I have a 1988 NA that did not pass smog check due to a failed EGR system functional test. I have tested the whole system myself and don't understand why it fails. The book test is to apply vacuum manually to the EGR valve, which is supposed to decrease idle or make it stall. I applied manifold vacuum to the EGR and got a slight increase in idle (leaning effect!?).

Vacuum source is good at 15+", and remains so all the way thru to the EGR nipple (when EGR solenoid valve is actuated). EGR diagraph does leak slightly, but vacuum only drops to 11", plenty to open the valve (I checked and confirm air flow thru the EGR valve itself down to only 3" of vacuum!).

Could the passages routing exhaust gas to the intake thru the housing itself be blocked? What path do these passages take?
Are there any other systems that impact the gas recirculation part of the EGR system??

 

That is very possible. When I took mine off it was totally caked with carbon deposits.

 

For a non turbo:

If you ever removed the exaust manifold, you'd see a single hole of approx 1/2" diameter in the maniflod, that mates with a hole on the bottom of one of the rotor housings. The rear rotor housing if I remember right.

That hole in the exaust manifold feeds air to the 1/2 inch hole on the rotor housing and from there the exaust gas goes up a passage internal to the intermediate housing and exits at the top of the intermediate housing. That exit hole is under the EGR valve itself. It then enters the EGR and IF the diaphram is sucked up, ports that air into another passage in the intermediate housing that goes to an internal passage that leads to the intake ports of the intermediate housing.

If there is no suction on the EGR from the solenoid, then the two passages mentioned above are blocked off from each other and no exaust gas goes to the intake.

EGR diaphrams should not leak. Remove yours and put some suction on the EGR to see if the diaphram will open and stay open. Not a big deal.

I've not a clue how Calif checks this valve. In Tx I pass the rollng emissions with non functioning EGR valves. They seem to have zippity to contribute to the emissions reduction in my humble opinion. Note how the later versions do NOT have a EGR at all.

That describes a non turbo. The turbo route is very much different.

 

Thanks for the description of the passages; makes perfect sense to me now. A previously none functioning EGR valve may have allowed exhaust deposits to build up, ultimately blocking the passageway. I will pull the EGR valve (AGAIN), and probably the exhaust manifold, to see if I can clean out the passage.

I had the kind of problem with a Toyota years ago; I cleared out the passage and it passed the smog test, but then it ran worse, so I disabled it.

 

I don't mean to hijack but I'm trying to complete the assy of my 3rd gen reman and noticed it has a tapped hole in the top of the intermediate housing thatmy old engine didn't have. Is this a 2nd gen housing and is this the port referred to for the EGR? Would appreciate any suggestion as to what I should do; seal it? how? Thanks.

 

The EGR on a NON TURBO series FOUR sits on three holes. One large hole is fed exaust fumes from a half inch hole below the exaust port on the rear rotor housing. There should be a hole on the exaust manifold that mates with that hole below the rear rotor housings exaust port. The hole in the exaust manifold has a tube that reaches about four inches into the exaust manifold to caputure the fumes.

Just look at a non turbo exaust manifold gasket and notice the small half inch hole below the rear exaust port.

ANyway, when the EGR gets the vacuum input signal the diaphram inside the EGR opens and makes a passage b/t the LARGE hole and the two small ones to feed exaust fumes to the intake ports on the Intermediate housing.

 

Turns out it was the exhaust manifold gasket installed wrong, therefore blocking the EGR system exhaust port. Wonder how the previous owner got it smogged