Chicken or the egg? lean cause of trim or O2?

[budwich]

Recently, I got an elm327 box because we had a laptop "lying around". It seems to work fine with the freeware stuff that is on the net but while playing with it, I noticed that the long term trim on the driver's side was significant (rich) while on the passenger's side was "neutral" (ie. zero). Then I was watching the O2 sensors. They were both switching BUT the driver's sides was "switching" from 0 to some value (high) indicating "lean" while the passenger side was "switching / cycling" from + / - values around 0 (ie. cycling lean / rich). My question is the "one sided switching" of the O2 sensor the cause of the "high rich" trim value or is the "rich" trim value the cause of the "one sided" O2 sensor sensing? ....

There are no codes. Idle is around 750 -> 800 once warm up has occurred. The "free ware" doesn't give fuel pressure or manifold pressure readings ... which is too bad but still is a lot more info than I was expecting for such a "cheap" setup.

Thanks for any coments / suggestions.

 

[96eb96]

Recently, I got an elm327 box because we had a laptop "lying around". It seems to work fine with the freeware stuff that is on the net but while playing with it, I noticed that the long term trim on the driver's side was significant (rich) while on the passenger's side was "neutral" (ie. zero). Then I was watching the O2 sensors. They were both switching BUT the driver's sides was "switching" from 0 to some value (high) indicating "lean" while the passenger side was "switching / cycling" from + / - values around 0 (ie. cycling lean / rich). My question is the "one sided switching" of the O2 sensor the cause of the "high rich" trim value or is the "rich" trim value the cause of the "one sided" O2 sensor sensing? ....

There are no codes. Idle is around 750 -> 800 once warm up has occurred. The "free ware" doesn't give fuel pressure or manifold pressure readings ... which is too bad but still is a lot more info than I was expecting for such a "cheap" setup.

Thanks for any coments / suggestions.

Are there any other symptoms?

Does this pattern change after warmup?

 

[manaen]

How many o2 sensors do you have on your truck? is it possible your reading from a sensor located behind the CAT.

which engine do you have?

 

[budwich]

Its a 4.0 OHV.... its bank2 sensor 1 which is the driver's side ... right? Prior to warm up, it idles a little high which I kind of expect.... I wasn't watching "everything" at once cause you can only display / see what their screens have been setup for. For instance, I didn't watch for a "switch" from "open loop" to "close loop" operation but do know that it was in closed loop when I was looking at the trim and O2. This was about 4-5 mins into driving and things were "well warm" by then. I am going to do some more "testing" when I can get an "extra" set of hands or eyes to either drive or watch..... not sure how the "cell phone crowd" are able to "text" and drive but it is tough even when you are looking at a 15" display...

 

[manaen]

do you have any drivability issues?

Maybe try switching the O2 sensors from side to side, then re-run the test to see if it follows the sensor.

If it stays on the same bank you eliminated the o2 and you can move onto the next level.

The 96 OHV I believe has a shared intake so any vacuum hose leaks will cause lean on both banks, so it would have to be a clogged fuel injector or leak around a seal below the upper section of the intake. Read you plugs and see if any or all of the cylinders on that side are running lean.

 

[budwich]

I went on a "test run" at noon (30C outside)... 15 km or so... free traffic speed. Everything look like it should bank1 and 2 O2's oscillating in opposite step with trims (rich and lean) with long term trim running basically slightly lean. Not sure why the other day the bank 2 was running rich but maybe different driving conditions. The first time, the vehicle was used during the day for a 100 km road trip and then "rested" prior to testing and the second time, it sat over night with no use. Maybe its normal but since I just got the tool / software, I don't know what to expect. I guess I need a few more runs.

As for the "do you have driveability issues"... sometimes it has high idle (2k) as you come to a stop but I haven't been able to determine when this might happen and have not had the "live data" monitor going when it happens.

 

[manaen]

you may have an intermittent vacuum leak which would explain the high idle and o2 readings, just something to keep in mind. I would also check the IAC just to make sure it is not getting stuck in the open position from time to time.

 

[NHale623]

The "free ware" doesn't give fuel pressure or manifold pressure readings ... which is too bad but still is a lot more info than I was expecting for such a "cheap" setup.

It has nothing to do with the freeware. Your truck doesn't have sensors to monitor fuel pressure or manifold pressure.

 

[budwich]

Thanks... I kind of figured that after looking at stuff in the truck CD. As a GM man, I thought that manifold pressure would be monitored some way as in GMland they do. It would appear that a vacuum leak is my most likely candidate for the "unexpected" high idle. It seems when it occurs, during braking that if I release and reapply the brake, the high idle drops immediately which may indicate a leak in the booster but when I tested "as per CD", it appears to act normal. Anyways, I have the gaskets for the intake, just need the time and courage to tackle the job. I have done the "spray carb cleaner" with no indication of a problem but with 240Kkm, it can't hurt to replace the gaskets... there has been signs of coolant leaks in the past.