MPG Drop For No Apparent Reason - Diesel Forum

tperk100 · 11-12-2012, 10:49 PM

I bought my truck new in 04. I have an SCT SF3 Programmer and use the least aggressive program. For 8 yrs I have enjoyed about 20 MPG at 55-60 MPH on the highway with no towing or hauling load.

All of the sudden my mileage has dropped to 15 MPG at ONLY 55 MPG. The truck starts, accelerates, and otherwise seems to run just fine. There is no hesitation, smoking, etc. Boost readings seem OK, and there are no error codes present. Have not made any changes to vehicle in years.

I actually calculate MPG vs relying on computer.

Any thoughts, suggestions etc on what might be causing this?

Thanks much.

Mustanglee · 01-06-2013, 05:53 PM

Have you had it into the Ford Dealer recently? Did they reflash your computer? I had a similar situation with my '05. Mileage dropped 20% after Ford did the "upgrade".

tperk100 · 01-06-2013, 06:41 PM

Have not been to dealer...

However, I have noticed that it just started running extremely rough at startup in 30 degree weather...smooths out in about 1 to 2 minutes. Wonder if this could be related to MPG problem.

Ty1 · 01-06-2013, 07:08 PM

If it is starting to run rough, that's a good sign that your ficm is starting to go bad. When it starts getting weak and doesn't give the injectors enough power, it'll cost mileage. When it has bad mileage, it then proceeds to running rough. My 04 went from 21 mpg to 12. No more than a month later it started running slightly rough right at start up. Now it is a b!tch to start. My FICM voltage is 37 volts when running. Should be no less than 46. Getting it rebuilt. We'll see what happens in a few days.

tperk100 · 01-06-2013, 09:03 PM

Ty....Good info,. I will look into this. Thanks

Ty1 · 01-06-2013, 10:43 PM

No Problemo. Repost on what you find out!

HeavyAssault · 01-07-2013, 06:08 PM

Another VA driver!! FYI another forum is having a GTG soon if you are interested. Hope the FICM is your only issue. Pretty simple to fix.

tperk100 · 01-07-2013, 10:19 PM

So far I have disconnected, charged, and load tested my batteries to find out that they are both in excellent shape. Interestingly I had to charge the batteries for about 3 hours each on the 25 amp setting to bring them to full charge according to my "smart" charger. At this point they both measured 12.6 volts under no load with a DVM.

I have also programmed my ScanGuage II to show 3 different FICM related voltages, including the main power of 47 to 49.5 volts . Tomorrow I will be monitoring those voltages as I start it up, as well as the charging volts when things have settled down. If charging volts (13.3 or so) are low, I will be installing a replacement higher amperage alternator.

This is a little premature, but I am already of the opinion that I might simply have clogged up fuel injectors. I have ordered the Hot Shot Diesel Duo....which I should probably use at 90,000 miles anyway. If my test tomorrow show any suspicious FICM voltages, I am going to order a tuned FICM from.......... FICM Repair.com - Your Source for FICM Repair

bismic · 01-08-2013, 06:58 AM

Make sure a brake caliper isn't hanging up or the A/C compressor clutch isn't frozen (inspect the belt for wear or shiny spots on pulleys). Low tire pressure is a killer also

tperk100 · 01-08-2013, 09:21 AM

Mark,

Thanks for your reply. Front tires are always 60 and rear are 80. Check them regularly.

If caliper was hanging up, wouldn't I smell it? If not, how would you recommend that I check for this?

A/C and Defrost work properly so doesn't that say the clutch is working correctly?

Thanks again.

tperk100 · 01-08-2013, 01:21 PM

Update - Upon starting today, the FICM main voltage started out at 47v, but after running for just a minute or so, it dropped and stayed at 27-31 volts. Alternator output voltage was 13.2 with some accessories running.

I have ordered tuned FICM and 100 amp alternator and wiring kit from FICMRepair.com, and the DUO additive package from LubricationSpecialists.com.

Will post results when all is installed.

Ty1 · 01-09-2013, 07:24 PM

I think we found your problem. It should hold that 47 ever after running for awhile.

ryhed · 01-09-2013, 07:42 PM

It probably wouldn't hurt to run cleaner in the tank a few times to clean up the fuel side of the injectors and run your oil additive to clean up the oil side of the injectors, clear up any stiction issues. AR9100 seems to be the new product to use for stiction.

Also we are on winter blend diesel now so expect drops in mpg.

AR9100 vs rex-x

Band_Member · 01-10-2013, 07:31 AM

Quote:

Originally Posted by bismic

Make sure a brake caliper isn't hanging up

Exactly what I was thinking.

To the OP, best way to check that I've found is to get an I/R thermometer and check your rotor temps when you stop for fuel on a highway run. Just last weekend I found my left rear sticking and the temp was well over 400°.

The caliper itself was not sticking it was the pads in the slots on the caliper bracket that froze. Corrosion is a big issue in my area due to close proximity to salt water (nor do I drive on the beach).

Since this has been an ongoing issue in my case I make it a point to make the rounds and check the temps of my rotors while the truck is being refueled.

tperk100 · 01-10-2013, 08:08 AM

Thanks Band,

I live by Salt water also. Just happen to have a couple of IR Thermometers, so I will do exactly what you suggested. However, I still think the problem is the FICM. Will post results later.