Chasing causes of large fuel trim

[jastutte]

My OBD-2 scanner is giving me some far out numbers on fuel trims. This started before I recently replaced my Y-pipe and hasn't changed since. These are the numbers I'm getting:

Short term trims, sensor 1: ranging from -3 to -12 across a range of conditions.
Long term trims, sensor 1: ranging from -3.9 to -5.5.

Short term trims, sensor 2: ranging from -2.3 to -10.
Long term trims, sensor 2: -3.9 to -5.5.

Short term trims, sensor 3: -25 to -30.
Long term trims, sensor 3: -26 to -28.

Short term trims, sensor 4: -24 to -30.
Long term trims, sensor 4: -25 to -26.

My scanner doesn't tell me which sensor is which (i.e. upstream, driver's side), the manual doesn't either. I have a Bluetooth ELM27 OBD-2 dongle on the way I'm going to hook up with Torque Pro to get a more useful readout.

In my research on DiscoWeb and elsewhere I saw mention of other possible culprits, including fuse 3 under the steering column (was fine) and faulty MAF. Here are some data ranges from my scanner during a test drive last night. Again, I don't know what the units are or what range they should take.

• 0.17 - 0.20 at 25mph, 1,000-1,200rpm
• 0.45 - 0.55 at 60mph, 2,400 rpm

If my MAF was faulty, wouldn't that affect the fuel trim on both banks?

Recent work done:

• new Y-pipe and gaskets
• new driver's side upstream O2 sensor (NGK/NTK)
• reconnected loose wiring on car side of same sensor connector plug

Not so recent, but also done:

• new fuel pump
• new fuel pump wiring harness
• new O2 sensors on passenger side

I'll probably get some better data with better tools - my scanner is not the greatest - but until then what are some other things I should be looking for or testing to track down causes of my large fuel trim numbers?

aren't sensors 3 and 4 typically the rear sensors? 3 being driver's side rear o2 sensor and 4 being the passenger's.

 

[Tugela]

Seems super rich. Check coolant tempt sensor and wiring to it. I would unplug the battery and hold both positive and negative together for at least 10 minutes. That drains all the internal capacitors in ecus and wipes out memory. Start fresh and see what returns

This sounds like an invitation for unintended consequences. I'm leaving tomorrow on a 700-mile road trip and don't want to cause other problems right before departure.

 

[_ExpeditionMan]

use RobertF's GEMS tool and reset the adaptive values. No downside and I'd be willing to bet a little bit that it works to solve your problems.

Where would one find this tool?

 

[Tugela]

Where would one find this tool?

It's an app for Android, I believe it's available on Google Play store. You need an Android device and ELM27 bluetooth OBD-2 dongle.

EDIT: tried the 10-minute crossing of the wires (against the advice of Dr. Egon Spengler) and didn't see any change in the data. Nothing look like it reset, except for my radio.

 

[WaltNYC]

Here is the thread.

Reset adaptive values

Ah, gotcha. That makes total sense, and I really appreciate the explanation. I went ahead and bought the ScanTool since the GEMSFixer already works with that tool. Should be here in a few days. Thanks again for your help with this! Cheers! Alfredo

discoweb.org

work from latest to earliest....it is 13 pages long.

software:

GEMS ECU Utility for Land Rove - Apps on Google Play

Land Rover adaptive reset and immobilizer utility for GEMS based vehicles

play.google.com

recommended OBD dongle:

https://www.amazon.com/dp/B00H9S71LW/?coliid=I26H4EQKAA8K74&colid=3SZYBJV1LFLYW&psc=1&ref_=lv_ov_lig_dp_it

 

[Stocksuspension66]

This sounds like an invitation for unintended consequences. I'm leaving tomorrow on a 700-mile road trip and don't want to cause other problems right before departure.

Not at all. You ever do a hard reset on on your phone? I would feel more safe doing a hard r reset than using an un-approved diagnostic tool for more than just code reading. Safe travels and hope all is well.

 

[Tugela]

Update: I connected the cables as suggested but didn't see any noticeable kind of reset in the data when I began driving again.

On the 700-mile trip I saw the fuel trims on sensors 3 and 4 improve slightly. They were about -23 over the course of the journey. A pleasant surprise was my fuel economy. I got 18mpg+ and made the trip on less than two tanks of gas. I've never seen this kind of consumption on my Disco before. Had plenty of power through the mountains and held a steady 65-70 mph most of the way. Removing the brush bar and roof rack in advance helped. I had a couple hundred pounds of gear in the back and tires are 245/70/16 AT.

 

[Tugela]

I finally updated my scanner setup and acquired the recommended combo of the OBDLink LX Bluetooth dongle and Torque Pro for my Android phone. I haven't fully configured Torque or explored it in depth, but I did set up a custom dashboard to get a feel for it. I also bought a cheap Android 7" tablet as a dedicated unit to keep in the Disco for this purpose (and to store a copy of RAVE). I noted the app allows you to display fuel trim by bank in addition to/rather than by individual sensors (as well as for permutations of sensors beyond those I actually have). My long term trim on each bank was -1.6. I'm okay with that. For stretches of my recent road trip that figure was at zero.

I'm curious if my previous, more basic model scanner was showing data for the downstream sensors in a way that numerically may have been correct, but in the context of their function was meaningless. Does it matter if the long-term fuel trim readouts for the downstream sensors was -26? Maybe those were data points I should have been ignoring. Returning 18+ mpg on a 1,400-mile road trip seems like good performance.

So maybe I made a fuss out of nothing. Maybe there's still something there I need to figure out once I get the hang of the new tools.

 

[4Runner]

18mpg is nothing to complain about for sure. 14 is always where I seem to be no matter whIch management system is in charge of the motor. Lol Remember that you are still using the same amount of fuel you always have, it’s just how the ECU is accomplishing that. Things won’t start to go poorly until the ECU has to step outside of the window allowed for that particular adjustment. But them you will also get a CEL. I would probably just monitor that for a while and see what happens.

 

[Harv]

18 mpg, from your location I'm assuming US gallons. That sounds really good. I have a hard time getting 18 mpg Imperial.