My sitch is this:
My 5.4L-based stock E350 with Auto, stock tires was giving me an average of 16 mpg (low 12, high nearly 19) after 16,000 miles of tracking across the country (literally) (I did the filling consistently and computed manually). Last year I did a custom 4X4 straight axle conversion, kept the stock tires/wheels, and still got the same avg MPG for the first 3,000 miles. Same mpg computations/filling. The 4X4 did not impact mileage but a smidgen. I know that for sure.

After 3,000 miles the mpg dropped significantly and continued to degrade. No physical changes to the vehicle.

It seemed to begin about the time I did a 10,000 mile trip into Canada. Thinking it was bad gas, I replaced the fuel filter after returning, air filter change twice. No change in mileage; actually getting worse.

Some research suggested a MAF sensor cleaning. It was covered with a crusty black stuff. The MAF cleaner made it all shiny again. I also bought OBD II software and cable and logged some data before and after cleaning. It appeared the fuel trim got better, and the mileage gained some, but it continues to be a lot less than my good readings.

So, what I have now is about 600 miles of logged OBDII data of all sensors after initial testing and logging short jaunts plus a 600 mile trip on which I logged the entire time down I-5 (flat valley followed by up and down hills) and across the southern Cascades (hills again).

What I'm looking for is the process of how to digest this data and what I should expect to see for fuel trim, MAF (lb/min, not volts), oxy sensors (though the oxy sensors seem to be reading okay from 1. to .9 volts), etc. I have a lot of data and don't quite know the correlation and expected values and what unexpected values might point to.

The vehicle has 128,000 miles on it (I bought it with 78,000 two years ago). It was an air force van, so I assume it was consistently maintained on the base. It's a 2004 E350 with 5.L, auto, no mods (except the 4X4), and I'm well aware of driving habits on mileage. I drive consistently, so I wouldn't expect such a dramatic drop in mileage. Fuel filter is new, air filter is new, existing plugs, wires, injectors, etc. Oil changes every 3-4k miles. Serpentine belt is good. No codes whatsoever. As I said, the physical configuration (inside and out - considering air drag effects) is consistent from good mileage to bad.

I'm considering plugs, wires, and injectors replacement since those could be original or at least 50,000 miles old. But I don't want to throw out money on an unknown. Any recommendations greatly appreciated.

TIA

 

Despite claims made plugs will last 100K miles those of us driving modular motors know better---50K at best so right off I'd strongly suggest changing those ASAP, boots too (NAPA/Belden 702418). Using the Ford/Motorcraft called out for your year/model/engine but I'm guessing SP-479's. Don't play around with other brands although Autolite are acceptable substitutes. Of course I'm assuming you've never done this...............

Follow the recommendations found here: https://www.ford-trucks.com/forums/1...ed-torque.html, post #2

I'd also recommend good grades of gas, add a bottle of Techron occasionally and keep your MAF clean too---all just part of maintaining acceptable MPG's.

Best of luck!

 

Thanks, JWA for recommendations and link. Plugs, wires, etc. will be next.

Any recommendations on guidelines for interpreting my collection of data?

 

Thanks, JWA for recommendations and link. Plugs, wires, etc. will be next.

Any recommendations on guidelines for interpreting my collection of data?

 

Bob I'm far from an expert or even knowledgeable amateur at codes etc but if you show none and none pending any potential repairs etc would be a guess.

I have to think since you don't mention codes or the CEL being illuminated the ECM isn't picking anything up, not within its ability to do so. My guess is changing the plugs will reveal something.....................

 

Mass air flow should be engine displacement at Idle no load . 5-6 grams per second on a 5.4 Wide open throttle under load should be around 200 gps . Fuel trim should be +or -5% . long term . o2 should toggle rapidly . If your fuel trims are over + 5 or so you are running lean, computer adding fuel . Under -5 or so running rich , computer removing fuel .

 

JWC you seem to know your do-do on this---care to take a shot at interpreting my data?

2003 Ford E-250 L = 5.4

Record Data

FRAME: -1 TM: -2.2

MIL STATUS Off
ABSLT TPS(%) 29.0
ENG SPEED(RPM) 2048
CALC LOAD(%) 50.2
MAF(LB/M) 5.96
COOLANT(°F) 189
IAT(°F) 50
IGN ADV(°) 33.5
ST FTRM1(%) 2.3
ST FTRM2(%) 0.8
LT FTRM1(%) 0.0
LT FTRM2(%) 0.0
VEH SPEED(MPH) 66
FUEL SYS 1 CLSD
FUEL SYS 2 N/A
O2S11(V) 0.120
ST FTRM11(%) 2.3
O2S12(V) 0.775
O2S21(V) 0.820
ST FTRM21(%) -3.1
MIL DIST(mi) 0
OBD2 STAT CA


This is from my Actron CP8590 scanner during a recent test drive.

Interested to see what its telling me.

 

Bank 1 and 2 fuel trims are skewed . Loks like there may be a lean issue on bank 1 , but your downstream b1 is close to b2 . Could be a vac leak or sluggish o2 b1s1 .I don't have a converson handy for lbs to grams , so I cant work with your maf . Do you gave graphing capability ? You can get a better picture while graphing an comparing . If your down streams are hanging close it could be an upstream o2b1 . I would want to see more data before condeming . Maf in gps and not just 1/4 throtle numbers .

 

Thanks JWC 3----interesting but I'm still learning about much of this stuff.

I have a few more frames of recorded data but looking over the numbers I was driving on the freeway so TPS and so on are pretty much the same for all of them.

I'll check my scanner's capabilities, see if the graphing can be done. Any recommendations on how I should test drive to better cover what the scanner is recording?

 

Ck at cold idle and warm idle . That will help show cold vac leaks . Ck normal drive and full throtle . That will help show fuel delevery issues . If you can't graph watch live data while someone else drives . I do recomend a graphing scanner . Launch sells some good inexpensive ones . OTC has a good one also . Others out there . Ck AESwave.com for some ideas .