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5.4 Running Very Lean On Bank 1 and Rich On Bank 2

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5.4 Running Very Lean On Bank 1 and Rich On Bank 2

 
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Old 07-26-2018, 07:42 PM
Pooby88
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5.4 Running Very Lean On Bank 1 and Rich On Bank 2

I'm looking at a 2004 Expedition 5.4. It is running super lean on bank 1 (right bank). Fuel trim is at +30%. Bank 2 is running around -15%. If I do a KAM reset and set both banks back to zero it only takes seconds for them to return to their former numbers. I can not find a vacuum leak anywhere.

I used propane and sprayed it all over and around the intake manifold and it made no difference to fuel trim at all. I tried the same thing with carburetor cleaner, again no difference
Fuel pressure is good (30 psi).
There are NO misfires whatsoever (at least according to my scanner). Even using mode 6 I'm getting 0 misfires across all cylinders.
I flushed the injectors, made no difference
I pulled the air intake hose off and stuck my propane hose in it. I watched both banks go way negative, so my o2 sensors seem to be reading ok.
When driving,the only code that pops up is one for Bank 1 Lean

I'm running out of ideas
 
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Old 07-27-2018, 07:39 PM
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The cat is restricted on bank 2.
 
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Old 07-28-2018, 08:59 AM
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your reading data.......... what is the TEMPS at the CAT.
 
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Old 07-29-2018, 10:50 AM
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Originally Posted by 70f100longbed View Post
The cat is restricted on bank 2.

I guess that would help explain bank 2 running rich. BUT, why is bank 1 so lean? The only code I get is "Bank 1 Lean". No cat codes, no misfires, no codes related to bank 2 at all.
 
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Old 07-29-2018, 04:52 PM
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Because there is a difference in airflow between the banks but the PCM is using the MAF to determine injector pulse width.
 
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Old 04-15-2019, 02:40 PM
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Any answers yet?

Originally Posted by 70f100longbed View Post
Because there is a difference in airflow between the banks but the PCM is using the MAF to determine injector pulse width.

I'm having the same issue however it's a brand new motor has 500 maybe 600 miles on it. Ran fine for a week then started having this issue however this motor was put in with long tube headers and a non-catted y-pipe with tune deleted rear o2 sensors.
 
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Old 04-15-2019, 09:07 PM
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Originally Posted by 70f100longbed View Post
Because there is a difference in airflow between the banks but the PCM is using the MAF to determine injector pulse width.
This is distinctly the reason. One common mass air flow sensor is used to establish injector pulse width for two individual banks. One is breathing better than the other and the PCM balances the amount of air / fuel across the two banks based on O2 sensor input for individual banks separately.

The cause however, might be more than one restricted exhaust. If timing is off on one bank will cause this. Another possibility is one intake roller/follower being 'spit' out resulting in one intake valve not being functional. (I don't know that just one would make that much difference - but I think it possibly COULD.)

Just some thoughts.
 
 
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