Hello, i have a 98 f150 with a 4.2. the check engine light is set. when scanned I retrieve po304, 305, 306 and po175. i have done the quick remedies like clean the maf have checked for and even fixed aminor vacuum leak but have not suceeded in removing any code. ive noticed most suggestions dont reflect that the rich condition affects only one bank (2) of the engine. the fuel trim numbers for bank 2 are stft -10.9 ltft -0.7. note that these value setat 1580 rpm and 8mph. i have seem them much more negative like -12 and -25.5. im going to collect some real time values with the help of a friend today. any thoughts or advice would be very appriciated. thank you.
Also, Ive never posted to a forum before so i apologize for any errors of protocol.

 

Have you fixed the misfires? Those are on the same bank as the rich code. How many miles on the spark plugs and plug wires?

 

I replaced the plugs but not the wires. I also changed the coil pack as I had one and the o2 sensors on that bank.

 

Have you cleared the codes to see if they come back?

 

yes, I have and they do come back. Earlier today I erased the codes and they returned. In the freeze frame the trim values were : stft b1 4.6, ltft b1:14.8, stft b2::-16.4, ltft b2: -0.7. its difficult to theorize a rich condition that affects only one bank of cylinders since it uses port injection.is it plausable that one injector leaking fuel would cause the other two cylinders on that bank to misfire?

 

Do you have an exhaust leak on that side before the upstream sensor? You may have an intake leak if you can't find a vacuum leak anywhere else.

 

No, I dont have an exhaust leak. i replaced the thermostat because the heat gauge was barely into the operating range.Although the old one was not stuck open, the gauge moves farther up the scale than before.. The new stst was a 195 deg unit. hooked up to my obd2 scanner, after idling for 25 minutes, the water temp maxxed out at 188 degrees. however, the po175 code has not reset and I only get codes po304 and po306. Iam going to install new plug wires and a new temp sender after work today.The fuel trim numbers arestft b1: 0, ltft b1: 10.1, stft b2:-3.1, ltft b2:10.1. this with coolant temp of 188. will post further results tonight.