Help with cold start for big cam 408 aftermarket TB

[RonSSnova]

Hi all,

I'm trying to help a friend who is across the country with cold start on his modified 408.
Cam is 245/255 112 lobe sep.

BTW, he is in Florida, so cold start is still rather warm........

The TB is an aftermarket 95mm Cable driven. The IAC motor is stock GM.

The previous tuner changed the IAC steps vs effective area quite radicall. Tune attached.
The counts max in the table are now set to 102. Stock is 310.

I can see from the cold start log that the IAC goes straight to 102. Car will not start w/o adding pedal for a few seconds.
Once it warms up, the IAC counts re between 30 and 40, which is fine.

My thinking here is that no matter how much start up airflow I give it, the IAC cant add more than 102 counts. Am I correct?

I have to say that when I started with this, there was no RAF curve, In gear was set to 50g/sec across the board for in gear. P/N was set to 6g/sec.

I guessed at a curve, which helped. And even though he needed to add gas for a bit to get it running, I was able to run the Russ k idle setup and get numbers that I then put back in the P/N RAF. I filtered out TPS above .5%.

Doing this long distance is tough because I'm not hands on. But we are making some progress.
I am not sure where the throttle blade is at 0 TPS. That all may need messed with too......

My next step is to return the IAC table bck to stock and see how it does.

Am I on the right track?

Lastly, the truck is currently running MAF only, it is a card style MAF, and I know the MAF is not yet properly calibrated.......

Cold start log, config, and tune attached.

Ron

[mowton]

Based on the size of that cam, you may have to increase the TB plate hole to bring the IAC count down during cold start. You need to make sure that during closed throttle, the TP sensor isn't outputting more than say .65-.70 volts (650 to 700 mv) as well and that is where the hole in the Throttle plate will come into play. You will need to continue to adjust the set screw until you get to the .65volt area.

Yes, 102 steps is the max so I would reset that table back to stock, If you need to let more air in after the IAC count and adjusting the Throttle plate set screw, next comes the hole increase. You will see there is a hole included from the factory on drive by cable setups. Go in very small size increase increments.

I would bring the tables back to stock and then address each based on the cam influences. Its a big cam and is really inefficient down low so actually less air may be better.

Ed M

[RonSSnova]

Thanks. I just put TPS volts in the config to see where it is currently. I know it has been messed with.

On my nova, I slotted the tps mount holes so I could keep the tps in range.

I'll change that table back to stock and have him do another cold start.

Ron

[mowton]

Where in Florida

Ed M

[RonSSnova]

I actually don't know!

Good news, I changed the IAC table back to stock, it fired right up cold.

[mowton]

Maybe this will help.......

http://www.gmtuners.com/tech/TPS_IAC.htm

Ed M

[mowton]

I actually don't know!

Good news, I changed the IAC table back to stock, it fired right up cold.

Very good, I actually like working on drive by cable setups because they make you think......drive by wire has its issues as well but IAC counts, holes in TB plate and set screws provide an interesting playground......

Ed M

[RonSSnova]

Thanks. I used that info when I set up the TPS on my nova. TPS sensor was already slotted. It worked well.