Hi All! Bit of a lurker so thanks in advance for looking! First of all, codes are below and the screenshots here are from my ODB2.

https://imgur.com/a/UU35IXS/

I’m trying to make a bunch of improvements to my 98 4x4 automatic and before I do it I wanted to try to solve a couple issues with my truck, namely seemingly low fuel economy. This opened up a few other issues I’d really appreciate some input on, alongside getting some input on the MPG situation, which I’d estimate combined to be 8 to 10. I am very inexperienced with most of this stuff but consider myself pretty resourceful and I have looked at previous threads about what to do for MPG, as well as fuel trim, how to use ODB2, etc etc. I’d rather fix whatever I can first but tend to hesitate with much of anything involving electricity or high pressure. I’m a baby.

So I just hooked up my OBD2 today. This was after driving to the grocery store and back with a little break in between, but temperature was in the normal operating range. Based on the attached screenshots it looks like my fuel trim numbers indicate I’m not running lean or rich (is this right?). I’ll be cleaning my MAF and replacing air filter, spark plugs and wires. I hope that will make some difference but I noticed the following when I pulled codes.

My auto shop was supposed to have fixed a 4x4 vacuum hose issue last summer but I see I’m getting an error there now. When I switch to 4x4hi I hear a noise but I’m not sure if it’s actually switching? It may have always been broken and I’ve never had or driven another 4wheeler so I’m not sure exactly what it’s supposed to feel like. I feel so naive! I clearly need to do more work on the 4x4 system and I’m just hoping my seemingly very nice and trustworthy auto shop didn’t take advantage of me on what they said was a repair of that system.

Otherwise, anything else I should be thinking about here? Thank you so much. I’ve googled these codes and everything but I am a noob. I don’t have a check engine light and other than the MPG my truck runs great so I don’t really know how to interpret much of this but want to try before I get it repainted, install accessories, etc.

===OBDII DTC None=== Successful DTC reading, no error codes found

Module: On Board Diagnostic II

===END OBDII DTC None===

===PCM DTC None=== Successful DTC reading, no error codes found

Module: Powertrain Control Module

===END PCM DTC None===

===IABM DTC None=== Successful DTC reading, no error codes found

Module: Integrated Air Bag Module

===END IABM DTC None===

===GEM DTC P1878=== Code: P1878 - Transmission Transfer Case Disengaged Solenoid Circuit Failure

Module: Generic Electronic Module

Diagnostic Trouble Code details

Transmission Transfer Case Disengaged Solenoid Circuit Failure

===END GEM DTC P1878===

===GEM DTC B1622=== Code: B1622 - Rear wiper low limit input circuit short to ground

Module: Generic Electronic Module

Diagnostic Trouble Code details

Rear wiper low limit input circuit short to ground

===END GEM DTC B1622===

===GEM DTC C1752=== Code: C1752 - Vehicle Speed Sensor #1 Circuit Failure

Module: Generic Electronic Module

Diagnostic Trouble Code details

Vehicle Speed Sensor #1 Circuit Failure

----------Possible Causes---------

VSS #1 Output Circuit Short to Ground

Circuit wiring concern.

Water in connector.

Internal module concern.

Short in VSS.

===END GEM DTC C1752===

===GEM DTC C1751=== Code: C1751 - Vehicle Speed Sensor #1 Circuit Failure

Module: Generic Electronic Module

Diagnostic Trouble Code details

Vehicle Speed Sensor #1 Circuit Failure

--- Possible Causes --------

Somewhere in the harness/circuit/connector there is a short between the Vehicle speed signal and Vbatt.

-Suspect Vehicle Speed Sensor Vehicle Speed Harness Wiring or Connector.

===END GEM DTC C1751===

===RAP DTC B1522=== Code: B1522 - Hood switch circuit failure

Module: Remote Anti-Theft / Personality Module

Diagnostic Trouble Code details

Hood switch circuit failure

--- Possible Causes -------- This DTC can be generated by:

-Ground Short Hood Open Switch

-Suspect Lighting Control Module

===END RAP DTC B1522===

 

Upon additional research, looks like the P1878 error only means 4x4 isn't engaged at the moment. I drove around the block a few times and switched 4x4hi on and the error code didn't go away when I refreshed. Still thinking of ideas...

 

Welcome to the forum

1998 Ranger 4x4

You have Pulse Vacuum hubs(PVH) on the front wheels, Ford dropped these as soon as possible because they didn't work very well
You should change to Manual hubs, AVM makes the manual hubs, they are sold as AVM, Mile Marker or Rugged Ridge

If you want to try and repair the vacuum hubs read here: https://www.therangerstation.com/tec...pair_tsb.shtml
Its for sure a temporary fix as these just didn't work long or well, lol

AVM swap seen here: https://www.therangerstation.com/tec...hub_swap.shtml


Your engine wouldn't run at all under 10MPG, so there is a problem with the calculations you are doing
If you don't have the stock tire size on the Ranger then Odometer is not correct, so you can't use to calculate miles traveled
Speedo/odo is calibrated at the factory for stock tire size
Larger diameter tires show lower miles on odometer than actually traveled, and lower speed on speedometer than actual speed

O2 sensors need to be changed every 12 years or 100k miles to keep MPG where it should be on any vehicle, not a Ranger or Ford thing, O2s just run out of chemicals to detect oxygen


Fuel trims are open times for injectors
Computer calculates injector open time based on engine size(like 3 liters or 4 liters), RPM, throttle position, air weight(MAF), and air temp
That calculation is STFT 0
Says thats 100ms(milliseconds) open time for each injector
Computer then looks at O2 sensor voltage(0.1v to 0.9v) it wants to see 0.4volt
If it sees 0.2v(lean burn) is adds more fuel so open time changes 102ms so STFT +2%, is its a %
If it see O2 voltage of 0.6v(rich burn) it reduces amount of fuel, open time 98ms, STFT -2%

All done on the fly and within 1 second, its very very fast in responding to O2 sensor voltage changes
STFT from -5 to +5 is normal when cruising, when accelerating it can go +10 to +20

LTFT is long term fuel trim
This is used so computer doesn't have to re-learn the system every time you drive it
New vehicle will have 0 vacuum leaks and 60psi fuel pressure, also perfect EGR system, EVAP system, and good gasoline, lol
10+ year old vehicle will not have everything new and perfect

As a vehicle ages there will be some small air leaks, a bit lower fuel pressure, ect..............
LTFT is an average of STFT that the computer saves in memory for the next startup
Say there was a small vacuum leak and STFT average was +5, then LTFT would be saved as +5

If LTFT is +5, then computer does its calculation and then ADDS LTFT to that, and thats the new STFT 0
So this STFT takes into account any small changes in the whole system so computer doesn't have to re-learn it each startup
If you fixed the small vacuum leak then STFT would go to -5 average over the next few drives and LTFT would come back down to 0
There is a bit more to it but its the concept of what going on that I am explaining