5.4 l check engine light
10-09-2015, 05:21 PM
#1
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5.4 l check engine light
I have a '10 with the 5.4. Truck has 79000kms and last week the check engine light came on. Codes show that both left and right banks were lean. Plugs have been changed, MAF was cleaned, vacuum test and fuel pressure test show no leaks. After 11 cycles of the ignition, engine brought to running temp three times and diagnostic shows all the numbers are within the parameters. I took it for a ride and had the ignition turned off twice......the light is back on. What else could it be? Thought O2 sensor but two failing at the same time for both banks to show lean???? Any thoughts or similar experiences?
10-10-2015, 12:10 PM
#3
LightningRod
Some thoughts
@Shoe66; Specific codes would be more helpful than hoping you haven't just diagnosed a lean situation from some other sources, but I presume you mean you have P0171 and P0174 codes.
The meaning of 171 & 174 is pretty clear, (the PCM is getting "too lean [< .45v]" readings from UpStream O2 sensors after it has already adjusted injector pulse width 'Fuel Trims' to the max specified limit [>25% to 30%]), but these codes can have a wide assortment of causes and source points. Some you indicate have been checked - but didn't mention HOW or how carefully they were checked. I think you have "unmetered or improperly measured intake air" entering the combustion process.
There is and EXCELLENT write-up on this very problem by @02RedScroo at this link: http://www.f150online.com/forums/v8-...171-p0174.html
As 02RedScroo states, it is ALMOST imperative that you have a scanner that will give "live data" readings and/or graphs, and read "Freeze Frame" data. He provided a link to an inexpensive one at Amazon in his thread. I use the Torque Pro App ($4.95) and a bluetooth adapter off Ebay or Amazon for less than $25.00. But you need to monitor fuel trims and O2 readings/graphs while checking for vacuum leaks as O2RedScroo instructs in detail. I believe you have correctly determined it is NOT likely TWO simultaneously bad O2's. My 5.4l had a crack in the Intake Manifold found by monitoring O2 graphs while spraying starting fluid (ether) under the intake manifold.
A couple of things 02RedScroo did not mention is to monitor live fuel trims at different RPM's. (a small vacuum leak will effect fuel trims MUCH GREATER at low RPMs (because the ratio of unmetered air is much lower at higher RPMs). An exhaust leak (ahead of the Upstream O2's) will cause higher fuel trims during operating conditions that would be invoking maximum Cam Retard for EGR effect (light load at cruising speed). [This however is much less likely since you have BOTH banks indicating lean]. You can get more information pointing which way to look (such as RPMs / Speed) by studying Freeze Frame Data - captured at the instant the DTC is set.
You mentioned cleaning the MAF - (and it would definitely be suspect as a source common to both banks) but it's hard to determine if it is producing the correct reading without a scanner. According to my Factory Service Manual (table of diagnostic reference measurements) the following might help. PCM pin B40 should be the plug nearest the passenger fender - IF THE DAMN MANUAL IS CORRECT. I do notice the Schematic indicates the wire goes to pin 43, not 40 ???? So rely on this info cautiously. But you can pin the MAF wires at the MAF and find the signal wire and it might give you some idea. But better - GET A SCANNER!
Sensor___ PCM Pin__ KOEO__Hot Idle____ 30 MPH____ 55 MPH____ Units
MAF________ B40 ___ 0.01 _ 0.71 _______ 1.31 _____ 1.87 ____ VOLTS
Finally, after changing anything out, its a good idea to do a "battery reset" and go through a "relearn" process.
Good luck
The meaning of 171 & 174 is pretty clear, (the PCM is getting "too lean [< .45v]" readings from UpStream O2 sensors after it has already adjusted injector pulse width 'Fuel Trims' to the max specified limit [>25% to 30%]), but these codes can have a wide assortment of causes and source points. Some you indicate have been checked - but didn't mention HOW or how carefully they were checked. I think you have "unmetered or improperly measured intake air" entering the combustion process.
There is and EXCELLENT write-up on this very problem by @02RedScroo at this link: http://www.f150online.com/forums/v8-...171-p0174.html
As 02RedScroo states, it is ALMOST imperative that you have a scanner that will give "live data" readings and/or graphs, and read "Freeze Frame" data. He provided a link to an inexpensive one at Amazon in his thread. I use the Torque Pro App ($4.95) and a bluetooth adapter off Ebay or Amazon for less than $25.00. But you need to monitor fuel trims and O2 readings/graphs while checking for vacuum leaks as O2RedScroo instructs in detail. I believe you have correctly determined it is NOT likely TWO simultaneously bad O2's. My 5.4l had a crack in the Intake Manifold found by monitoring O2 graphs while spraying starting fluid (ether) under the intake manifold.
A couple of things 02RedScroo did not mention is to monitor live fuel trims at different RPM's. (a small vacuum leak will effect fuel trims MUCH GREATER at low RPMs (because the ratio of unmetered air is much lower at higher RPMs). An exhaust leak (ahead of the Upstream O2's) will cause higher fuel trims during operating conditions that would be invoking maximum Cam Retard for EGR effect (light load at cruising speed). [This however is much less likely since you have BOTH banks indicating lean]. You can get more information pointing which way to look (such as RPMs / Speed) by studying Freeze Frame Data - captured at the instant the DTC is set.
You mentioned cleaning the MAF - (and it would definitely be suspect as a source common to both banks) but it's hard to determine if it is producing the correct reading without a scanner. According to my Factory Service Manual (table of diagnostic reference measurements) the following might help. PCM pin B40 should be the plug nearest the passenger fender - IF THE DAMN MANUAL IS CORRECT. I do notice the Schematic indicates the wire goes to pin 43, not 40 ???? So rely on this info cautiously. But you can pin the MAF wires at the MAF and find the signal wire and it might give you some idea. But better - GET A SCANNER!
Sensor___ PCM Pin__ KOEO__Hot Idle____ 30 MPH____ 55 MPH____ Units
MAF________ B40 ___ 0.01 _ 0.71 _______ 1.31 _____ 1.87 ____ VOLTS
Finally, after changing anything out, its a good idea to do a "battery reset" and go through a "relearn" process.
Good luck
Last edited by F150Torqued; 10-10-2015 at 05:41 PM. Reason: add last sentence - afterthought