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Friend of mine built a 5.3 rcsb truck that was a v6 manual. Since the truck has been done it has always had this odd stumble when you first take off cold. It only does it once then is perfect after that. In the log you can see at 57.6 seconds it pulls all the timing out of it. Anyone have any idea why looking at the tune?Attachment 160584
Attachment 160585
What modifications have been done? what fuel injector part number? vacuum referenced or fixed pressure regulator?
Cam, long tubes, 42# injectors 25348180, vacuum referenced rails. It did it with the stock 5.3 injectors as well.
Ah the 8.1l marine injectors. You should use injectors that have proper characterization data for your PCM, it may work, but it ultimately will never be "right", and the complaints are always weird little quarks like you describe, there is much more to the injector data than just the 42lb flow rate. Have you logged your idle air adapt trims and updated the BRAF table for park and in gear conditions? I would also go back to closed loop, i am sure the airflow models need work, but you should select injectors with proper Gen III GM data first. I know this is the answer that nobody wants, you have to be very meticulous about this stuff, these factory PCMs have been extensively engineered for driving quality and smooth operation, and have tons of adaptive features for many different parameters, such as the fuel trims and idle airflow trims, use them to your advantage.
Its not in the fueling. Like I said in the first post it pulls 25+ degrees of timing for a split second when it falls on its face and then ramps it back in. Also like I said it did it even with the stock injectors in the truck. Its not fuel related.
My thoughts are, wideband shows rich, idle and off idle, engine is cammed so it is likely even more rich than the wideband is reading, with the cam, they tend to cause widebands to read slightly lean, it over fuels during the transient from idle to off idle, overspeed correction pulls timing to correct the overspeed, this would be amplified if your BRAF has not been adjusted.
Try logging all of the spark advance and retard PID's and see if it shows where the timing adjustment is coming from.
Just noticed, right before the dip in the ignition timing, your fuel injector pulse width drops to zero. This only occurs this one time after the engine is running.
What should I look for on why it pulls the pulse width out as well as timing? I will log all the ignition stuff and see if I can catch it.
Ya, that's interesting. Something is trying to pull the rpm down, even though the TPS is registering throttle input above idle. Is this a patch together of OS and segment swaps?Quote:
Originally Posted by twenglish1
Definitely strange, no idea what would cause it to cut fuel like that, and also be so repeatable, not looking right now but if i remember it was a speed density custom OS
Could you post your original file before modifying?Quote:
Originally Posted by 94heritage
Yes I will post the original when I get home. The original file was just a 6.0 manual file from the repository. It did the same exact thing with it running regular maf and closed loop. I switched to speed density custom to try and fix the problem
Here is the stock file I got from the repository.
Attachment 160710
There are a bunch of odd changes like you blindly copied out of a 5.3 file or something. If you don't fully understand the table/change it's likely best leaving it stock even if your sample file is from a different engine.
Try this.. This was the most glaring.. that don't look right table.
Attachment 160721
The spark retard limit table I changed because it was pulling so much timing when the stumble happened. I tried taking it from -10 to +10 just to see if that would keep it from pulling all that timing out. The other tables that normally wouldn't get changed I did as you said I copied them over from my known good running 01 5.3 auto truck with very similar set up to see if any of that fixed it. No matter what has been changed it still does the same thing only once from a cold start and then it never happens again until its cooled off. Truck runs and drives great other than the initial stumble. Its just really annoying and it is "violent" enough that its really irritating
Dont think it is tune related but i changed some things.
yeah don't do that.. That literally leads to problems like this. I'd start back from that 6.0 completely stock file and only change the basics.Quote:
Originally Posted by 94heritage
Yea I don't normally do that stuff. I only copied all of that trying to fix this issue since I knew that my truck didn?t do this. It started off with just the stock file but its done it since the truck was built.Quote:
Originally Posted by Alvin
Would you happen to have a different manual truck os for a 99-02? Just need a stock file.
Why not use the stock 6.0 manual file you posted here?
It started life as that file. With just your standard changes to idle, braf, start up air, ect?. To get it to run with the cam. Then started working on the maf and ve table to get fueling correct. It has done this stumble since day one. Ive since changed all of the other tables over from the 5.3 tune just to try cure it. Turned off the o2s and switched it to sd os just trying to see if there was any sort of change.Quote:
Originally Posted by Alvin