I have been on a diagnostic kick for a couple weeks. For backstory of what started this you can refer to this post: https://www.ford-trucks.com/forums/s...0&goto=newpost

My scanner has an option for live operating data. It was showing that my Bank 1 Sensor 1 voltage was bouncing from .01 - .8 Volts within seconds of each other. It did not matter what the load or throttle was at. The Bank 1 Sensor 2 voltage was always steady and seemed to change appropriately based on load and throttle response. Cruising @ 65 mph in 5th gear Sensor 2 Bank 1 was about .2 - .3 volts. The Bank 2 Sensor 1 (sensor in the rear of the cat) was also bouncing from .2 to .85 Volts. I decided that 2 of my 3 02 sensors were probably bad. Before I started it I disconected the battery to clear the ECU memory. I changed all three O2 sensors, hooked it all back up and the voltage is still doing the same thing. It did seem to run better and my lag from idle seem to be gone but the bouncing voltage on 2 of the three sensors still remains.

Is my issue, a bad wiring harness, ecu not interpretting the Sensor data correctly, Catalytic worn out, bad injectors on one side of the engine - I just am not sure? If someone with extensive Engine Management experience could chime in I would really appreciate it.

 

The mixture is supposed to switch from lean to rich because that helps the catalytic converter to function better.

 

OK here's the deal, 2 of your sensors are working exactly as they should.. switching rapidly from low to high voltage. I also think that your two main(front) sensors are bank 1 sensor 1 and bank 2 sensor 1. The one behind the cat should be bank 1 sensor 2 and I don't know if it's supposed to act differently or not, could be since it's function is different.

 

Is it supposed to switch that much in voltage under normal driving conditions? If this is true then my one sensor that is not fluctuating much - is it defective or another underlining issue? This whole thing has stemmed from having a lack of power, spark knock under load, and a hesitation or lag coming off of idle.

 

The sensor that is not switching is the after-cat sensor, which basically reads a constant rich mixture if the catalyst is working properly (lack of oxygen). I think the sensors are all acting normally. I didn't catch on to this until Paul (Conaski) mentioned the bank and sensor numbers and I went back and re-read the first post.

 

Isn't the Bank 1 sensors all pre-cat, and Bank 2 sensor(s) are post or after cat? My scanner shows two Bank 1 sensors and only one Bank 2 sensor. I always thought Bank 2 was post cat.

 

No.. bank 1 is passenger side, bank 2 is drivers side, this goes all the way back to the 5.0HO, the first motor with dual sensors.

 

The sensor after the converter (furthest to the rear of the truck) signal should remain steady when the O2 and converter has warmed up. When this sensor starts switching like the 2 sensors before the converter do it usually means the converter material has failed (or is missing for those who like to gut them) and the computer normally turns on a P0420 which is a catalyst efficiency code because the computer is not seeing a steady signal like it should on that particular sensor.

 

Thanks for clearing that up. I checked my other cars and my '03 Maxima fluctuates the same, but my Honda Odyssey dosen't flucuate hardly at all. On the Honda the Precat and Postcat stay consitant and only flucutuates .05 Volts +/-. Very strange the differences.

The Ford at idle is showing that my TPS is @ 18% when the other two cars at idle are showing 0% on the TPS. Is this normal for a Ford?

On the fuel trim percentages the short term fuel is trying to stay close to 0%, while the long term is bouncing all over the place +/-. If running properly what should I be noticing on the fuel short and long term % rates?

Is it normal to show at idle that it is running 42% load? My Nissan at idle shows a 18% load, and the Honda showed a 25% load.

I don't know if changing these 02's have completely fixed my problem. It does seem to run much better but I won't know for sure until I hook up to a load and go for a spin. Thanks for the input - it has been very helpful!

 

On my truck TPS of 18% corresponds to 0.9v which is the closed position and that's good. However engine load should be in the 20% range at idle, what is your MAF meter reading? It should be around 1v at idle. And short term fuel trim is the one that should be bouncing all over the place, long term is only updated if the short term shows a repeated tendancy in a particular direction.

 

My Scanner does not show MAF voltage but it does show intake @ 1.18 lbs/min. This reading was at idle with 42% load. I will have to take a manual reading on the MAF. Do I take that reading on pin 4 (T/LB) or pin 5 (LB/R)? Alldata has a table that shows what the voltage for the MAF should be at gm / sec (? grams per sec). The lowest voltage signal the table shows is .34v which for a 7.5L is supposed to be reading 1.35 gm/sec. So now I need to figure out how to convert gm/sec to lbs/hr and also which pin to measure that on. Thanks Paul

 

My tuner software also displays the MAF in Kg/hr and an output of 1v equates to about 31kg/hr and that converts to about 1.15 lbs/min so I'd say your MAF meter is OK. According to this document.. EEC IV Inner Workings

"The formula for Load is basically the amount of incoming air ratioed against how much one cylinder can hold at standard pressure/density".

So obviously atmospheric pressure is important to this calculation. I'm not sure if your truck has a Baro sensor but that would be the next thing to look at because your engine is showing an artifically high load at idle and the computer will be retarding the igition to compensate and that will result in a loss of power.

 

Are you refering to a MAP sensor? I don't think my truck is using that, I think only the speed density (federal) trucks are using that - but I will double check.

 

Yes SD motors have a MAP sensor, but some MAF motors use the same sensor to measure atmospheric pressure, it's just vented to air instead of being connected to the intake.. that's how my truck is setup. You'll have to look to see if there is one on the passenger fender or back on the firewall.

 

I don't have a MAP sensor. Unless another sensor is doing the job. I referenced my Ford technical service DVD and with my Calibration code: (6-97Q-R06) and Ford is not showing I have that sensor as part of my parts list: Here is what my Calibration list includes:

SENSOR ASSY., (Catalyst Exhaust Gas Oxygen Monitor- 15' Pigtail - DOWNSTREAM) F65F 9G444-BA F65Z 9G444-B
SENSOR ASSY., (Catalyst Exhaust Gas Oxygen Monitor- 19' Pigtail - DOWNSTREAM) F65F 9G444-CA F65Z 9G444-C
RESERVIOR ASSY., (EGR Vacuum) FOTE 9E453-AA FOTZ 9E453-A
CONTROL ASSY., (EGR Vacuum Regulator) FOTE 9J459-A1A FOTZ 9J459-A
SENSOR ASSY., (EGR Pressure Valve) F48E 9J460-BA, BB F4ZZ 9J460-B
SENSOR ASSY., (Exhaust Gas Oxygen - UPSTREAM) F68F 9F472-AA,BA,CA F68Z 9F472-A,B,C
VALVE ASSY., (EGR) F6TE 9D475-C2A, C4A F6TZ 9D475-C
TUBE ASSY., (EGR Valve to Exhaust Manifold) F6TE 9D477-NB F6TZ 9D477-N
INJECTOR ASSY., (Fuel) F1TE 9F593-D1A F1TZ 9F593-C
VALVE ASSY., (Throttle Air By-Pass) F2LE 9F715-AD, A1D F2LY 9F715-A
REGULATOR ASSY., (Fuel Charging Pressure) F4SE 9C968-AA F4SZ 9C968-A
POTENTIOMETER ASSY., (Throttle Position Sensor) F4SF 9B989-AA F4SZ 9B989-A
DISTRIBUTOR ASSY.) F5TE 12127-BA F5TZ 12127-B
SENSOR ASSY., (Mass Airflow) F5OF 12B579-AA F5OY 12B579-A
SENSOR ASSY., (Engine Electronic Control Coolant Temperature) F5AF 12A648-AA F5AZ 12A648-A
PROCESSOR AND CALIBRATOR ASSY., (Powertrain Control Module - EEC-V - TYPE: ML1-442 - REPROGRAMMABLE) F6TF 12A650-AGC F6TZ 12A650-AGC
SENSOR ASSY., (Air Charge Temperature) F5AF 12A697-AA F5AZ 12A697-A

My scanner did not show any MAP data either. I referenced AllData and it shows a MAP but it has a foot note for Federal Emissions only. Any other thoughts or ideas?