Excuse us Willard, the poster is asking for owners of a 2009 FEH to reply.

 

I had something very similar in my 2009 FEH today. Outside air temp was 97 on the way home. I was running Auto A/C with the temp set at 75, on the interstate at around 60mph and noticed the RPM was up to around 2400. This was with very light pressure on the accelerator. I turned of the A/C and RPM dropped to around 1500.

I turned the A/C back on and it shot back up to 2400. I then coasted for a short time and the RPM went down to around 1100 and the SG II showed Open Loop/Instant MPG=9999 (2009 has fuel-cut when coasting). Any pressure on the accelerator and the RPM immediately shot up to around 2400, almost like an on/of switch. No matter how lightly I accelerated I could not get the RPM any lower without completely taking my foot off.

What was interesting is the instant MPG on the SGII would vary with the amount of pressure on the accelerator. Very light and I could get 40+ instant MPG, with RPM at 2400. Accelerating harder would get it down to the low 20's and upper teens.

I've noticed this a couple of times with temps in the 90's but this is the first time I played around with it (just shut off the AC before). Temps have only recently been in the 90's.

I never noticed this in our old 2007 FEH.
-- Rick

 

There is an engine performance issue at higher temps (or altitudes, humidity plays a role too since water vapor displaces oxygen). I wouldn't have thought it would be objectionable though.

The engine controller monitors air density: temp & pressure. From these it determines fuel to be injected for the commanded power level. Since the FEH is partly electric and the generators are fixed excitation (Permanent magnets) the way it increases power in the electric side is by increasing rpm.

So, as the air gets hotter, less mass of air is available for ingestion, the controller injects less fuel and less power is produced at a given rpm. Then the controller ups the rpm to produce the same power.

But I wouldn't have thought this effect would be objectionable in performance.

For those who have pilots licenses I'm speaking of density altitude here.

 

Being a former AF controller, I understand density alititude & etc. But it appears in this case that the FEH is programmed to begin the behavior at around 95-97 degrees. I would think that if it were simply the environmental conditions, then the change would be more gradual; the RPM would go higher with temperature. Instead, there seems to be a cutoff temperature, above which the engine will run extra RPM if the A/C is operating.

As to objectionable in performance, no, not really. But the key to good MPG is lower RPM, and adding (in the 2008 FEH) 600 RPM means lower gas mileage. THAT is the issue, not performance.

 

Right about the more gradual thing... That's why I spoke of being surprised at it being objectionable.

But the density altitude thing is only half the pic. This also involves an electrical power path. Some energy goes to the generator and then to the traction motor when cruising. Recall that the engine is not hard connected to the wheels, the ring gear of the planetary gear set is, along with the traction motor.

The next element is that the generator and traction motor (electrically the same kind of machine) have permanent magnet rotors. The only way this generator can increase power output is to increase rpm. The only way to increase its rpm is to increase the ICE rpm.

And my point is that the combination of the two seems to be problematic. Not trying to say there's nothing wrong, take it to the dealer if needed. I wouldn't like the symptoms you describe either.

Adding rpm increases fuel consumption, yeah, I got that. When cruising on the interstate I typically use the speed control, but bump it down and up when hill climbing. I have found that keeping rpm less that ~4000 make a real difference!

 

I seem to recall that people have spoken to the dealer on this issue, but don't quote me on that. But apparently it is just the way the FEH has been programmed. I have now seen reports on Pre 2008, 2008, and 2009 models, although it appears that the 2009 may have different parameters.

Speaking of fun times, did you ever use an AMPI? You wouldn't unless you were prior AF in either the Navigator or Air Weapons Controller fields...

 

In all of the posts, I have not found any reason to suspect anything is "wrong". Conditions are just outside of the normal and customary envelope people are used to in mild weather.

If you think it behaves strangely at above 95 degrees...
Wait to you try driving it below zero degrees!

At -15 my 2005 runs at 2400 RPM at stoplights with my foot on the brake!

 

Based on Rick's comments it appears that this behavior is probably normal for 2008-09 FEHs. Perhaps one of Ford's better ideas...

I have never seen this in my 2005 even with 118F outside temps with 120F battery temp. Apparently Rick never saw it in his 2007 either.

 

Desert Dog:
You don't understand how synchronous machines work, sorry. Don't be so ready to tell someone he's wrong.

In a synchronous machine (as both the traction motor & generator are, they're electrically equivalent but differently sized) there are two ways to increase power: rotation rate (eg rpm) and excitation to the rotor (eg magnetic field strength). Since these are synchronous machines with permanent magnet rotors the excitation is necessarily constant.

My statement about increasing rpm assumed that the road speed was being held constant by the controller. Your citing of the equation is incorrectly used.

I happen to think this is normal if unusual operation. If I see this in mine I'll just note it.

 

Steve,

My 09 has been doing the same thing lately (92-95 degree days here lately).
This NEVER happened with our 08.

Yesterday, when my 09 was cruising at 40-45, the rpm was about 2000 and the ac was on. Because I had read this post, I shut the a/c off without moving the gas pedal at all and the RPMS dropped to about 1300, after about 6 seconds, I turned the A/C back on and oddly enough, the rpms stayed low even with the compressor cycling..

I'm not sure the higher rpms are detrimental tho, because I am not seeing a drop in mpg.