, etc? I use a scangauge II and monitor those and many other items using the X-Gauge features. There are many devices that can and will do this, we all have different preferences in interface and features, but this works for me.

-Mark

 

i have a scan guage and all my readings are ok, the only mods i have done are blue spring, and no cat or muffler straight piped. everything else is stock tires, gears, lift.

 

I certainly don't profess to have the answers, but I will say this, the best I'm getting around town is maybe 10-11 and out on the interstate a best of 15-16. That's measured by topping off the tank running the miles a topping off again, then the manual computation. I'm kind of a leadfoot and tend to push it to get the truck rolling as it is a lot of weight.

 

OK, my thoughts on this subject.

My FICM would start the mornings low, like at 39-40v. Then it would rise to 48v and then I would start the truck. It only takes 10 seconds for the FICM to do this. Once warm, it would stay above 46.5v. All the other readings for the FICM were right where they needed to be.

As this has progressed, my fuel mileage stunk. I haven't been above 14 mpg, with almost all highway driving. One weekend we even took a trip and only got 13.7 mpg there and back. Hand calculated. My "lie-o-meter" hasn't seen very much above 14 mpg.

Fast forward to this week. I decided it was time to send the FICM to Ed and have it repaired. While it was out, I pulled the turbo for a cleaning. Well, that didn't go well!!! I broke a post off where the vanes ride. So, much for that turbo.

But, happy days! Bought a Powermax GT3788VA turbo. I just finished fixing the leak I thought I wouldn't have. Took Her for a ride.

I drove 44 miles, my "lie-o-meter" when I returned says 17.5 mpg. Now, this is not hand calculated, but, it hasn't read that high in months! Can't wait for our little trip this week to see where it actually stands.

So, what did this increase in mileage? FICM fixed and up graded with the Atlas 40 tune? Or, the Powermax Turbo? Probably both.

But, I'm guessing the the up graded FICM had the most to do with it.

That is my opinion, for what it's worth!