That wouldn't explain the split BLM's (LTFT) - adding fuel on one side and subtracting fuel on the other. The knock sensor would pull timing, but that's just going to produce a small power loss or surge. The loose bolt could explain the rough idle. But there is still something affecting each bank of the engine individually. Not something like a dirty MAF sensor, incorrect fuel pressure, large vacuum leak, air bypassing the MAF sensor - those are things that would affect both sides of the engine equally.

If you feel it's running to your satisfaction, the engine will run "OK" but possibly not at it's peak. If you have spare time, try swapping the pre-cat O2 sensors side-to-side to see if the "split" follows the sensors. If not the sensors, swap the injectors in a complete set of 4 side-to-side. See if the split follows the injectors.

In any case, just to close things out, could you run another data log on the same manner you did the previous one?

 

Fred
Here is the latest log. I had 2 new Denso pre cat O2 sensors in my stock of parts and because I already had the car up on my quick lift I went ahead and changed them out. I also installed my Energy suspension rear spring insulators to get rid of a persistent spring rattle I had in the rear when going over a bumpy road since I finished the car in 2019 which is gone too so it was a good day. The car is running as it did before the problem started. It idles smoothly and no more rough acceleration. One other thing I will add is that the problem seemed to have started after filling up with Chevron Premium for a drive on Fathers day when I had previously always filled up with Speedway Premium. Let me know what you think looking at the log. Thanks again.

 

The O2 sensors must have straightened out the "spli" BLM problem. Now the LTFT's are similar on Bank 1 and Bank 2, although they are still adding an excessive amount of fuel (+9% Bank 1; +12% Bank 2) at idle. And the added fuel is similar any time you put the engine under load, adding 10-12% on both sides.

Check for air bypassing the MAF sensor - bottom of the bellows not over the throttle body, crack in bellows. Make sure MAF is clean. Check the fuel pressure.

Most people seem to get the best results with AC Delco O2 sensors. The factory service manual cautions that anything other than factory replacement O2 sensors may change the results of diagnostics like the catalytic converter efficiency analysis, because they have different response characteristics, apparently due to response times.

 

Thank you... I will keep checking to see if I can track down any air bypassing the MAF. I'll respond if I find anything.

Tim

 

Fred
Scrapped that GD scan software. I think that software has issues and at a minimum its got serious bugs! It was reporting way off from the live data I was getting on my hand held and I had not looked at the DTC tab before but it was also showing some codes. I rechecked with my handheld code reader and it showed no codes, ODBWiz showed no codes, I thought maybe the car was going to hell but I was able to get my mechanic friend to bring by his expensive scanner and it showed no codes. I did a clear just to be sure and GD scan showed the same codes again with all three other scanners showing no codes so something is up with that software. Anyway I did find a small vacuum leak. Up near the firewall is a small valve for the AC which I think controls the vent positions. It has a small tube that plugs onto a port on the intake. The end of the valve had cracked where the hose attaches. Luckily there was enough left of that end that I could remove the cracked part and still press the tube fitting on and was able to pull a vacuum with my tester. I downloaded Easy ODBII and we compared the live date from that software to the Snap On live data at idle and it was pretty much spot on between the two so I am confident this software is reporting accurately. I did one more scan of the fuel trims with the same drive parameters if you want to take a look. I don't see any negatives so that vacuum leak fix definitely made some difference. Let me know what you see now. The car is running extremely well. Thank you - Tim

 

Looking at your new log, it's still adding excessive amounts of fuel under load. Yes, the idle LTFT's are down, but that reflects the elimination of the vacuum leak. The new log has less data, particularly throttle position, but what is there is entirely consistent with the "GD" log. You're the first person in all these years to question the validity of Gary's software. I'll ask him to look at this and see if he sees any value in pursuing your issues.

Where did you find the codes in GD? The log you sent me says (column B) there are "0" codes.

What does this mean "I don't see any negatives so that vacuum leak fix definitely made some difference."? A vacuum leak causes positive LTFT's, not negatives. This latest log shows that the PCM is having to add fuel under load. Since you apparently reset the PCM before this log, it is still using the STFT's to correct the need for extra fuel. Looking through it in detail, you are adding up to 20% extra fuel (or more) under load. Normally, you should see the STFT's moving back and forth between positive and negative. This is how the PCM assists the operation of the catalytic converter. But your STFT's never go negative - maybe your new software doesn't use the negative sign. But because you reset the PCM before the new log, whenever you go into a new load cell that has not been driven in for a significant amount of time, the PCM has to use the STFT's to make the correction. If the PCM sees it is adding fuel all the time (all positives) with the STFT's, it starts to ratchet up the LTFT's to drive the STFT's back down so the average "0".

My conclusion is the same - yes, you corrected the first problem with new O2 sensors..... a problem clearly pointed out in the GD software. Then, you found the vacuum leak that appeared in the GD data. But you still have a problem with the engine running short on fuel under load, and needing the LTFT's elevated to add the required fuel. But that doesn't seem to matter to you.

At this point, I don't see any need to carry this thread any further..

 

The negatives comment was an error on my part. The codes were on the DTC tab. It seems that this information could send someone down an unrelated rabbit hole since they are erroneous and could not be repeated in other scanners even a very sophisticated one. I myself almost spent 50.00 on a crank position sensor due to one of the codes but thought to double check first. Gary stated that the software likely had bugs in the post you provided to download it and that post is from 2012 and the current install file is 5 years old....

There are sure to be many bugs, so make sure to let me know what does and doesn't work. And what you like and don't like about the program.
You can reach me via messaging on FBN (GaryDoug) or email at: garydoug98ta@gmail.com.

I'll end the thread here. Again thanks for the assist.