When in open loop and running the MAF the car starts and idles fine. However, in open loop SD i start the car and have to hold the RPMs at around 800-100 for a little bit or else the car struggles to keep the rpms up and dies. What tables should I look at adjusting to correct this? The car is an LT1 and I'm using tunercats.

 

You need a wideband to check your AFR, but it probably needs the VE table leaned out some in the idle area...

 

i do have a wideband. i believe the afr on initial startup is around the same when i have the maf in use or when im using SD. would SD require less fuel to startup then it would in MAF mode?

 

No, fueling requirements should be the same. If AFR is the same, what about timing? It is going to go to the low octane table in SD... You will need to copy the high octane to the low octane to have the same timing you do with the MAF hooked up... Edit: You may want to look at the idle timing tables as well - not sure what you have available with your software, but I generally copy the applicable portions of the high octane table into the idle spark tables as well.

 

^ What he said.

 

On older LS1s, MAF faults put you onto the secondary
VE table. So you would want to know if this happens
on LT1s too, and if so, keep the secondary tight with
any changes you make on the primary, and vice versa

 

The LT1s have the VE table split by RPM (they call one VE and one extended VE), but they don't have a secondary VE table like the early LS1's...

 

An LT1 has another problem when you run an open loop tune. It has what is called "keep alive" BLM's in the ECM Constants menu.

The low value here is going to be the initial assumed BLM or fuel trim (for all the fuel trim cells) upon startup after flashing the PCM in an LT1 car. Usually the minimum is set to 120, but closed loops target is 128...so the numbers in the VE table will be scaled incorrectly by this amount.

That said, up the minimum keep alive BLM to 128...it might help what you're doing...of course you will probably also need to re-scale your VE table if it's completely "tuned" already.

 

the lt1 software is a little different the equivalent of copying the high octane table in an LS1 tuning suite is zeroing out the low octane table in tunercats for the LT1. My data logger shows the same timing between open and closed loop. what function is the MAF serving during open loop that wouldn't occur in an SD open loop?

 

isnt the keep alive BLM not functioning during open loop as the O2s are not providing any correction? During open loop my BLMs are all at 128. i'll look at my min keep alive BLM to see what it is set at.

 

Your short terms might be at 128, but I bet your long terms are at 120 (or whatever is in the keep alive constant)...ANY time I flash an LT1, it runs the long terms at the keep alive until closed loop enables...which in your case never happens.

LT1's work differently...your spark advance has nothing to do with your MAF sensor...it's entirely MAP/RPM based...same goes for low octane...it's all how much it can pull...not a new table for it to run off like an LS1 is.

I'm not THAT far away from you in MA, send me a PM if you'd like some help, I've tuned more LT1's than LS1's.

 

I just checked i have the min keep alive BLM set at 128 in my tune. I'm going to try to lean out the VE tables some more in the very low MAP and rpm values to see if that helps. i did also notice that all blms are at 128 short and long term.

 

That makes sense...the factory keep alive min value was 120...someone upped it to 128 on purpose...thats ok.