Weird MPG issue - Ford Powerstroke Diesel Forum
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Old 06-28-2013, 02:11 PM
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Weird MPG issue

Not sure if this belongs here or in the Engine trouble section, but this section gets more traffic. I didn't notice this issue until we started getting our hot dry Summer days, I sort of expected that my MPG was "normal" but now that we've had a few days in the 80's, I have started noticing a trend. Now these numbers come from the Lie-O-Meter (LOM), which has been within 4% (max) of hand calculated numbers. Filling up at the observed intervals would be crazy.

Start off by saying the truck runs great, no misses or weird sounds, which is why I thought the MPG was normal.

FWIW, my test track is 25 miles of some of the flattest interstate you will ever drive on. I think there is 45 ft of TOTAL elevation change from point A to B and NO corners. There is one section that slows down to 55MPH for about 5 miles then back up to interstate speeds.

Poor MPG when outside ambient temperature is below 70f (any speed)

Lower MPG than a lot of guys post on here, I am getting 13.0MPG city 14.5-15MPG highway. I have on a couple occasions made a conscious effort to stay at or below 70MPH without appreciable gains in MPG.

This afternoon for example. Outside temps are right around 75f. My truck had been sitting in the direct sunlight (black, it gets HOT). I jump in it to take off into town for lunch with an old coworker. Starting the LOM reads 14.1MPG. The first 2 miles of the trip are 55MPH or less, then turn onto the interstate and its 75MPH, about 3 miles of 75MPH before it drops back to 55MPH for the remaining 4.5miles. AC was not used. When I pull into the restaurant to park, the LOM has climbed up to 14.4MPG. (good trip, the LOM never dropped in MPG)

I eat lunch, then take off, I have to make 2 stops before returning to work. One at a bank ATM to get out some money, and a second to pay that money to somebody. By the time I am pulling out of the last parking lot, the LOM MPG has dropped to 13.7MPG. I am also using the AC at this time so I can make a couple phone calls without traffic in the background. LOM MPG drops to 13.6 as a low and ever so slowly creeps back up to 14.0 as I am getting off the interstate to park at work. As I idle into my parking spot it is back to 14.1MPG. (not great, but not awful return trip)

If it is hot outside and I have to do in town commuting I can keep the LOM up between 15.0-15.5MPG. If it is cold outside it will drop dramatically, sometimes recovering, sometimes not.

Another example
A few weeks ago I had to drive 65 miles each way to a small airport that's out in the boonies. Posted speed is 55MPH (so you know I drove 60MPH).

First leg of the trip:
3:30am CST outside temps right around 60f. I take off, as soon as I get off my gravel road, and then off the short section of state highway. I set the cruise at (you guessed it) 60MPH. There's nobody around so hardly any speed fluctuation at all, half of the roadway was so flat you can see Canada, the other half was low lying rolling hills. When I got to the airport, the LOM was reading 17.3MPG. (side note, the previous day I had made a 80 mile trip @ 67MPH with 76f temps, no wind and the LOM also said 17.3MPG upon parking it)

On the way back around 8:30pm CST, temps had climbed up to nearly 78f and it was hot and humid, I'm a chunky fella, I don't like temps over about 71f I get all sweaty. But I digress. I took off from the airport, made a short stop in town for some fast food (Taco Johns) and then hit the highway. LOM MPG drops to 17.1 between start up and the time I get to the highway, but that recovers to 17.3 within 10 miles of town (again, cruise control set at 60MPH). On this return trip I make one short detour to check out the lake levels where we launch our pontoon, about 20 miles into the trip, I turn onto a 40mph blacktop road and I follow it for the next 4-5 miles, at the posted speed limit or below, I don't like windy backroads that have water/swamp/sloughs on them. But as I'm watching the LOM I expect it to start dropping, but instead it starts raising?

By the time I get to the boat launch the LOM MPG has climbed up to 17.5MPG, but then I let it sit an idle in the parking lot while I snap some pictures. It drops back to 17.3 by the time I leave.

I follow another windy back road (blacktop paved) until I get back to the county road and head home. The entire trip home the LOM MPG meter kept climbing until when I finally parked. At that time it was reading 18MPG.

The next morning I get up and head to work (65f 25 miles @ average speed of 70MPH) and the entire time the LOM drops and by the time I get to work it has dropped to 17MPG. The remainder of that week I tried to keep speeds under 70MPH and it continued to drop and by the end of the week when I filled it I had a LOM reading of 15.5 and a hand calculated 15.25MPG.

My guess:
It really seems like one of the switches/sensors or wiring harness is susceptible to temperature changes. When the outside temps are hot or when the air speed is slow and the engine heat is allowed to heat soak the offending part, closing up the tolerances and then the truck runs more efficiently. I'd compare it to the difference in running a gas motor in Open loop vs Closed loop.

I monitor the essentials using the Android Torque app
GPS Speed (Meters/second) -- (note, this shows miles/hour)
Battery Voltage(V)
Coolant temperature(From TCM)(°F)
Engine Load(%)
Engine RPM(rpm)
Exhaust Back Pressure(-)
FICM Main Power(Volts)
GPS Altitude(ft)
Injection Control Pressure(psi)
Intake Manifold Pressure(psi)
Speed (OBD)(mph)
Turbo Boost & Vacuum Gauge(psi)
VGT Duty Cycle(%)
Engine Oil Temp(°F)
Injector Pressure Regulator Duty Cycle(%)
Turbo Boost (psi)

Currently there is no Malfunction Indicator Light (MIL)

However over Fathers Day Weekend, I did a 120 mile tow each way in 80f weather pulling my pontoon (same north Dakota flatlands) at 60MPH with AC on into a 20-25mph sustained head wind on the way out and it did record the following errors, I cleared them and they have not returned. FWIW, I had some 228-229f EOTs during this drive. MPG was low as expected 7.6MPG hand calculated. This never engaged a MIL.
P0341: Camshaft Position Sensor "A" Circuit Range/Performance (Bank 1 or Single Sensor)
P0528: null
P0611: null
P0645: A/C Clutch Relay Control Circuit (I had been doing work on the AC the day before and this is probably residual from that work)
P1378: null
B1352: nul

I cleared these codes using Torque and made the return 120 mile trip @70mph with the AC on and the same 20-25mph tail wind now and got 12MPG, no overheating issues or re-occurrence of the codes. I typically treat codes the following way.

One time occurrence = random, no impact.
Second occurrence = start planning on replacement (but clear it again)
Third occurrence = repair should be scheduled

If my results were more consistent I'd probably write it off as "that's the way the ball bounces" and learn to live with it. Everything looks like it is within spec but something feels wrong. If anybody wants to rack their brains against this one, I have the Torque App logs from any/all of the previously mentioned trips.
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Old 06-28-2013, 06:01 PM
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just an idea but oil your using thicker than normal? 15w-40? thicker the colder it gets hence more work needed to do the same task.

also mabe someone will chim in with more info but if the cam sensor is going bad won't it cause retarding or advancing onthe injector timing due to ficm getting false reading?
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Old 06-29-2013, 06:37 AM
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I have only had this pickup for about 2 months. The previous owner or the dealership that took it to auction changed the oil right before I purchased it, according to the sticker I found under the floormat it is due for a change during the first or second week of July. I don't know what brand is in there now, but when I change it I had planned on going to Rotella T5 5-30W. Maybe I will move that you a week (which means I need to get off my keister and buy/order a motocraft/raccor oil filter).

I am a bit worried about that cam sensor,the replacement therapy instructions/posts that I read say that it is a delicate part and has been known to break upon removal.

I am also wondering why it didn't set a check engine light.
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Old 07-15-2013, 08:41 AM
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Over the weekend, I changed the oil to Rotella T6 5-30w, used a Ford filter. I also changed the fuel filters, the PO had put in non-Motocraft filters, I replaced them with genuine Motocraft parts.

No change.

There are a couple issues that I'm going to be checking out shortly.

1. I was informed by a Ford Tech (off the books) that since my truck is a 2005 it *may* not kick off an Check Engine Light (CEL) if I drive with the EGR unplugged (he unofficially told me to do an EGR delete -- I guess technically he'd be my step-brother-in-law -- I've never met the guy, seems solid)
2. IAT-IAT2 delta issue, somewhere I read that the original HEUI programming was designed to start cutting power when the IAT/IAT2 delta was greater than 40f. From logging, mine is usually in the 60-80f range. Trouble is that I can't remember which document that was read in. So my plan is to remove and scrub the Compressed Air Charge (CAC) tubes and the intercooler, I suspect that everything is coated with oil as was evident by the amount of oil I saw in the cold side CAC when I upgraded from the original plastic to a 2004 aluminum CAC.
3. I am going to recheck/reclean the IAT2 sensor and EGR to make sure they are not oil fouled.
4. I'm also monitoring the Engine Coolant Temperature (ECT) as it seems that my ECT is dropping below 190 way too often. The thermostat was replaced by one from Napa (lifetime warranty) I'll probably replace it once or twice before I give up on that brand and return/exchange it for a Motocraft one. (that would be a lesson learned)
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Old 07-25-2013, 02:12 PM
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I unplugged the EGR valve, it did not set any Check Engine Light (CEL) but it did set some soft Diagnostics Trouble Codes (DTC) that I can read using the Android Torque application. MPG did not seem to be affected positive or negative.

The interesting side affect was that my IAT/IAT2 delta came back into spec, about 40. I tested this a couple times. Hook up the EGR valve and the IAT/IAT2 delta climbs back up to over 70 at times.

Now since, this is reproducible AND the temps drop to normal when the EGR is disconnected that leads me to believe that something in the engine systems that controls the EGR valve function is out of spec and is instructing the EGR valve to open pretty much all the time.
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Old 07-25-2013, 06:17 PM
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Overall, your numbers seem pretty normal. When the vehicle is cold <70*, the PCM will change parameters that will use more fuel until it warms up. It will still do it above 70, but you may not notice it as much. Shorter trips, and changing speeds will affect milage.

The IAT1 and IAT2 are a bit out of wack. As you suggested, your EGR may be staying open, or you are viewing it too early in the drive cycle. It is possible you need to clean the MAF/IAT sensor with MAF cleaner. As well, pull your EGR valve and clean it, even though it seems to close when unplugged.
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Old 07-26-2013, 04:06 AM
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My normal test track is 23 miles of interstate posted speed is 75mph and the IAT/IAT2 delta gets worse the farther you drive, eventually peaking with a 75-80 degree difference when the EGR is connected. Yesterday's temps were 65 (low) and 81(high).

The symptoms are present on short(distance) trips also. Yesterday I drove 12 miles through Fargo to Home Depot, first with it connected, which netted a 68 degree delta and then back to the work of other it disconnected and I watched the delta drop during the return trip back to a normal 40-42 degree difference.

I have only had this pickup for 3 months and had already pulled and cleaned the EGR and IAT2 about 2 months ago. I can dig up before and after pics if you'd like to see them. And as far as the IAT delta goes I don't view it so much as I log it and then go back later and analyze it. I can post those also.

My gut feeling is that I have a sensor, switch, or other component (ECM, EGR control module) that isn't functioning properly and running the motor in an opn loop when it should be closed. This EGR/IAT2 delta is just a symptom. I really think the EGR is functioning perfectly for the parameters that are being fed to it.
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