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Corey872

Swapping Just the ECU?

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I gave my 04 F150 it's first dose of E85 yesterday.  Everything seems to be doing fine, except, of course, the CEL came on within a few minutes of running.

 

Then I started thinking - these trucks were available with the FFV option.  I wonder if I could just swap out my ECU for a FFV ECU.  I know a lot of the vehicles that get converted don't have the FFV option.  Just curious if anyone has ever swapped just the ECU from and identical FFV?  Thoughts on chances for success or reasons for failure?

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Sounds like a good idea, but I think you'd have to see if there are any extra sensors on the FFV that the normal truck doesn't have.  Also, see if the wiring harness is different.  Something else you might think about is flashing the ECU with the FFV program, although I highly doubt that it'd be that simple.

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I've never heard of anyone actually swapping out ECU's but a reflash is certainly a possibilty ..  Seems Hotrod Larry or GT reflashed one of thier trucks ? 

 

 

Corey how many gallons of E85 did you add ?  I keep seeing more and more non flex able to run up to 60% ethanol without any conversions ..

 

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Sounds like a trip to the junk yard is in order to see if the ECU has the same design plugs and such, then a visual exam to see if there are any spare hoses, sensors on the FFV model.

You might also dig up a wiring manual for both vehicles and see if they wiring harness is the same.

 

On some cars they use the same wiring harness on several different models and just leave a couple wires unconnected. My subaru has a power plug for a rear window washer that is not available in the U.S. model for example.

 

Larry

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I think I put about 25gal of E85 in the 27gal tank - but I think my last fill was with E10, so what does that work out to??  2*.1 + 25*.85 = 21.45 gal ethanol in 27 gal gas = E79.4

 

The truck runs OK, but just threw the CEL.  On the other non FFV's that me and my friends have put E85 in - IIRC when we retrieved the code, it's usually something to do with the fuel trim out of range.  Basically it seems like the ECU is able to control the ethanol fine, but it seems like there is some computer code limit that says " if fuel trim exceeds 25%, set an error code"  The E85 usually pushes it around 30%.  Running E60 would probably keep the trim below this software coded error limit and not set the CEL.

 

As far as extra sensors, I'd have to check into that.  The last I knew, most mfr's were simply using the O2 sensor feedback to make adjustments and estimate the % of alky in the tank.  I suspect they may use that to also bump the timing a little or otherwise optimize the parameters a little more for E85.

 

After all, the FFV is a free option - this is from dealers that charge $300 for a $5 can of undercoating or a  can of Scotch-guard, so there can't be much difference.

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it seems like there is some computer code limit that says " if fuel trim exceeds 25%, set an error code"

 

Right most OBDII ECU's in non-FFV's seem to set a max fuel trim of 25% as an error condition, assuming something is broke (like an intake air leak). The fuel trim system works just fine off the O2 sensor within its adjustment range. I use that to my advantage on my system. I have over sized injectors and an adjustable fuel pressure regulator. I reflashed the ECU to have zero fuel trims on a blend of 50% E85 and 55 psi fuel pressure. I run the base fuel pressure up to 65% when I am running 100% E85 and dial it down to 45 psi when on gasoline and the ECU adjustment is enough to handle both extremes as with the fuel pressure changes the fuel trims are only +/- 15% with that setup.

 

Larry

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