1998 F150. Has a miss. Runs good when it gets up to 40mph. Showing codes po171 & po174. So far have replaced intake gaskets & cleaned mass air flow sensor. Still missing & still showing codes.

Need some expertise please......Now what????

 

Pulled each injector plug off and best I can tell is that #4 and #8 are not firing. What we have done so far is:
1. Intake Gaskets
2. Clean MAF
3. New Plugs
4. New Wires
5. New Fuel Filter
6. New PCV Hose
7. Seafoam and 92 Octane Gas - been thru about 1/2 tank so far

My next thought is to swap out injectors from 2 and 6 to see if it's an injector issue? After that...I'm outta ideas!????

 

I sure you did this, but check real close for any vacuum leaks

 

I was told by a mechanic friend I needed to put new o2 sensors in...after readinf what you have done, what led you to replace the items you did replace?

 

I suppose I should mention I am new here

 

I've had those codes and found it was a hose in the air intake leaking. Those codes are both banks running lean and the ECM couldn't add enuff fuel to compensate. So it was a vacuum leak only.

 

I'm chasing the same problem. Next step is to get a reading on fuel pressure. Low would throw lean codes for both banks (071 and 074). Kaboom, where in the intake did you find your leak? Carb cleaner idle test is not revealing anything, and I don't have the low idle sputter that many report.

 

a severe misfire can cause lean codes, during a misfire the fuel goes unburned but the oxygen is not consumed either, and since oxygen sensors react to O2 in the exhuast, it can read lean, if would suspect that your coil pack is shorted causing the misfires, and since you engine is set up for companioin firing cylinders, a bad coil can effect cylinders on opposite banks causing both to read leak, also, if you have access to a scan tool that will read data, see what the baro reading is, is approx 160HZ at sea level and that read gets lower as altitude increases, dallas is approx 750 ft above sea level and an average reading is 157 HZ, if it reads too low, will cause lean conditions, Good Luck

 

My leak was at the connection before the MAF. The PCV line behind the adapter for the inlet is hidden and goes bad. You say you have tried carb cleaner so that leads me to believe you may have a clogged fuel filter or bad fuel pump. Low fuel delivery causes a lean condition.