Long Term Fuel Trim Bank I Ford Ranger issue.

2008 Ford Ranger , automatic V6 vulcan engine. LTFTBank 1 at idle is negative .8% LTFT Bank 2 is 9 % at idle. Drive down the highway both LTFT Bank 1 and Bank 2 are within limits, but take foot off gas pedal LTFT Bank 1 drops to negative .8% and LTFT Bank 2 reads about 8%. It almost seems like the computer is not learning the LTFT for Bank 1 - does anyone have any suggestions or ever seen this before?

Check Bank 2 for a vacuum leak.

When Total Fuel Trims are under 10%, which is your case, it can be difficult to find problems.

0.8 at idle for Bank 1 is good, but if bank 2 is going from 8 to near zero when you step on the throttle, that is indicative of a vacuum leak.

Or are you implying your bank 1 trim does not move at all? You verified you are in closed loop?

Use a propane torch with a long rubber hose attatched to it and allow some propane around the intake and injectors of bank 2 at idle, does the short term respond by subtracting fuel?

It might be worthwhile to see if all the O2's can respond to Rich/Lean conditions. While watching live data snap the throttle three consecutive times, all the O2's should switch Rich/Lean ( 0.1 volts to 1.0 volts) for both bank 1 and 2.

Thank You for the response. LTFT Bank 1 at idle is negative .8% Long Term Fuel Trim Bank 2 at idle is 9%. When you drive the truck, both long term fuel trims are within limits. When you take your foot off the gas and also when you stop the truck and idle, this is when the Long Term Fuel Trim Bank 1 drops to negative .8% and Long Term Fuel Trim Bank 2 is at 9%. Just a guess on my behalf , it looks like the computer is not "learning " the LTFT on Bank 1.

bills4065 wrote:

it looks like the computer is not "learning " the LTFT on Bank 1.

What does the total fuel trim indicate?

Long Term Fuel Trim Bank 1 while driving: LTFT 6.3% STFT 3.1% for a total of 9.4% Fuel trim while driving the vehicle. The only time bank 1 LTFT goes to negative .8% is sitting idling or taking foot off the gas while driving ie. deceleration. Just thinking out loud here, would a Bank 1 cat converter starting to go bad cause something like this? There are no cat codes.

A clogged cat would give you a negative trim.

Have you tried resetting the KAM ( Keep Alive Memory)?

Disconnect the NEG battery cable, cover the post and use a jumper wire between the NEG cable and the Positive cable. DO NOT LET THE NEG CABLE TOUCH ITS POST OR GROUND ANYWHERE.

This will drain all the capacitors and any memory in the PCM, then see you will start with fresh trims and go from there.

@ Paul P- Thanks for all the info , I will try that. I will also contact the friend with the ranger that has this problem and I will take it out and do a wide open throttle run and see what the two upstream O2 sensors are reading at wide open throttle. I will post back my findings on these checks , may be a couple days until I can check this for him.

You want to see the upstreams switching rich/lean regularly while cruising.

Once your warmed up, 3 consecutives "Pedal to the Metals" should get the rear O2 to switch as well.

On a cruze its normal to see every approx. 20-40 switches of the front O2 to see a rear O2 switch.

Main thing, prove ALL the O2's are switching Rich/Lean.

well, got a chance to look at this again today. This time there was a code PO420.
I took the truck for a highway run to check cat temps and there were both around 780 celcius, I realize this does not tell me catalytic converter might be getting plugged. he said gas mileage was terrible , so I wanted to take a look at his air filter, popped off filter box cover and filter box half full of straw , grass, etc. Cleaned it all out and he is going to see how it is working now. Air restriction could cause rich condition for sure, but does it make any sense only affect bank 1?

could this be some kind of p2297 I would maybe look at mode 6

try closed pedal acceleration control strategies in computer

well, graphed the bank 1 upstream and downstream oxygen sensors on this today and the downstream sensor mirrored the upstream sensor throughout the 15 minute drive, so I am thinking the catalytic converter on Bank 1 is no good. The Long Term Fuel Trim on Bank 1 is now 2.5% and Bank 2 is 12.5%. I told my friend get the # 1 catalytic converter replaced before I do anything else with this. The PO 420 code was also back on before I took it on the test drive,

Good Call. This is solid evidence of the cats inability to perform its chemical function.

You might be repairing the first of possibly multiple issues.

Good work!

this owner is aware of converter issues, but is going to get a price on body work rust to see if vehicle is worth fixing.

The owner was informed rust damage extensive on this truck, and was parted out. The number 1 bank on this truck catalytic converter oxygen sensor was mirror image of upstream oxygen sensor, thus the PO 420 code. It was probably partially restricted as well. Just wanted to update what happened here.