I drove the truck to work yesterday morning and all was fine. Left yesterday afternoon truck was still fine then about half way home I got into boost and the truck falls on it's face. I hooked up the PC to see what was going on and it is dropping timing to nothing at 90ish Kpa. I thought maybe for some reason it jumped over to the low octane table but it is even lower than that. At some points it is pulling as much as 33* from the commanded HO timing. Everything else looks fine and the truck feels as it should under 90Kpa. Any ideas, or is this just a fluke PCM issue? I have attached a screen shot comparing the scan to my LO table for reference.

 

THeres lots of tables that will pull timing, IAT ECT, burst knock

Ive had problems with burst in the past, and the truck will straight fall on its face pretty bad.

 

Log all of the timing retard parameters one see which one is pulling timing, I think there are 4 or 5

 

I did some more logs yesterday logging all the retard and advance pids. I am getting some burst knock once I approach 100kpa (assume when the bypass valve is closing). Add that to the base timing from the low octane table and the instante 8*KR I get when the timing plumets and an AFR of low 10's, it equals my actual advance of 5* to -15*. I filled the tank (19gal) hoping it would revert back to the high octane table but it didn't. Even though I am running a 2bsd os and don't use fuel trims, will resetting trims via the scanner controls reset the timing table reference? Is there a PID that shows which table it is using so I can confirm?

 

I think I was having a similiar issue and it had to do with one of the sanity check tables which I had to raise. Im not on a computer with hptuners right now so I cant look

 

I did a little research on HPT forum this morning and have a little more insite. I need to check the Knock Learn Factor to see if it is in the HO or LO tables. 1.00 is 100% HO, 0 is 100% LO. The KNF does not completely reset with a fuel fill, it takes about 10x longer to learn up than it learns down. However Burst Knock does not contribute to KLF, just Knock Retard. I also need to check for a MAP code to make sure it is not out of range as I did recently swap to a 3.25 pulley before going to the track last weekend but haven't driven it much on the street since. The temp also droped about 20* on Friday when the problem first happened. So tonight I will be coping over the HO to LO, checking MAP table ranges and adding Knock Learn PID to the config and trying again.

 

Flashed a new tune in with HO copied to LO table and burst knock raised to .5g/cyl and everything is running great again. However, KLF is rock bottom at 0.00 and didn't move the whole time I drove it tonight with no KR anywhere. :dunno:

 

You wont have any learn if you dont have any knock...which is good, after all.

 

0.00 is 100% in Low Octane table. I figured I would have seen some reversion back to the HO table. I am going to leave it as is, keep an eye on KR and see if the KLF starts going back towards 1.

 

I would pay more attention to what your actual timing is compared to your two tables as opposed to the knock learn factor.