Why do I get the feeling you are about to overwhelm me with data?

Here'* a link to the data collected so far - it'* in the form of graphs saved to a Word document.

https://docs.google.com/file/d/0Bwdz...it?usp=sharing

This data was collected with the logger set to 'normal' or 'road test' mode which shows the pattern of open loop to closed loop and then back to open loop behaviour that I've been describing. The closed loop period starts at around 6 minutes and then goes back to open loop at around the 15-16 minute mark.

The short term and long term trim values appear to be compensating for a rich condition which surprises me because that doesn't fit with my vacuum leak theory which would make conditions go lean.

Check out the large number of idle flags being set and not just during idle conditions. I'm not 100% sure about this but I'm thinking that an idle flag will be set as a result of an unacceptable variation in RPM. It may also set for an unacceptable variation in RPM at a constant TPS which may explain the large number of hits over a wide range of driving conditions. In any case, as I've mentioned before, there is a noticeable roughness in the idle but not to the point that it'* threatening to stall - it'* just noticeable enough to be annoying.

Also surprising to me is that the TCC doesn't operate in open loop. I've always know that it doesn't activate until warmed up but I didn't realize that it was tied directly to the open loop requirement.

Going back to the idle data, there are some good examples of the idle RPM variations at both the 8 minute mark (in closed loop) and the 20 minute mark (in closed loop). It might be worthwhile to expand the O2 and INT data during those periods to see if anything obvious stands out. If you're interested in playing with the ranging of the data let me know and I'll set up a link to the data file.

I've also now collected data for a similar run but with the logger set to 'field test' mode. In this mode, the ECM stays in closed loop for the entire period after warm up so it should be interesting to compare with the 'normal' run data. I'll have this data ready shortly.

In any case, the information acquired using the data logger in conjunction with Jonas Bylund'* Winaldl provides so much more detail than the scanner tool that I doubt the scanner will get much use in the future unless Winaldl doesn't have a definiton files for one of my OBD1 GMs.

Actually, is it normal for the IAC valve to be bouncing around like it'* doing between idling sessions? The only time it'* relatively stable is when the engine is idling, otherwise it'* constantly bouncing around from about 40 steps to 100 steps. In fact, for the first 8 minutes or so it'* bouncing from about 70 to 120 steps and then changes to 40 to 100 for the rest of the test drive. I'm not sure what'* normal for this but it doesn't seem to make sense to me that it should be making adjustments when the engine isn't idling. Any thoughts on that question?

Here'* a link to the 'field mode' run data if anyone'* interested.

https://docs.google.com/file/d/0Bwdz...it?usp=sharing

In this case the ECM stays closed loop after the warm up period for the rest of the test run. The BLM once again is showing an overall rich condition for the entire test run.

In any case, I decided to look for vacuum leaks so I took apart all of the vacuum lines and inspected the hoses, changed what looked suspicious and put some extra clamps on. I also took apart the fuel rail and cleaned up around the ports, changed the injector O-rings and put it back together again. I also took out the plugs for inspection and they're all the same - very clean, if anything it looks somewhat lean.

plug.jpg

The car now runs without any rough idle so there obviously was a vacuum leak - the hose to the PCV valve was suspiciously loose so I'm guessing that was the cause. However, it still goes open loop after 10 minutes in normal mode - just like clockwork. I'm beginning to wonder if maybe there was a change up on the chip that wasn't followed up on this car (I'm the 3rd owner). It may have been running like this since day one without anyone knowing otherwise as there are no codes being set to flag a problem. So, guess I'll follow up with GM to see if they still have the records this far back.

One other thing I noticed is that the AC has been removed and the connectors just tied off. I know the ECM is expecting a signal from the AC so maybe I need to look into this as the problem - I know it'* a stretch but there'* nothing else to look at that I can think of. Another option is to operate the car in field mode so that it stays in closed loop but I'd rather not do that yet.

Also time to log another set of data to see if I'm still getting all of those idle flags.

hmmm - I tried to paste a photo of the plug but not sure if it worked - or is there some other way to do this??

paste dont work, you have to either have it on like photobucket, or do advanced then upload it to the site

thanks Justin - I'll try Google drive here'* the photo of the plug:

ok - once again - here'* the image from photobucket:

[IMG][/IMG]

like you said, plug looks pretty lean.

I just came across this RPO code for this 87 Buick:
NM5 EMISSION SYSTEM, NON-CLOSED LOOP (CANADA)
Does this mean what I think it means?
In other words, is this vehicle designed to operate without closed loop feedback? If so, why does it have an O2 sensor and why does it go closed loop for a fixed 10 minute period every run cycle?
Anyone come across this before?