Originally Posted by showgun
I recently purchased a 90 K5 blazer with a tbi 350. I have been having combustion issues and had no luck with basic timing advance/retarding adjustment and plug change. I removed the drivers side valve cover today and they are 062 vortec heads.
- Correct me if im wrong but I need to have the computer adjusted to run the TBI differently right?
Also, The rocker arms are not perfectly aligned on the valve springs. They tend to sit off to the side of the rocker. When I get time I'm going to check torque on them, I can move them one side to the other by hand. The only top end I've been into in the past 10 years is my cummins. Any info will be appreciated.
The computer will take control of the base advance as soon as the engine fires and will counteract any changes you made electronically.
What exactly are the issues and symptoms?
Changes to the TBI operation take reprogramming the computer. If the heads have been changed the question needs to be asked about the cam. GM's TBI is a speed density, manifold absolute pressure system. It is very sensitive to the realtionship of RPM to throttle blade position to manifold vacuum (absolute pressure). Changes, especially to the camshaft, greatly upset the mapped relationships the computer is looking for. The Vortec heads allow more air to move through the engine mostly in RPMs above 3000 which is about the effective limit of the original Swirl Port heads. So these can get into a situation even with the original cam where the air flow exceeds what the program expects for the originally programmed relationships. Changes to 1.6 rockers, the addition of headers and duals, the deletion of EGR or its malfunction can also lead down this road.