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Running rich?

01 Taurus, 180k, Vulcan motor

  1. Original plugs? Misfire. Huge gap. Installed new plugs.
  2. 1 month later , new timing cover gasket, immediate #3 misfire
  3. New coil, misfire is gone
  4. Next day, got 0171 and 0175 code. Bank running rich
    Is new coil weak? Suspect? Did misfire affect cat performance?
    Only driven 10 miles with new coil

“Rich” is not an ignition problem…Rich is a fuel mixture problem…Clean your throttle body and air-flow sensor…Run a bottle of Chevron Techron injector cleaner through it. Or step all the way up to BG Formula 44K…Good Luck…

P0171 is lean bank 1, P0175 is rich bank 2. Strange that you would have lean on one side and rich on the other.

A big vacuum leak perhaps…Or a plugged injector…

Did you do the timing cover and coil at the same time? If you did retrace your steps and look for vacuum leaks, connectors that could have been swapped or vacuum lines that could have been incorrectly connected. Most times when a code occurs just after a repair it is something related to the repair.

“P0171 is lean bank 1, P0175 is rich bank 2. Strange that you would have lean on one side and rich on the other.”

I've heard that if you cross-connect the 02 sensors, the ECU will runaway rich and/or lean: the "bank 1" O2 will read rich, and the ECU will correct the wrong bank, causing lean on "bank 2" O2...causing the ECU to enrich the other bank, and so on...

Did you recently have exhaust/emission work done?

Might be wrong on 0171. Maybe it was 0172. I looked up both online and found bank 1-2 rich condition. I clear code, and drive 30 miles, no cel. Code seems to pop up at first start. I will check it out

If both banks rich on startup, I would try Caddyman’s suggestion to clean MAF.

with all these misfires you may have a clogged up cat especially if it only seems to happen at higher rpm. it was easy enough for me to pull the exhaust off the header on the 03 monte carlo i was working on and it cleared the problem up. the way i seen it was it was a free test i can do. but i do think this is more of a high rpm power robber the car i was working on ran fine at idle.