I'm not sure of anything anymore. That screen shot was with the car at idle. I've seen the same type of data for the ST trims at idle with my corded scanner. I am going to follow up on the IAC as I really think it is involved with the problem in some way. If its internal plunger is stuttering or opening and closing quickly, it cold account for fuel trims bouncing all over the place-- at least I think so. I don't know how quickly the O2 sensors cause the computer to react and then command the fuel injector to add more fuel. And that still doesn't explain why its the LT and not the ST trims that are jumping, but I have n o earthly idea how the ECU is programmed. I suppose a bad ground or wire somewhere could be the culprit. Further down on my list of things to try is running new grounds to the ECU.

 

65 mph steady


Idle in drive

 

cruising steady speed (but MAF is higher than previously so don't know what that was about - maybe before I was decelerating). Note this one has EGR position fully open (99.2%) and IAC position fully retracted (198 counts)

 

I really wonder if Torque is monitoring things right. Even the famous Torque is not infallable!! You should be able to get Car Gauge Pro to agree with Torque for the Generic OBD2 PIDS such as O2 sensor, STFT, & LTFT.

Once you get significantly above idle, the IAC should retract fully as shown in the screen cap right above this message. Then catch and control the idle speed as it comes back to idle. Mine was max 198 counts - min 106 counts (as shown in the gauge). that's all it really does.

 

I might give Car Guage Pro a try. Do you know if all the monitors you have in your screen shots come with the base app? I looked at the GM pids the other day when you first mentioned it at it looked like it was $100 for just those pids.

 

The pre-cat vs post cat O2 sensor thing is only tested at >2000rpm so nothing to be said for being the same at idle.


the time frame for PCM to adjust to O2 sensor readings has to be pretty short or you would set code for O2 sensor being rich or lean. I believe PO171 allows only 120 seconds total for PCM to get fuel mix under control before setting the code. Response time has to be much less than that.

 

Car Gauge Pro is $8.95 and comes with all the PIDs that they have (at least it did when I bought it). However, Car Gauge Pro will not do any of the enhanced GM PIDS that comes with it when hooked to the 1996 and 1997 Vortec engines. However, it will work fine in Generic mode on your 1996 to display STFT, LTFT, O2 sensors, other basic OBD2 PIDS. I thought that you already had it? The only thing it will do that Torque will not is the cam sensor retard, and that doesn't work on your 1996. So I wouldn't buy it if you don't have it already. If you want to buy one, buy Dash Command + PIDS for your year ($10 + $10 more). That will get you the cam sensor retard too and the enhanced PIDs will work on your 1996.

As I understand it, there is something different about 1996 and 1997 computers. I think it is described by color of the connectors. Torque may not be reading yours right (there is definitely a difference for Car Gauge Pro). But if you check Torque against another hand held scanner, then it is certainly verified for that particular PID. I just don't have any experience with the older 2nd gen Blazers.

Maybe someone else can verify that Torque works or doesn't work correctly on 1996-1997 Blazers.

 

Sorry, I was confusing Car Gauge Pro with Dash Command. Yes, I have Car Gauge Pro. I had the trial of Dash Command at one point and liked it. I thought the PIDS for it were $100, but if its only $10, I'm going to get it. I find Car Gauge Pro very flaky and difficult to use. It keeps disconnecting me from my obdii connector and its frustrating. I was able to use it to set the 98 5.7 Vortec cam retard, so I guess it paid for itself, but it has no support at all from the maker. I also find that it will pull up history codes and some manufacturer codes that Torque will not. Torque has a pretty good interface, imo, but so does Dash Command. And if I can get all the pids for my vehiclefor $10 extra, I'm going to go that route. I've noticed on Torque that I can clear codes without resetting all the IM monitors. That's pretty handy, but I don't know how it manages to do it.

The 96 to 97 computers went from a red security clip to a blue security clip. I'm not sure what else got changed or if the white/blue/clear/black connectors changed. The airbag came out in 98, so for those the programming at least is going to be different. But from what I've seen on ebay ECMs, they'll flash the ECM to your VIN and the same computer seems to span a fairly wide range of years.

 

Somewhere in there they started using BCMs and did the auto 4WD where TCCM communicated with the PCM. Looks like maybe when all the modules went on the same data bus. I have heard that 2001+ "411 -suffix" PCMs will work on older vehicles but not vice versa, if properly programmed. Also I believe that pinouts may be different. That's all above my pay grade.

One thing about Dash Command. They will get you $10 for the software + $10 for enhanced PID for each year and maker the app is used for (you buy enhanced PIDs for individual years and manufaturers). Effectively each vehicle. Apparently they must actually license the PIDs from GM (I suppose why they don't offer them for free along with the software). Buying Scan XL Pro (another product they have) and then GM enhanced gets you all the PIDs that they have for GM, but it's $80+ extra onto the $150 base price. I do have a 2006 Pontiac G6 (first year of CAN protocol) that only the Dash Command app and Scan XL Pro will connect to and do enhanced PIDs (Torque wont connect at all, and Car gauge Pro will only connect in generic mode). Dash Command seems to always work for the oddballs that the less expensive apps have trouble with.

I like Car Gauge Pro best myself (in general), but agree that the user interface is kinda poor and user info is entirely self taught. Once you get the hang of it and know it's benefits/limits I think it's pretty useful. I use it on my 2001 Blazer and my 2004 Avalanche. But tons of modules to chose in the interface that simply will not work on most vehicles (especially an older Blazer). Nothing is filtered and disappears because it doesn't work on a particular vehicle. Did you know it was actually reading ABS PIDs on my 2008 Ford Ranger? I could even read individual wheel speeds. This is not a capability on my Blazer. It's supposed to be made for Ford and Nissan - just happens to work pretty well on the Blazer Powertrain PIDs and does the cam sensor retard on the Vortec engines (something Torque and Torque users have never been able to figure out).

 

I was right about the STFT. It does cycle up and down with the O2 sensor, but doesn't seem to do it at idle. This is at 2000rpm in park from tonight. I saw it cycle from about -5 to + 3. So Fuel trim response time seems very fast