Being in the process of trying (way too hard btw) to switch to an Edelbrock baseplate/runners on my late '86, I've run across a problem. I was going to be a good doobie and put back the EGR, but I found it doesn't fit under the plenum with this setup!

Since I don't feel like yanking the now-modified and unreturnable hardware, I decided to eliminate the thing, especially considering how hard it is to get at for replacement. Of course, I found the 'diode trick' on various forums and was ready to go with that (yes, I do plan to reprogram my eprom in the future).

Then I found a post elsewhere that told me '85 thru '89s used ported vacuum (to keep the EGR closed at idle) with a NO (normally open) vacuum solenoid. The diode trick, if I understand correctly, shorts the temperature switch wire to the ECM ground signal that controls the EGR vacuum solenoid through a diode. Since the parts were sitting around loose, I decided to check who's normally open and who's not. Sure enough, my solenoid is open (passes air between its 2 hoses) when sitting unconnected. When I apply a 9v battery to it, the solenoid can be heard to snap on and the opening between the ports is closed.

So I checked my EGR valve. It opens when vacuum is applied, and is closed when not.

This means that the ECM is actually disabling the EGR when ground is applied to the solenoid. Seems to me that this kills the diode trick, which wants to ground the temperature switch wire when the EGR is open (enabled). In other words, the trick seems to rely on the ground signal enabling the EGR, not disabling it.

Do I have that right?

 

I think you are making this harder than it needs to be. Just get an egr block off plate and you will be good to go.