Hi Guys ,

Need your help. Ok here is a rundown of the problem :

We built a 2008 GMC Sierra 1500 with the following mods :
418 L92 , D1SC @ 14 PSI , 4L80E Swap controlled via a TCI standalone Trans Computer . The swap involved us having to custom cut the driveshaft on the vehicle . The new one isn't perfect but does the job. Side Effect is that it does vibrate at high rpms. Another side effect is the we had the factory TCM unconnected . The same caused the following ECM/TCM Errors :

ECM U0102 ( Cancelled this via Hp Tuners )
ECM U0109 ( Cancelled this via Hp Tuners )
TCM P0787
TCM P0961
TCM P0973
TCM P2764
TCM P2769

The first two we cancelled the rest we couldn't. What happens is this , when we gradually increase throttle input Timing drops down to very low levels ( 4 degrees in the latest scan ) while KR gradually climbs ( 7.4 degrees in latest scan ) . Our theories behind the same :

1- The TCM DTCs are causing the drastic pull in timing ?
2- The makeshift driveshaft is causing vibration severe enough to fool the knock sensors into pulling so much timing ?

For reference WOT AFR is @ 11.1 ( we are still fine tuning it , so keeping it at this level to ensure safety and no Knock )

 

If you, or your customer, is spending all of this money on building a badass engine, why doesn't he spend a few hundred on a built, high-speed balanced driveshaft? It's going to cost a lot more if it lets go on the dyno or on the street.

 

Unfortunately when building the truck we knew this would be a problem. See we live in the UAE and having one built in the US wasn't going to happen unless the install was almost done. So we decided this , make a makeshift one , then send the specs to our guy stateside for a better one ( This is in progress now ) .

So yeah we agree the Driveshaft is a problem . So you think this is causing the timing pull ?

 

Oh, that sucks. Hope you get that sent your way.

Right now, tuning is over my head, but there are many smart people on here, so I am sure someone will be able to help.

 

That'd have to be one hell of a vibration.

I'd bet that the Knock sensors have to be de-sensitized in the PCM because of the cam and engine. If they detect a knock they will pull timing like crazy.

At least that's what happened on mine anyway.

 

torque management tables play heavily into this. there is more to the tune that can be seen by the hpt software. something might be getting triggered in the background. i have delt with this before on several cars.

soften up the knock sensors and the misfire tables and see if the timing comes back around. 4 degrees of timing is just evil to the motor at wot. egt's are skyrocketing