I have an 89 iroc that i have recently pulled out the 305 and put in a 350. I now have to pass smog. The problem that I face is i keep failin on NOX. From what i have read and learned is that NOX is a byproduct of high cylinder combustion temperature due to a lean condition. So far i have put on a to try to pass smog a new catco high flow cat, new egr, chip that goes with a 5.7, a new set of 24# injectors, holley AFPR, o2 sensor. Well my car has been in the shop for the last 6 weeks and I really want to wrap this up any ideas on what could be wrong? any help would be nice. thanks, justin

 

First I would check for vacuum leaks. Get a can of carb cleaner and spray all around the manifold connections if it leaks the engine should speed up. Lean means more air less fuel. If you didn't change the chip to read 24# injectors it should be rich.
Make sure your timing is on and accurate (6 degrees with connector undone).

 

thank for the input but there are no leaks. the arrival we've come to today is pointing to something is wrong with the diverter valve or something is wronge with the ECM causing the valve to malfunction.__ If this repley is from the DON that has the shop up near the pond you may be seeing my car soon if this does not get handled in the next week or so. Any further addvice would be helpful. justin