Tuning for a rich 305ci sbc

[brettinator]

Edit: posted this before i saw your response
Thank you and i definitely will move it in the morning [Heres further confirmation that the MAP sensor needs to go on a different manifold vacuum port than stock. Helps to read! Who would have thought]

You must be registered for see images attach

 

[brettinator]

You definitely want to move the MAP port. The rear port opens right to the IAC passageway. If you follow the passageways you will figure out the difference. The GM MAP port is away from the IAC vacuum leak, where the Holley MAP port dumps right into the IAC vacuum leak. What that means is lower vacuum reading to the MAP anytime the IAC is open. What happens on a cold start is the IAC opens, the vacuum to the MAP drops, the MAP drops, the ECM overfuels the engine, which then causes the ECM to open the IAC even more which causes it to overfuel even more until the system is just dumping fuel and the IAC is wide open.

Holley

You must be registered for see images attach

GM

You must be registered for see images attach

Excellent. Thank you

 

[L31MaxExpress]

Edit: posted this before i saw your response
Thank you and i definitely will move it in the morning [Heres further confirmation that the MAP sensor needs to go on a different manifold vacuum port than stock. Helps to read! Who would have thought]

You must be registered for see images attach

I usually use the one on the front RH side for the vacuum port. It makes the vacuum line to the MAP as short as possible so that it responds as quickly as possible.

 

[Schurkey]

Biggest issue with the Holley is the vacuum port on the back should not go to the MAP. MAP needs to connect to the manifold vacuum port on the front. The rear port is connected to the IAC passageway and causes the MAP to read wrong especially on a cold start.

Thank you for this.

I bought a used and abused 502-6 Holley throttle body listed for my '88 K1500 5.7L years ago. Never got around to installing it. Still sitting in the box in the shop.

SOMEDAY, when I put the thing on my truck, you will have probably saved me substantial headache.

Thanks again.

 

[brettinator]

Hey yall,

The update is:
I moved the MAP sensor to the LH vacuum port in the front and capped the rear fitting. The only reason i didn't use the RH barb is bc EGR is connected and the line is too short to reach any other than the one it's on.

Finished up my driveway cat back exhaust today as well.

First couple starts were rough. Wouldn't stay idling and felt shaky (like an imbalance). But I think it adjusted and started idling better and running smoother.

The exhaust is heavy smoke still, though. Waiting for the heated o2 sensor to add that