Thread: 97 P38 Oxygen Sensor issue?

O2 sensor tests
Thanks to everyone with advise on how to test these. A few mechanic's have already done this and advise they are fine, however, the power loss is intermittent (lasting 1 1/2 mins usually) so I'd need to be testing them while it's happening. Not practical without live software running?

iPhone OBDII data capture
Not sure if i'm more or less confused after capturing some data of the intermittent power loss recently.

Check out the graph attached. I captured this using my iPhone and the Rev OBDII app DevToaster - Rev - iPhone app development, Great iPhone apps, and more. The app is as limited as one would expect, with some of the values not working at all (a general P38 issue?) the stand out value to me is the "Fuel Trim Short Bank 1" value that is possibly changing more than it should (?).

Before I go any further, I have to advise that I'm still trying to work out what the "Fuel Trim Short Bank 1" is... After a little research I gather that it's something to do with the ECU's ability to change mixture based on values coming from sensors. I'm guessing that the O2 sensors play a big part in this and may be a cause of errant values. However, i'm not sure what correct values look like, so this may all be me on a wild goose chase, not knowing what a goose even is!

Anyway, the graph is pretty with lines going up and down and looks like the how the engine feels during the intermittent power losses. I've multiplied some of the values to have them in line with each other for easier comparison.

Next
- Can anyone recommend good PC software to capture live engine data? Capturing actual O2 sensor data might be helpful.
- Anyone see anything there that points to anything?

Thanks all,

Dave

What limited experience I have says a "short term fuel trim" under 5% is fine, according to my scanner on newer vehicles than yours.

I use the android app called Torque, which talks to a bluetooth ODBII adaptor. It logs data. The adaptor I have is crappola, and often refuses to connect to the phone.

iPhone FTW

I would think that the graph doesn't tell much about the O2 sensors as the sampling time is 2 seconds, and O2 sensors should react several times a second.
Having said that the fuel trim appears to average around zero which one would expect on a motor with MAF and other sensors in good condition, as this should be around lambda.
So it appears to me that the sensors are doing something , but whether they are slow or not cannot be seen. AFAIK sensors usually become slower as they age.

Regards Philip A