Hey guys.

Got a 94 f150. Just did an h.o. swap and built true duals with long tube headers, magna flow high flow cats, and flowmaster 44s. Originally messed up and put o2 sensor in a cross over back further than it should be. Eliminated crossover and put o2 sensor in the tail of the passenger side header. Truck runs good but is really sucking the fuel. Problem I'm having is o2 sensor is stuck at .05. it should be switching between 0-1. My short term fuel trim is stuck at 0. My long term is stuck at -56. Got a 172 code. O2 sensor senses lean. Damn near all the sensors are new. 02 is not but I have went through 3. Mone and the 2 off the doner car. All 3 are the same sensor. It also will not go into closed loop. It's staying stuck on open loop. A guy told me I'm going to have to chip it. Any advice would sure be appreciated. I'm at my wit's end here. Been trying to figure this thing out for 2 months now.

 

Gonna have to fix that O2 sensor issue. Heated sensor? Heater circuit working?

 

I did check all of that and it seems the heater circuit is working fine. The resistance values and voltage values are within specs.

 

What did you change electrically with the HO swap?

 

Nothing. Just used block and heads. Everything else is off my other motor or replaced new.

 

So you didn't change the injector wiring in any way and just routed the spark plugs wires to the HO firing order? And it's still using the truck PCM?

 

Sorry about late reply. All the injector wiring is the same. I rebuilt my original injectors, including new pintles except for two I had to replace. New. Not reman. I took the other posters advice and installed a new o2 sensor. That really did help so thank you. Truck runs much better now. Got rid of the 172 code. O2 sensor switches like it should. Short term fuel trim fluctuates like it should. Problem now is that I still get an idle fluctuation at stop. It will sometimes die on me when coming to a stop. Long term fuel trim is still stuck at -56. It stutters when getting up to speed when I'm not giving it much throttle but will run like a scared rabbit when I get down on it. I'm now getting a 173 code, o2 sensor senses rich. That would explain why my long term fuel trim is so negative because the computer is trying to lean it back out. I'm getting too much fuel for some reason. Checked injectors and they wasn't leaking. Fuel pressure is perfect. 40 psi on cranking and 32 at idle. Give it gas and it climbs 4 psi and then drops back to 32. Vacuum holding at 20 hg. Drops to about 14 when giving gas which it should then goes back up to 20. It's showing none of the classic symptoms of a bad fuel pressure regulator. No fuel in vacuum, oil, or out exhaust. Pop vacuum line off while it's running and no fuel comes out. No hard start. Im at my wit's end here trying to figure this thing out. I'm making progress but have hit a brick wall. Anybody who knows about fuel trim and what to do here I would really appreciate the help.

 

And yeah. Wired up for h.o. firing order which is 351 firing order and is still using the truck pcm. I couldn't use the one from the t- bird because it is set for 2 upstream o2 sensors and is also set up for a maf where mine has a map and 1 o2 sensor.