I recently changed the stock muffler on my 99 f-150 5.4 4X4 to a 18" magnaflow. i few days later the computer threw up codes P0172 and P0175 (banks 1 ans 2 to rich) i read this with a autozone loaner and figured it was caused by the new muffler before the computer would relearn and reset the codes. Well now the light is back on, i havent checked the code but would bet it is the same as before. anyone else ever had this problem??? or could it be another issue. please help

 

Recheck your codes. I would bet it is coincidental, since a performance muffler would not cause a rich condition. Here's some things to check, got these from the Ford PCED manual. High fuel pressure, restricted air inlet, dirty air cleaner, or even leaking fuel injector(s). Kinda complicated, but you may have to take it to a shop, or if you are inclined, get a manual, and check out for yourself. It is time consuming, but a helluva lot cheaper than taking it to a garage. Good luck

 

Do this after every change you do to your truck:

1) Disconnect negative terminal on battery.
2) Turn on headlight switch, let sit for 10-15 mins
3) Turn off headllights
4) Re-connect negative terminal
5) Start truck, let idle for 3-5 mins
6) Drive normally for about 20 mins
7) Re-set your previous radio stations

This lets your computer re-learn your driving habits and any changes to your truck.

 

Did you bang and hammer in the system when making the change????

 

I had a shop do it, they used a sawz-all to take out the old one welded in the new one

 

Well i just went to autozone on my lunch break. I reset the computer before the weekend by unhooking the battery turn the headlights on. On my way to work this morning the CEL was back on and gave me new codes
P1132
p1152
p0175

I guess both upstream sensors are bad along with a to rich code
question: if these sensors are bad could that have thrown up the to rich codes originally on this post??
the sensors are pretty cheap at autozone (50 each ) but the real bummer is i was gonna do the whole 60,000 mile maintenance this weekend

fomoco, the mo stands for mo money

 

These codes do NOT mean you need new O2 sensors. They simply mean the engine is running very, very rich. It is unlikely that both pre-cat O2 sensors would go out at the same time.

Rich could be caused by a bad or dirty MAF, plugged fuel return line, bad Fuel Pressure Regulator, vacuum line fell off of the FPR, FPR diaphram ruptured, EVAP always purging, bad temperature sensor. That's about all I can think of off the top of my head. It could be the O2 sensors, but not very likely.

The first two codes refer to O2 sensor not switching. When running in closed loop (O2 sensors have fuel control), the computer will reduce the injection duration until the O2 sensor signals lean, the increase the injector duration until the O2 sensor signals rich, and so on. This occurs a few times a second and is so little rich and so little lean that the mixture is very close to the ideal 14.7:1. This switching from rich to lean to rich... is the only effective way to use this type of O2 sensor and it feeds the cat just enough of both HC and O2 to keep it warmed up. If the engine is running rich, the O2 sensors are stuck high (between 450mv and 1v) and is not switching.

Just re-read the original post. You could have knocked the evap canister vacuum lines or wiring loose while you were back there fooling with the exhaust. Another likely would be to have pinched or kinked the fuel return line. I'd look at these first, visual inspection. You can simply remove the vacuum line from the canister and plug it, see if the codes reappear to check the evap system. You can use a fuel pressure gage to insure you don't have a fuel return line plugged.