Saturday, July 25, 2009

More EGR Investigation

After following the troubleshooting steps in the manual, I see the two ported vacuum thermal switches are bad. The full manifold vacuum that goes into one port is getting sent all the way back up the chain to the ported vac connection on the carb, screwing up pretty much everything. I can get new ones easily, about $35 each. In the meantime, I have plugged the manifold vac hose which seems to only affect the thermac door on the aircleaner.

Tuesday, July 21, 2009

EGR Issue

I'm having an issue with my '76 regarding the EGR valve operation. The old valve was weak, so was letting exhaust gas pass even with no vac signal. I replaced it with a new valve and it turns out the real problem is that it is getting a vac signal even at idle, so the idle is real rough when the hose is connected. I went all the way back to the carb and it seems the ported vacuum point on the carb body has vacuum at idle too, so the various temp switches are just passing it on. Ported vacuum should be zero at idle, right? Is the Q-Jet due for a rebuild then?