Greetings,
Trying to dial in my TPI swapped Sub w/ orig 6395 ECM and 0D mask.
Can anyone explain the 'stall saver' functions?
Would love to have someone in SoCal help me try to smoke the tires on this 8000# Tow vehicle!
Thanks

 

First which transmission do you have 60E or 80E?

Here is my 305 TPI powered tow vehicle.



I know first hand your timing table will have a huge dip in it around 3,200 rpm due to the TPI. The VE table will have a large plateu there as well.

 

Nice! I've got a 4L60E behind a TPI Vortec stroker. Howell Eng. in MI did my harness mod and burned a chip. Runs decent, but now I have Autoprom/Tunerpro RT and am trying to educate myself on tuning. Compared my tables w/ orig bin, see minor differences. In regards to the flat spots you expect me to see, I may not be well versed enough to see that in the data, but I believe I need more PE especially for WOT. BLM's run very well throughout (124-134). My other issue is a flucuating idle; been reading posts about this relating to milder cams. Any thoughts?
Much oblige!

 

IIRC, the stall saver functions are done as a percentage of the desired idle speed. IOW, if your idle speed is 700 RPM, and the stall saver engage threshold is 70%, the stall saver will engage at ~490 RPM. Once this happens, the IAC is rapidly opened to prevent an engine stall. There is also a threshold for exiting stall saver that should be higher than the engage threshold. Once the engine comes above the threshold, the extra IAC airflow is decayed out so the engine can return to normal idle speed. These wont cause a fluctuating idle. It would likely be more of a rapid up and down surge as it goes in and out of stall saver. The idle is controlled through the proportional/integral IAC airflow terms as well as derivative IAC airflow, derivative/proportional spark, and derivative fuel. Any one of these could be off, and would cause a surge or instability. An up/down surge is more likely one of the proportional terms while general fluctuations would be more likely to be the derivative terms. The fueling being too lean at idle or the proportional O2 gains at idle can also cause the engine to surge.

 

Wow! I'm absorbing and interpreting! Question: Can i determine which proportional terms may be off by datalogging or do I start tweaking certain params. in the bin?
Thanks

 

Is this a red Suburban and you came by a few Saturdays ago and asked me questions about it?

 

There are several things that can cause a fluctuating idle on your setup. The first thing that comes to mind is what make and size injectors are you running? The TBI and/or CPI injector offsets do not work well for port injectors othet than the pico style and even then they need some tweaking. The second thing that comes to mind is that you might be running that TPI setup on a TBI injector firing scheme. If Howell just did a basic "Edelbrock" type PFI conversion, then a fluctuating idle is a common issue. The last thing that can cause this is the "Idle Overspeed/Underspeed Spark" tables. Once the cam gets over about 218 duration @ .050 or so or the LSA gets narrower than 112, these tables need to be tamed down and the idle speed needs to be increased. HTH

 

Yes, this was the red beast at Don's shop. It was great meeting you and your dad! Waiting to attend your tuner classes it has been suggested you lead!
Thanks again.