My Dad drives a well-maintained 1996 Z28. Modifications are minimal and include a K & N FIPK, a Stainless Works Y-pipe with cats, and a Magnaflow cat-back system.
The car has had recurring problems with the SES light coming on under various conditions, and the code indicates an EGR problem. Both the EGR valve and solenoid have been replaced, with the valve being replaced a number of times since this problem first appeared. Yet the light won't stay off.

The car runs extremely well, and the when the light comes back on (my poor Dad has to clear it regularly) there's no detectable change in the car's performance.

I've seen the information on the LT1 EGR system on ShoeBox's website. Is it possible that my Dad's exhaust upgrades are causing this problem? What is the solution? Is a custom tune required?

Thanks very much for any help,
Rick

 

Is it the code for low flow (P0400) or theone for the solenoid electrical circuit (P0403)?

Assuming its P0400 - Low back pressure exhausts cause problems with the EGR flow. Your dad's doesn't seem all that free flowing, with no headers and with cats. I've heard rumors of there being a "low back pressure" valve available, but I don't know if that's true. Its also possible there is carbon buildup in the EGR path.... at the manifold, in the tube or in the manifold where the tube connects or where the EGR pintle enters.

Also make sure there are no cracks or leaks in the vacuum lines.

There are always the options of defeating the code in the PCM, or using an external spoof circuit.