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I'm running an LS3 with a top mount (4150 style) throttle body and controlling with an early (2001) GM ECM. (24 pin crank, 1x cam sensors). Both crank and cam sensors are new. when
I have 60 psi of fuel pressure when starting, but as the engine starts it sounds like it coughs first, then starts, or it often turns over way too many times prior to starting. The tune on the engine has been done properly by the best GM tuner in the area, so I'm thinking it has to do with the ECM not talking correctly with the Holley throttle body which includes the IAT, TPS, and IAC are all part of the throttle body.
I should note I'm using a GM 12569240 remote mount MAP sensor that has a vacuum line to the TB. Does this need to draw vacuum from a "timed spark" vacuum port or from a "full manifold" vacuum port? I currently have it hooked to a "full manifold" port can can't find anything in the Holley info that tells where to pull vacuum from.
If anyone has a set-up like this and has had good luck, I would love to hear from you. Thank you!
I'm running the same computer as you and also running the MAP off a central intake port. No problems with starting and tuning there. It prob just needs some slight tuning changes.
Hi CW, Yes I manufacture this item, IAC, MAT, TPS AND NOS.
This item was flow tested by Steve B. at Westec back/back using a 4250 which I beat by 15 cfm.
The bore size is 2.5" x TWO butterflies = 1200 + CFM.
I made 650HP (416 benched) when my TBI was fitted, calibration was simple.
I appreciate both responses I've received but I'm really simply trying to determine which vacuum port is the best to connect to for the LS1 style MAP sensor? Should it be the "timed spark" or the "full manifold" port? Thanks again!
MAP= Manifold Absolute Pressure. Straight manifold vacuum is required here. No "ported" stuff. That is strictly carburetor emissions era spark vacuum technology
MAP= Manifold Absolute Pressure. Straight manifold vacuum is required here. No "ported" stuff. That is strictly carburetor emissions era spark vacuum technology
couldnt be more wrong with the "carburetor emissions era spark vacuum technology" statement. The map sensor for the op's engine and today factory boosted engine work on the same principles and in basically the same spots. Which is anywhere in a central comman area of the intake, not at the bottom of a individual intake runner but anywhere in or near a central are of intake for lack of better worlds. The intake should have at least 2 ports on it you could tie into and the throttle body will have at least one and probably 3 ports off the back that will all work for a map sensor.
The ports I refer to are the ones that don't "see" vacuum until the throttle is cracked. They were used on emission carbs to keep timing retarded until the throttle opened a certain degree They were ported ABOVE the throttle blade with a slotted opening that was further exposed with more throttle opening.
A MAP sensor must see full manifold vacuum to function right.
I stand by my statement as far as the definition of a timed spark port, which I defined above.
Thanks a lot to both of you! I have it connected to full manifold vacuum so I should be good. My starting issue must be something else and I'll keep looking. Thanks again!!
01-05-2019, 02:49 PM
Anyone have Holley 4150 style TB with GM ECU? 
