Ok, 89 F150, 5.0, 5 speed, 4wd.
96 Explorer roller cam, shorty headers, rear cat removed, K&N air filter.
New plugs, wires, cap, rotor, TFI, PIP, TPS, O2, EGR solenoid, coil, MAP sensor, and fuel pressure regulator. No vacuum leaks to be found.
Issue is I get 12 mpg, no matter how gingerly I use the gas pedal. Since I've had it, the one code that is always there, engine running and engine off in the ECU memory, is 41, which is System Indicates Lean/No HO2S Switching Detected. What could cause this? The new O2 sensor is in the factory location, the little H-pipe before the cats. Is there some known nuance that could cause this code and result in the ECU over compensating and ruining my mileage?
I also get code 29, Insufficient Input From Vehicle Speed Sensor, sometimes with KOEO test. What is the significance of that?
Thanks!

 

You may want to follow the wiring from where the o2 sensor plugs into the first connector. I had a similar issue and turned out there was a connector unplugged behind the battery which was preventing the o2 from switching, plugged it back in and no more codes. Also check for any damaged wiring. It would help to go through and clean up the connectors (quick drying electronic clean) as well as any body grounds (emery cloth or wire wheel, both frame and eyelet) that you can find and sparingly apply some dielectric grease to both grounds and connectors to help prevent future problems. Problems like this can take a while to track down and usually end up being something easily fixed with a little patience and a common sense approach.

Same goes for the VSS, cleaning up connectors and grounds as well as checking the wiring.

 

I did think I should check the wiring for the O2. Do you know off hand what ECU pins the O2 feeds? I figured shorting the pins at the O2 plug and testing continuity at the ECU pins would be the quickest way to determine there's a break. If it fails that, then I can dive deeper...
And what is VSS?

 

No I don't know, it shouldn't be that hard to find somewhere online or from someone with a Haynes/Chilton.

Vehicle Speed Sensor

 

Well finally got around to checking the wiring...
O2 sensor signal was not getting to pin 49, which several diagrams say is the HEGO pin.
So I traced it and found the O2 signal was going to a four prong plug over by the ECU (O2 wire was the only wire going to it though). This plug was not connected to anything and there are no plugs in sight to connect it to. So I traced the pin 49 orange wire from the ECU and found it went to the engine harness with the injectors and such. That orange wire was outside the harness at the back of the manifold, by itself, with a ring terminal someone put on it and was bolted to the valve cover.
So I thought that would explain the lean code. I spliced the O2 wire to this orange wire, drove a bit, and still have code 41... Any ideas now?!...
On a lighter note, I found the plug for the speed sensor was all broken. I seated the pins for now and that code is gone...
Thanks for any and all help!

 

Can anyone confirm pin 49 is correct for the O2 input?

 

Diagrams online were wrong...
The wire behind the manifold was supposed to be grounded. It's the HEGO ground for the ECU. Corrected that and no more 41 and gas mileage even went up.
Now just 44 running, and 33 not running.
What does Secondary Air System Inoperative mean? Is that the air pump?

 

33 is for the EGR not opening or not opening fast enough, could be a small vacuum leak or bad diaphragm in the EGR.

44 is indicative of several possible problems. Blocked vacuum lines, defective air pump, diverter valve, or TAB and/or TAD solenoid. If the vacuum lines and smog pump check out, check for 12VDC (battery voltage) at each terminal on each solenoid (Total of four terminals; two per solenoid). The solenoids should be located near the ignition coil on the driver's side of the intake manifold. In order to do this you will have to run the KOEO test and put the throttle to the floor AFTER the last code is generated. At that time both solenoids should each have 12VDC at one terminal and zero voltage at the other terminal. If they do, put the throttle to the floor again. Now BOTH terminals on BOTH solenoids should have 12VDC. If the solenoids don't pass this test completely, the problem is electrical (wiring) or a failed solenoid.

 

Thanks, that solenoid test is helpful.
The EGR position sensor checked out fine, the diaphragm holds vacuum and moves, and the solenoid is new. Does it actually test the EGR during the test, or is it just a memory code from when it's running? I don't get the code while engine running, so wondering if that means the canister leaks down when the engine is off and that's why it doesn't see the EGR open then...?

 

Start the KOEO test and pull the jumper while it's starting the test to clear the codes, it may just be an old code from before replacing the solenoid, and that code could also be from it just not opening fast enough (cold weather, momentary loss of vacuum, etc...) at some point in time.