Hey all.. I just recently got my hands on an '87 T-Type. Was having problems with knock at ~10-12lbs boost, and it turns out the spring keeping my EGR closed was old and worn, and was opening when the turbo kicked in. (Discovered this because a friend with a GN had just fought with knock in that range for a few -months- and that was his problem, too.) Well, from what I hear it's a common problem..and the solution to this point is either block it off with a plate or get a new EGR valve. I think I've come up with a better solution. I'm gonna go into the logic behind the statement so someone out there can prove me wrong..if I am.
Facts (as I know them):
1. EGR is closed under boost.
2. EGR vacuum to open the valve comes from intake vacuum.
Right? I'm hoping so..because my theory relies on that. I came upon the idea by accident, actually.. A friend had an EGR valve on his Firebird, but no solenoid, control lines, etc..and the hose nipple was capped off, from factory for all I could tell. His valve was -stiff-. I got to thinking, 'if I capped it off the same, would mine be that stiff?...what if I put pressure behind it? That'd hold it closed pretty well I'd hope..'
So here's what I did. (Yes, I did this to my car, driving it like that for two days..problem fixed, EGR functions normally for all I can tell.)
I took the boost line that plugs onto the wastegate solenoid, and put a T in it..on the new section of line, I put in a check valve allowing flow only when there was boost. Then I put a T between the EGR valve and EGR solenoid...hook the valved boost line to the new EGR T.
When the turbo kicks in, starts pounding out 12lbs of boost and would normally force the EGR open, the new vacuum line with check valve would put the same 12lbs behind the EGR valve to keep it closed.(Which, granted, may not be enough to keep it closed 100%, but it's proven effective so far.) When I hit cruise and the EGR opens up, the vacuum provided to the solenoid will open the EGR valve itself up without causing problems by creating a vacuum in the intake system (The check valve won't stop a vacuum on -that- side, if I were to put a check valve in the other way it would make this idea totally void.) because that's where the EGR's source vacuum comes from..BUT..the check valve stops it from opening the EGR with vacuum present on the boost line during cruise/idle..
Anyone follow that at ALL? Anyone out there who can approve/disprove my theory here?
Oh, PS, parts required to make this modification:
Two vacuum T's, one check valve, and 2.5' or so of vacuum line. I also needed two vacuum size adaptors, though the T's were both of the same size line.. BUT I have a feeling those weren't stock lines, so your mileage may vary there.
I actually got away with one T and a combo T/check valve/size adaptor I stole off a Buick LaSabre one of my friends was selling for parts. No part numbers, sorry.