FORScan forum

I'm a newbie at using a scan tool, so feel free to assume I know nothing My vehicle is a 2003 ford e350 with 5.4l triton running on dedicated cng. It's running rough at idle and in the speed range of 35-50 mph. The rough running consists of engine vibration and low power...I can put the throttle to the floor and it won't accelerate for a while, then after between 15-60 seconds, it kicks in and runs normally. When it first started happening, I had a P1131 (bank 1 lean, o2 sensor error), so I replaced the o2 sensor for bank 1 and it ran marginally better. I reset the CEL, and the next time it came on, I had P1151 (bank 2 lean, o2 sensor error). The bank 2 sensor is fairly new and seems to be functioning like the bank 1 sensor when I look at the voltages in FORScan.

So, running FORScan, the only obvious errors are fuelsys01 CL-fault and fuelsys 02 error. If I'm understanding this correctly, this means bank 1 is running in closed loop but is using some alternative parameters to determine fuel trims because of a fault somewhere else in the loop. Since fuelsys 02 just reads "error", what is a typical cause for this message, and is this likely why bank 1 is showing a fault?

Things I've done that had little to no effect on the running of the engine: cleaned MAF sensor, new air filter, new o2 sensors, flushed fuel system. My suspicion is that it's a fuel injector, spark plug, or spark coil. I know I can try things like swapping injectors or coils around, but working on a van engine is not my idea of fun. I would really like to get more information from the scanner before I do anymore brute-force diagnosis.


Thanks for this software and for any additional tips anyone might offer! bill

billnunez wrote:So, running FORScan, the only obvious errors are fuelsys01 CL-fault and fuelsys 02 error. If I'm understanding this correctly, this means bank 1 is running in closed loop but is using some alternative parameters to determine fuel trims because of a fault somewhere else in the loop. Since fuelsys 02 just reads "error", what is a typical cause for this message, and is this likely why bank 1 is showing a fault?

The FUELSYS2 Error means FORScan is unable to interprete the PID value returned by ECU (it is confusing, we know, probably needed more clear indication to distinguish such type of errors). Most likely, because the FUELSYS2 PID is not supported on this engine. Even in case of 2 banks (V6/V8 engines), Ford ECUs have a single fuel system to manage both of them (at least, all the Ford engines we touched during this project do so). So the FUELSYS1 manages both bank and CL-Fault most likely means that the loop is closed, but only using a signal from the bank1 oxygen sensor. Oxygen sensor from the bank2 seems not used because for some reason ECU considers it faulty (P1151 you mentioned above).

So, the most weird thing here is that you checked the signal from the sensor bank 2 and it seems to be ok. In contrast to P0171/P0174 error codes, that also mean lean conditions but may be caused by different reasons, P1131/P1151 are mainly related to the O2 sensors itself. So, according to the information you provided, either O2 sensor or it is connection is dead. Please note the O2 sensor bank 2 should not reporoduce the signal from bank1 exactly - they are independent.

So, we recommend you to double check the signal from the bank2 sensor once again. Please note sensors' ordering may look confusing, so: please note that number 11 in the PID acronym means Oxygen sensor 1 bank 1 (upstream), number 21 means Oxygen sensor 2 bank 1 (downstream - usually after catalyst), 21 means oxygen sensor 1 bank 2 etc. So you need to find a PID O2S21 or similar and check its voltage and how it changes.