cardinexile

98 Scab XL 4.6 (romeo) 4X4 250K miles. I've been working on this for a year- truck was running great with a bit of a miss. Last week, All of a sudden, the truck had no power. could barely get up to 30 mph. I have changed the fuel pump, thinking that was the problem, since I had already changed the Fuel Filter, IAC, TPS, EGR, PTFE, plugs (motorcraft), wires and coils and both B@ O2 sensors and have less than 500 miles on the truck since I got it. Also have changed out the vacuum lines that were dry rotted.
Was throwing P0171/4, Evap, Bank 2S2 and random misfire codes. I then thought, since the truck was running like it was constipated, that the Cats were clogged so I had them cut off and straight pipe welded in. The upstream bank 2 cat was in pieces and the downstream cat was clogged with them. The only code I am getting currently is P0174- Bank 2 lean condition. I have previously done a compression test, getting between 80 and 120, which I know is low, but trying to make the engine last until I can build another and install it if needed.
Trouble shooting steps: Code reader, live data looks like it may have a bad O2 @ B1S1. Intermittent 0.00 readings while all the others cycle normally.
Pulled all the plug wires and checked for spark. Same with injectors. Only half of the cylinders made a difference in the running. Cyl 1, 2, 3 and 7 do not make the engine run worse. the others do. Listened to all the injectors and they seem to be working. Checked the inertial switch and it is fine. I've got spark and the misfires-even they don't show as a code are not isolated to one coil. Will run another fuel pressure check tomorrow to eliminate that as a possible cause. I removed and cleaned the throttle body this week and it made no difference.


AAARGH! I'm at my wit's end , please give me something else to look at- Maybe the PCM? the Fuel Pressure Regulator? WTFIWWTT?

Mod (Ret.)

The cylinders that are low in compression could be the culprits; the PCM mapping can only go so far to adjust the fuel pressure mixture based on input from the O2's, the MAF, and throttle position. The low compression cylinders may be dumping oil being bypassed to the exhaust, and causing the O2's to provide an off scale reading.

Neptunescab

Sounds like what happened to my moms old expedition it ended up being that one of the timing chain guides broke and it threw off timing and ended up killing the motor cause these are interference motors but didnt set off any codes for some reason