another day, another code...

[Paul Workman]

Originally Posted by Kevin

my understanding is that the engine produces enough vacuum to keep the secondaries running under WOT and it's only when you start playing around at part, or full throttle in a high gear and low RPM that you need the extra vacuum to keep thing running. either way this requires pulling the plenum which I'm not comfortable doing.

Well, actually you're partially right. The engine provides vacuum most of the time, except during WOT. At WOT the vacuum drops to near zero, and the reservoir only pops the actuators open. But, then its the pump's job is to keep them open as long as you're standing on the throttle.

Wiring the secondaries open sounds like a good way for you to go, at this point. It is reversible at any time, and it may reveal some other gremlins in the 'lectric chit' by eliminating the secondaries at least.

Far as keeping the secondaries if the car is subject to periodic emissions inspections go, it would give me pause to contradict Marc. However, I am ignorant of any report where emissions would pass, but only if the secondaries were in place. (Furthermore, the next generation LT5 eliminated the dual runners and went with one injector. What does that tell us?)

In my case, my porting included the secondary runners. So reinstalling the system would involve fabricating new (bigger) throttle plates, (NOT gonna happen), OR a custom gasket that closed off the secondary runner and revert to a stock calibration, long enough to pass inspection...

Far as pulling the plenum goes, it is really very simple, for anyone that can walk and chew gum at the same time. You'll need a gasket set from Jerry, and while your at it, you might freshen the O-rings on the fuel rail and the injectors too, if you haven't already.

Make a list of the connections you disconnect for reference later. Drain a few quarts of coolant into a catch can (to be reinstalled after). Then just remove the fuel line block, remove the screws and the PVC line, purge tube, to the TB, the left and right side vacuum connections to the middle of the plenum, and prop the front of the plenum up while you remove the vacuum tube under the TB's "chin" and the two DIS connectors. Then remove the MAP sensor and it's bracket, and un-hook the two connectors at the back of the plenum, the IAC and the TPS and the air temp sensor connectors, and then just roll the plenum over to the drivers side to rest on the wheel well gasket - you don't have to disconnect the throttle cables, unless you are completely removing the plenum for another reason: leave them intact. (However, since it sounds like you're possibly having electrical gremlins, removing the throttle cables to completely remove the plenum to access the electrical connections for inspection and possible cleaning (use a an electrical contact cleaner, and compressed air), might be a good idea.)

Before reinstalling the new plenum gaskets, I lay the gaskets on something flat, like a plywood board, and spray the top (plenum) side with silicone spray. This amounts to a "release agent" which will facilitate the next plenum pull by possibly being able to reuse the gasket once or twice or maybe even 3 times (and counting!) Just make sure both surfaces are absolutely clean; use a utility razor blade or window scraper to get all the little flecks off the two mating surfaces, followed by scrubbing the metal with a rag having been wetted with brake cleaner. (The key is to get the metal absolutely clean, especially of any oil. I prefer the CRC "Brakleen" or one with the tetrachloroethylene/trichloroethylene (red/white can, but NOT the green/white can), i.e., NO residue (read: NO Naptha based crap or gasoline, etc.) to better allow the gasket to adhere to the IH and facilitate future removal of the plenum w/o damaging the gasket.)

And, while you have the plenum off, that would be a good time to remove the two ground lug bolts at the top of the block, in the area under the MAP sensor, and wire-brush the many lugs and the anchoring bolts before reinstalling. Some dielectric grease smeared on the lugs too will retard future corrosion due to exposure to the air and moisture. (It may or may not cure existing electrical problems, but may well head off a couple that were waiting their turn to drive you nuts!)

Good luck!