Need help diagnosing P0172 also random misfire codes (P0303, P0305, P0306)

[Summers22]

Bought this truck with 101k and zero maintenance has ever been done. It's a 2001 RWD flex fuel 3.0. Started on the maintenance items due to rough idle and failure to start at times. Runs pretty good now, but still has a rough idle once in a while. So far I have replaced the items below, but today, I have gotten a P0172 repeatedly after clearing it twice.

Tests so far include the dry fire injector test (turn ignition to start, hold down gas pedal, turn ignition to run) and the truck just cranks, let off gas pedal and it starts right up. I have seen that is a test for leaky injectors.

Inspected and sprayed brake cleaner near all vacuum lines, no change to idle speed.

Unplug IAC and truck idles down but still runs, plug in and it idless back up

Transmission fluid and filter - Wix filter & gasket and Motorcraft Mercon V fluid
IAC - Hitachi
Coil, sparkplugs, plug wires - all Motorcraft
Cleaned MAF and Throttle body - removed throttle body for this
Cam position sensor and Cam Synchronizer - Motorcraft
Air Filter - Wix
Fuel filter - Wix
Oil and filter - Pennzoil full synthetic 5W20 high mileage and Motorcraft filter
PCV - Standard Ignition
Coolant flush, new thermostat and temp sensor, both Motorcraft, Prestone antifreeze
Both upstream O2 sensors -Bosch

I have read to swap the 2 new O2 sensors with each other to see if the code switches to the other bank, to replace the upper intake plenum gasket, replace the MAF, etc. I just want to know what tests I should try using a nice scanner I am getting from my son tomorrow. I think testing STFT and LTFT tells a lot from what I have read, but I don't know how to interpret those results. All help is appreciated!

 

[Brain75]

the rich I wouldn't worry about it, it "sees" rich by noting any unburnt gas... well with a misfire you have unburnt gas so the 172 is just a natural byproduct of the 303/305/306 - all of those are misfires. Did you have any of those issues before replacing coil/plugs/wires? If not I bet you got a lemon in one or more of those parts.... even motorcraft (gasp).... I'd start by swapping back the wires (easiest - since I am lazy), and concentrate there swapping back to parts that worked before without issue. Once you get it all solved, clear codes, unhook battery for 20 minutes (to clear out all the memory that the IAC valve has set historically since you replaced that part) and then start up again and see what ya got.

 

[Summers22]

Thanks, but I dont have any old parts. I had a P0304 before replacing everything. I'll get the scan tool hooked up and watch for misfires and try and narrow it down to coil, plugs or wires.

 

[Summers22]

Looking back through my notes, 1 week ago I had a P0175 along with a P0303. I cleared those and they haven't came back. So those are both bank 2, the P0172 with P0305 amd P0306 are all bank 1, hmmmmm. I am not driving the truck much, just around the block a few times since its not tagged and has 13 year old tires on it.

 

[2011Supercab]

305 & 306 are bank 2

Passenger side is bank 1, cyl 1,2,3,

Driver side is bank 2, cyl 4,5,6

 

[Summers22]

Yes, so it looks like I am having misfires on both banks with both P0172 and P0175. I'll monitor MAF data this evening.

 

[Summers22]

Seems odd to have a P0172 (bank 1 rich) passenger side along with misfires for bank 2 driver side (P0305 & P0306). Then 5 days ago had the opposite with a P0175 (bank 2 rich) driver side along with a P0303 misfire cylinder 3 on the passenger side.

 

[2011Supercab]

Seems odd to have a P0172 (bank 1 rich) passenger side along with misfires for bank 2 driver side (P0305 & P0306). Then 5 days ago had the opposite with a P0175 (bank 2 rich) driver side along with a P0303 misfire cylinder 3 on the passenger side.

I'm kind of wondering if the O2 sensors are plugged into the wrong bank, wouldn't be the first time.

 

[Summers22]

? They were Bosch and the same part number, 15664. I replaced them through the wheel wells 1 at a time. Pretty basic to replace actually. I dont think the length of wires would allow for them to be plugged into the wrong side. This truck has bever had a single item besides the fuel pump replaced.

 

[Summers22]

Well got home and had to update and charge then scan tool. Decided to double check plugs and plug wires while letting the system reset by unhooking the battery. Checked all vacuum hoses again, decided to clean the MAF again and managed to break a wire in it somehow. No biggie, planned to replace it anyway. Also went to remove the EGR valve pressure sensor and immediately snapped a brittle nipple off into the hose. Removed both hoses and one had a bunch of gunk in it. So I decided to call it a night and go to town tomorrow for replacements.

 

[Summers22]

Update! Decided to go get replacements for the MAF and EGR pressure sensor. I also for the first time since doing all this work, disconnected the battery for a couple hours. Got everything installed, went through the relearn process at idle, let it idle for about 30 minutes all while monitoring live data, then ran a report. Went for a drive around the block 4 times and ran another report. Zero DTC's, no misfires, no injector faults, MAF was reading around 4.8 gps and it is running perfect!