After changing the throttle and CAI ( https://www.ford-trucks.com/forums/1...er-my2003.html ) the P0171 check engine turned on. Only after the start, and not always. I checked with FORScan all parameters and problem is in Long Time Fuel Trim. Short Time Fuel Trim are lower than 5% plus or minus.

LTFT in bank 2 is correct too but in bank 1 always is more than 20% to over 35% and after that I have P0171 ( mixture is too lean ).







I'm sure that problem was before I changed throttle body and installed CAI but in lower range.

Where is problem ?? I think the problem is in the lambda sensor but maybe something else ??



After installed throttle body and CAI I canceled adaptation and made new one but problem is still the same.

 

If you have a plastic intake with aluminum coolant crossover, you may have a cracked intake. Or, you may have a bad intake gasket.

 

I have aluminium intake, I try to find some leak but everything looks ok. I check all conections and hoses. I have bifuel engine ( gasoline and LPG ) and the same problem is on LPG. I can modified map in LPG controller and go more rich with with bank 1 but it almost nothing change ( only in STFT ). When I run OBD adaptation in LPG controller STFT are correct but LTFT is the same like on gasoline.

I try to change lambda sensor from bank 1 to bank 2 and check it again. When it nothing change I try to find leak one more time.

 

I forgot that when installing LPG nozzles in the intake manifold, it was removed from the engine. Maybe it's really a bad assembly in the workshop.

 

could be. When you have lean code and it's as clear as it shows in your long term fuel trim, then it's most likely an air leak on one side of the intake.

 

Yes, you had right. I checked torque on intake manifold bolt. Near 2th and 4th cylinder I had to tighten because bolts were loose.

I done adaptation one more time and it's better.








I will drive few days and observe it. I think that bolts tightening is not enough and I need to change gasket... but which one is my.

 

Ok... after adaptation and next 100 km it is the same. Today I changed lambda sensor. Now its works ok when I drive with throttle but on idle FTFT1 goes over 25.

In my opinion when problem is in inlet manifold, should be all time. On idle underpressure is lower than on hi RPM but with throttle open LTFT 1 and LTFT 2 are the same. Why ??

 

Because the volume of air leaked into the intake at high rpm is very small when compared to the total volume of air being consumed.

The volume of air leaked into the intake at idle is much larger when compared to the small volume of air being consumed.

 

Maths, proportion, etc... ok.


Now, I must order gaskets, somebody help me?? :

4.6L engine, MY2003 with eight's digit W in VIN what mean Romeo but with aluminium block and full aluminium intake manifold ( 1L3E-9424-BA ). It's the same gasket like in plastic manifold ( 1L3Z-9424-BA ) ??

 

https://www.rockauto.com/en/catalog/...ld+gasket,5424

On Rockauto I see they list gaskets with "consolidated design", perhaps that means they work on both the aluminum and the plastic intakes? I can't say 100%, but since both types of intake bolts on to the same cylinder heads, they probably use the same gasket shapes.

 

Ok.

I bought gasket set ( lower and upper ). I spent few hours in my garage and I disassembly manifold.




Intake manifold and plenum were cleaned and checked. I cleaned cylinder heads surfaces too. After that I put new gaskets...



... and assembled everything.

But, after new ECU adaptation I have still the same.




What now ??

- lambda sensor replaced
- intake manifold gasket replaced
- injectors are good because the same problem is on gasoline injectors and LPG injectors
- STFT oscillate + / - 3 %


And new questions:
- Why if LTFT are extremely positive bad, STFT are good and not try be more positive to compensate LTFT ??
- Is were some other possible leak affecting only one bank ??

 

Ok.... problem solved !!!!!!!!!!!!!!!!!!!!!!!

I tried to find some leakage but nothing, nothing, nothing...

I read about some guy who has honda and mounted CAI and had high LTFT with normal STFT. Be checked vacuum line, MAF, lambda sensor.... and nothing, the same like my problem. He removed CAI and everything been ok.

I don't want to remove CAI but I think that here is a problem. I measured all inside diameters and:

Throttle body: old 2,6" new 3,0"
air pipe: old 2,8" new 3,4"

and I thought that maybe 3,4' diameter around MAF is too big, and more air flow goes outside sensor and maybe MAF not read proper values. I took silicon hose ( 3,0" ID/3.4" OD) and put it inside my CAI metal pipe before MAF sensor.






After start engine on idle STFT's imediatly goes to minus.



and after few minutes LTFT goes to correct values.



I one more time cleared old ECU adaptations and done new one. Now LTFT and STFT oscillates around zero.
I don't know why only first bank generate check engine, maybe manifold is not symetrical maybe something else, but I'm proud that I solved problem and my car again drive without errors.

 

Nice detective work. Thanks for the update on the resolution.

 

No problem. Next person with same problem can spent only 1$ not 101$ like me

 

Good job. Im having a similar issue but on a newer remanufactured engine. LTFT is 12.5 to 13.5 on B1. around 0 to 2 on bank 2. Drives me nuts watching it