New 5.0L built, low compression and horrible MPG

[1997XLTRollover]

In theory any leaks after the front O2 sensors, wont effect the way the vehicle runs. That's because the rear O2 sensors are only for setting catalyst efficiency codes, they don't even effect fuel trims.

The front O2's, they are a different story. Any leaks before them will cause air to be drawn into the exhaust system and those O2's will report a lean condition. The PCM will then add fuel and there goes your fuel mileage down the toilet.

While I'm driving my fuel trims are anywhere from 2-3% or 4-6% depending on throttle and load. Idle and cruise seem to be ok and only adding 1-2%. I'm so lost with this thing. I should probably do a leak down test and see how that comes up. I wish I had a set of stock tires and wheels to put on it.

 

[4pointslow]

Fuel

You might want to try testing your fuel. The higher the ethanol content the worse the fuel mileage.

Fuel trims sound perfect.
Cylinder leakage usually only needs to be performed if compression is low, but it would not hurt to at least have the results for future references.

 

[1997XLTRollover]

You might want to try testing your fuel. The higher the ethanol content the worse the fuel mileage.

Fuel trims sound perfect.
Cylinder leakage usually only needs to be performed if compression is low, but it would not hurt to at least have the results for future references.

I've been running the same shell fuel from the same station for 10 years. Plus my 99 ran the same fuel from that same station and managed 19mpg.

 

[4pointslow]

gas

Gas stations change the amount of ethanol in there fuel, it is common.

 

[1997XLTRollover]

Gas stations change the amount of ethanol in there fuel, it is common.

True but this is shell, and none of my family has fuel mileage problems. I also know the guy who owns the station so it's not a shady place. I suppose I can try a different station and see if there's change but I'd be shocked. People around here always say they get the best fuel mileage from this shell station. I wish I knew someone with stock wheels because I'm dealing with too many possible variables too. 32a and headers which may hurt bottom end. I also want to check exhaust backpressure like you suggested.

 

[beach]

Your patience...... I would have Dexter'd someone by now

 

[1997XLTRollover]

Your patience...... I would have Dexter'd someone by now

I'm about there. Very. Very close. To knocking out the next person who looks at me funny. Lol

 

[4pointslow]

vehicle

when was the last time you drove the Explorer that got good fuel mileage?

 

[1997XLTRollover]

when was the last time you drove the Explorer that got good fuel mileage?

Before winter gas hit. Sold it end of last year.

 

[beach]

I'm about there. Very. Very close. To knocking out the next person who looks at me funny. Lol

Have you ever done a radiator on a 5.0? When I did mine, I wanted to track down the engineers at Ford and murder them... slowly... one by one lol

 

[1997XLTRollover]

Have you ever done a radiator on a 5.0? When I did mine, I wanted to track down the engineers at Ford and murder them... slowly... one by one lol

Yes. On my 96. Twice.....

 

[4pointslow]

Diagnostics

I am out of ideas from off the top of my head.
For what its worth here is the diagnostic flow charts for poor fuel mileage, maybe they will help.
Note DSR1 is checking for DTC's.
DSR20 is third picture.

 

[1997XLTRollover]

Well **** me. Spoke too soon. CE light came back on. Same P0446 code. Maybe I still have a chance of this being my fuel economy issue. I'm about to throw in the towel. I don't know what else to check. I guess the only other thing I can do is smoke the system right from the intake manifold which I didn't do last time. I just don't want some $500 bill from a shop to fix a truck I paid $500 for originally.

 

[1997XLTRollover]

Looking at the Ford PC/ED for engine diagnostics I see some typos. So I must have looked at the description given by your scan tool that says open or shorted circuit and thought the code was P0443 which can only be set by circuit problems. I must be getting old. lol.

The code you say you really have P0446 links to a pinpint test that says it is for P1450. I then looked at the same code for a 1997 and found that the pin point test is for P1450 and P0446. Sorry for the confusion.
Here is the first Pin Point test for P0446, it can be caused by vacuum leaks, bad vent valve, purge valve, fuel tank pressure sensor, or cap loose/off etc.

Ok so my check engine light turned off for a bit after I got irritated and flew out of my pothole infested driveway this weekend. It then came back on today. I'm starting to think that this EVAP is an intermittent issue due to a loose connection or wire because of that and how my fuel gauge will randomly act up. It seems to happen when I come to a stop or accelerate hard which made me think it was the sending unit but I'm wondering now if it's a wire.

Is there anything that would be tied to the fuel gauge that would also effect the EVAP system? Is the pressure sensor on the same harness as the sending unit or is it somehow related in the cluster or anywhere else?

 

[4pointslow]

Fuel gauge

At this point anything is possible. Intermittent problems are a pain to diag too.
I think I posted the wiring diagram for the fuel gauge, and the evap solenoids.
You can look at them to see if they are related or not.
If I did not post both let me know, or if you need a diagram of something else.

 

[4pointslow]

Pressure sensor

Here is the pressure sensor diagram.