Hey guys,

Just slapped the new 454 TB on tonight. One thing I noticed (after having to figure out the wiring for the IAC, which I was suprised, was HARD to find the answer to, in here, I'm going to PM shifty with some pics and info on the IAC wiring).

Anyway, things run like a champ, the only thing I can't figure out, is during start up. It starts hard now, I have to give it a bit of throttle to get it to catch, then slowly back off until it gets its normal idle. Once it is there, it is great, drives like a dream.

Looking thru the chip trying to find what it could be, I was surprised that there was not much startup stuff. Can someone shed a little light into the interactions of the start-up tables? I would really be interested in the IAC stuff, as that seems to be the only real change I made. Does the IAC stay in the park position for a period of time, before it will actualy take over, and start trying to catch the idle, would moving my park position, effect the start up? The only other start-up stuff I saw, was choke AFR, and cranking AFR stuff, most of it was tied to coolant temp.

Thanks,
John

 

There is also the crank AFR table at $36F. This defines the desired AFR during cranking. The SA is at the distributor base during crank.

On the 454 TBI unit the IAC port is larger then the smaller units. This means that at the same IAC setting more air will bypass the throttle blades.

During cranking the IAC will stay at the defined park position. And will move to a new position once the engine RPM exceeds 400. This movement is rapid. Under cold conditions it can actually open more then the park steps. Warm, it usually closes down from the park position.

One thing that will help is to reduce the IAC steps during a warm idle. By warm I mean up to operating temperature. Open the blades until the IAC steps are at 5-10 steps. Then reduce the IAC park position in the cal.

The result is that during cranking more air goes past the blades. This helps draw the fuel into the intake manifold.

RBob.

 

Rbob,

which direction is the park position? Currently the park position is set at 160. once i get the car started, the IAC counts are at about 30-35. Should I try to change the IAC park, to say 35, or would I try adjusting the throttle blades, until my IAC counts are even lower?

I am not sure how the datalogging works. are the IAC steps, the change from the park position?

--John

 

John,

The IAC Steps are from the 0 or closed position. For reference fully open is 255 counts. So the IAC steps are from 0-255. You need to set the park position around 45 or 50 steps. Also revisit the IAC Position vs. Coolant table. The IAC Park position is simply where the ECM places the IAC valve. The ECM quickly moves the IAC valve from the park position to the desired location based on the coolant temperature. From there the IAC logic in the ECM adjust the IAC position to close in on the desired idle RPM based on the Idle Speed vs. Coolant temp table.

 

Right, but this is during cranking, once i get the car running, it will keep the idle, but it takes a little work with the throttle to get it started. I'll try changing the park position to say 40, just to see what I get. I never modified the park position with the new TB, so I did assume I needed to close it more. As for the coolant temp table vs IAC position, i assume i am going to need to change that also, as for each IAC step, this setup will get more air.

I'll start playing with, I was really just looking for some clarification on what the computer was doing with the diffrent tables.