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Edward
Edward, ASE Certified Technician
Category: Ford
Satisfied Customers: 2333
Experience:  ASE certified. Auto Transmission rebuilder for Ford Motor Co. from 91 to 2000
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ford f150: 2006 f150 4x4 5.4 at,bought truck at auction with

Resolved Question:

2006 f150 4x4 5.4 at,bought truck at auction with several miss fires changed all plugs and coils and ran good for a few months! now it misses and check engine light flashes when put under a load like going up a hill on the freeway but will not set a hard code, so i used a friends very expensive scanner with live data and everything looks good except if finds a fault [1] with the pcm, where do i go from here?
Submitted: 1 year ago.
Category: Ford
Expert:  Edward replied 1 year ago.
Hello and thanks for your question. My name is XXXXX XXXXX I will do all I can to help.

Let me first ask, What fault are you getting from your scanner? Does it set a code? If so, what code is it? just misfire codes? or any other codes?
Customer: replied 1 year ago.

no codes at all! it just struggles really bad under a load and check engine light will flash at that point but will not stay lit and runs fine when not under load

Expert:  Edward replied 1 year ago.
Alright, I understand. There are a few things I would check first, It's very possible it is the PCM, as the PCM does contain the coil drivers and grounds the coils at the precise time to fire the plug.

First thing you want to check is exhaust system back pressure, It's possible the cats are stopped up and you could have cylinders misfire because they can't breathe. This is a test that is done with a gauge that is screwed into the front O2 sensor port. If you have more than 2-3 psi of back pressure, then the exhaust sytem is clogged.

If you don't have a back pressure gauge you can use a vacuum gauge on the engine. should hold around 20 hg at 2500 rpm. if it's lower than that, could be exhaust clogged up.

Next thing to do, is use a scan tool to check your fuel rail pressure sensor , If it's showing low fuel pressure, (lower than 30 psi) I would replace the rail pressure sensor.

If all that looked to be alright, with your symptoms I believe you may have a failing PCM . But check those other items first. If it's just giving trouble when you throttle it up, It very well could be low fuel pressure or clogged exhaust.
Edward, ASE Certified Technician
Category: Ford
Satisfied Customers: 2333
Experience: ASE certified. Auto Transmission rebuilder for Ford Motor Co. from 91 to 2000
Edward and 11 other Ford Specialists are ready to help you
Customer: replied 1 year ago.

i think i checked the fuel pressure when i did the live data on the scanner it was fine, could i just take the o2 sensor out and drive it to check if it runs better?

Expert:  Edward replied 1 year ago.
Yes, you CAN do that, but I like a back pressure gauge to know for sure, because unplugging the front o2 sensors will set a code and it can make the engine not perform as well driving it that way. If it does it stone cold though after sitting, that is when I would do it to check it with the O2 sensors out, because PCM doesn't look at o2 sensor data until engine is warmed up anyway.
Customer: replied 1 year ago.

ok thank you!

Expert:  Edward replied 1 year ago.
Alright, Let me know if you have any further questions. You can always follow up with me later. Thank you.

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Edward
Edward
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ASE certified. Auto Transmission rebuilder for Ford Motor Co. from 91 to 2000