Yes the fuel system going open loop again says that most likely the computer does not like one or more sensor inputs. O2 sensors are a possibility. The only meaningful look at O2 sensors is live data graphing, can you do this? Another possibility is the O2 sensor heaters but usually you will get a code, unless its intermittent. The fuel trims do get worse at 2500 but not as bad as the freeze frame data which implies an intermittent issue or an issue under a load. Also your coolant temp is too low or the reading is anyhow, if the truck was warmed up. What id the ECT value when driving? So I would:

1. Graph O2 sensors especially when the system glitches to OL
2. Check ECT value warmed up and driving
3. Check fuel trims at a steady state 2500 while driving
4. Look for exhaust and vacuum leaks
5. Look at fuel pressure at 2500 rpm maybe even driving to see if its high (regulator/return line)

Intermittent electrical failures will test you sometimes, they can be hard to catch and diagnose. Another cause for a dropout can be wiring continuity or a glitch is reference voltages (5/12v). It might be worth getting a voltmeter on the reference voltage buses and see if they drop out during an event although I realize that this can be like trying to catch a lighting strike with a camera.

George

 

My Inova 3160 will not graph o2 sensor data, but it has a mode where it tests upstream sensor switch times. Would this data help you estimate their condition?

I know a retired shop owner who has an older Snapon tester, would you know if they have a graphing function? I know nothing about them.

As for driving ECTs this time of year they run in the 175 range; during summer with ac they run up at 190s. But I will check on my next trip into town, along with fuel trim at about 2000 rpm’s, as 2500 will put me over speed limit significantly, and it will have to be 4th gear, not 5th.

I think I have some fairly recent fuel pressure data which might show 2.5K rpm pressures, I’ll look. If not will no load data work?

I looked at you tube for a smoke machine, some guy built one out of pvc pipe that might not be too difficult to do. So I’ll give it a try to find vacuum leaks.

vic

 

I am not familiar with that function on the Innova. Switching times are important and so if it correctly measures rise and fall times then that helps to rule out a sluggish sensor but I don;t know if it also looks for a healthy switching frequency which is alo important.

Some Snap ons graph and some do not, depends on the model.

A stubbornly low reported engine temp will cause a rich fuel mixture. So will high fuel pressures (regulator or return line) as well as leaking injectors.

George