Lean and Rich codes simultaneously - Ranger-Forums - The Ultimate Ford Ranger Resource

4.0L OHV & SOHC V6 Tech General discussion of 4.0L OHV and SOHC V6 Ford Ranger engines.

LinkBack Thread Tools Search this Thread
Old 02-26-2014
Thread Starter
Join Date: Feb 2014
Location: Bonnington, BC
Posts: 5
Lean and Rich codes simultaneously

I experienced a CEL accompanied with rough running and poor fuel economy starting about a month ago (in average -10C/14degreesF weather) with my 2006 Ranger 4.0l SOHC V6. I took it into Ford for a diagnostic and was reported back with P0174 Too Lean on Bank 2 and Misfire on Cylinders 1,2,3 and 4 codes. They also reported confirming the lean condition via scan data and furthermore seeing brake cleaner enter the intake when sprayed outside. The reported that power balance on the distributor seemed normal.

I conducted the following repairs in attempt to correct the problem


Set of 6 intake O-Rings
T/B Gasket
Spark Plugs and Wires
Fuel Filter


MAF Sensor with Sensor Cleaner (not sure if I did a good job or not)

I inspected for Vacuum leaks using propane torch and carb cleaner methods... as well as a rubber tube stethescope method hear the hiss noise... but in the end found nothing I could pick out and I am not confident because I have not found a good schematic of the vacuum system and componants for this engine. If anyone has one, please post a link... 2006 era V6 4.0 L SOHC, please and thank you

I did check the PCV elbow according to a previous post but haven't removed any vacuum hose for closer inspection to date, because I don't know what I'm dealing with and have a limited experience with vacuum inspection.

I bought a scanner yesterday and ran a few tests. The computer was reset inbetween yesterday. The codes brought up by the engine have been as follows:

p0174 Too Lean Bank 2
p0172 Too Rich Bank 1
P2196 O2 Sensor Signal bias/Stuck rich Bank 1 Sensor 1 (came up today after reset then went away)

Freeze data (today) as follows (at idle):

STFT B1 -4.7%
LTFT B1 -25%
STFT B2 +9.4 %
LTFT B2 +25%
STFT B1S1 -4.7%
O2 Sen Output B1S1 0.820V
STFT B1S2 99.2%
O2SensOutput B2S1 0.085V
STFT B2S1 9.4%
O2SenOutput B2S2 0.08V
STFT B2S2 99.2%
RPM 2535/min
Fuel Sys 1 Stat CL
Fuel Sys 2 Stat --
Calc Load 44.7%

Update: Driving home I noticed my live MAF air intake PID's reporting wild fluctuations even though my speed was constant at 60mph/100kph. eg. it would go from 1.4 to 4.8 lbs per unit. Is this metered by engine speed or vehicle speed? Could it indicate something?

Any leads would be hugely appreciated

Last edited by Aragorn 2006 4.0 SOHC; 02-27-2014 at 12:39 AM. Reason: update & correction
Reply With Quote
Old 02-27-2014
Thread Starter
Join Date: Feb 2014
Location: Bonnington, BC
Posts: 5
Well I've been getting some info on the BMW forum and the F150 forums. It seems Rangers aren't the only vehicles to throw Lean codes on one bank and rich codes on the other at the same time. I will have to try tomorrow and post a followup if I get any new info. I would want someone else to benefit from this someday, if I can figure it out.

Right now I have to get ready to take my girlfriend to a classical guitarist show. She's going to look really nice too. Hopefully my truck behaves!
Reply With Quote
Old 03-16-2015
Join Date: Mar 2015
Location: Watertown. MI
Posts: 1
Any luck?

Hi there. I was wondering if you'd ever solved this problem or just sold the truck. Thanks.
Reply With Quote
Old 03-16-2015
RF Veteran
iTrader: (1)
Join Date: Jan 2014
Location: Vancouver, BC
Posts: 7,582
Original post is over a year old.

If you are having a similar issue then I would post the symptoms in a new thread.

Lean and Rich codes are about the Oxygen in the exhaust not the fuel, many get confused on that point.

O2 sensors can only "see" Oxygen content.
Too much oxygen is Lean
Too little oxygen is Rich
Now if a cylinder misfires then none of the oxygen is burned up, so that oxygen is dumped into the exhaust system and O2 sees that as Lean, so computer adds more fuel to that bank, if cylinder starts firing again then no extra oxygen is in the exhaust so O2 would see too little oxygen since computer has added more fuel, so it shows Rich, computer reduces the fuel and maybe cylinder misfires again, so........back and forth, could be a dirty injector for that one cylinder.
That's just an example of possible issue.

If you think an engine is running lean or rich then pull out a spark plug, if it's black then it is running rich, if it is light brownish then mix is correct.

Last edited by RonD; 03-16-2015 at 01:27 PM.
Reply With Quote

Related Topics
Thread Thread Starter Forum Replies Last Post
Runs rich and lean? Rydogg311 4.0L OHV & SOHC V6 Tech 4 02-05-2013 04:33 PM
O2 Sensor / System too Rich Fault Codes, Seems to be running fine?? metallicamaster3 2.9L & 3.0L V6 Tech 1 12-23-2012 08:20 PM
Lean and Rich at the same time? stc5103 General Technical & Electrical 2 01-28-2012 11:05 PM
Running rich, codes p1131 p1132 flyinhawaiian SOHC - 2.3L & 2.5L Lima Engines 0 12-13-2006 09:59 PM

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

All times are GMT -6. The time now is 11:35 PM.

We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.