Running Strange, 4.8L/DBW/1MB/4L80/12592433 OS

[RADustin]

Working on my brothers truck. It's the thread title swapped in a '67 GMC.

Currently- 4.8L/DBW/1MB/4L80/12592618 OS

Pedal and tac are 2005. Motor/PCM was originally 2007 classic. Swapped tac when we changed OS.

The truck revs really strange(slow) and makes no power driving it around. If I tip in the throttle quickly(snap it open and let it shut), but only to 30-40% absolute, it will jump to 100% commanded on the tech2 and snap back. If I tip it slowly it will slowly climb and seems ok.

Getting no codes, no reduced power. Scanned with tech2, everything 'looks' OK.

Mentionables-
-Idle TPS seems high. about 12-14%.
-Idle airflow seems ok- about 8-12g/s depending on temp. reading from MAF. VE has not been tuned.
-CASE relearn is complete and seems OK.
-Startup airflow is not working. No matter how much I add in startup friction and startup correction, it does not flare on start up but rather stumbles to life.


Questions so far-
-How is startup throttle blade position calculated? Why can't I get the engine to roar to life like I can my other ls1 with too much startup airflow? When I command say 12g/s on startup, basically how does the engine set the blade to get this amount of air? I imagine it uses cranking VE maybe with MAP and IAC info???

-Has anyone experienced this? Is it probably trans related or engine?


Just really messing with my head- I can only imagine it is a physical problem with the engine/trans or the pedal/tac/OS relationship is off.

Next we are going to flash in a stock tune file from a 6.0/4L80 with the same OS. See how that works. Basically I think the plan is to keep going backwards eventually to the original tune that last ran on the truck, even if we have to swap back to a different OS and tac module. Just want to ensure nothing is physically wrong with the truck before we assume it all to be electronics. Then once we verify that it is just the pedal/tac/OS/tune file issue we will have to narrow it down from there.

Any ideas? Suggestions?

[ScarabEpic22]

Post the tune and a log please, happy to take a look.

For pedal/TAC/OS, are they all from a truck/Vette? I.E. no mismatches?

[RADustin]

Got it.

Combination of crap plug wires and a wiring harness issue.

Weird it never threw any misfire codes or similar.

[turbo_bu]

If you hadn't had a chance to do a CASE yet, (most likely not with all the issues you were having), then I don't think it would have been able to throw a misfire code.

[joecar]

More info on the problem and the solution...

[RADustin]

Did a CASE relearn and it took.

the ONLY clue that something was messed up on the motor physically was the fuel trims were way imbalanced. But- the side it was heavy on also had an exhaust leak so we weren't sure if it was a reliable reading or not. The same side had a luke warm exhaust manifold though so we knew it was ignition related as the engine had fuel and compression.

after trying a bunch of tunes- went back to the basics and found 2 failed plug wires. Fixed those and it still seemed 'off'. Then found an intermittent ground issue on the coil pack harness. Ran a temp ground for now and its running strong.

Back to tuning finally.

[ScarabEpic22]

Gah, hate it when those things come up! Especially "fun" when someone drops their car off for a tune and you spend hours and hours correcting physical issues so you can even start tuning.

Glad you got it squared away, post up a log of the finished product!

[RADustin]

yeah good thing he is blood or he'd be sent to the other side of the wall

can't wait to get the blower on it. The 4.8 is strong, stronger than the 60e that was behind it. The built 80 should be enough for the blower combo though.

[joecar]

You can't charge the customer for any physical repairs you do... the customer just won't accept it.