P0400 trouble code EGR malfunction

While swapping out the EGR due to throwing a P0400 I discovered there is a difference between the EGRs on 94/95 (7ga) and the 98 (7gb). The early 7g had a wire connector on them ending in a plug that connected to another plug located between the valve cover and body of the intake manifold. Anyone know if the early version EGR can be used on the later 7g by just ignoring the electric plug? Also can someone explain how to determine if the problem is the EGR, the valve that connects to the EGR via the air hose, or how to trouble this system. The EGR is clean inside and the internal rod moves (opens) under suction.

you can use 7ga EGR valve, just cut of the wires to the sensor. Thats a temp sensor that tells the ecu if the EGR works or not. On OBD2 systems, thats sensor is missing because the MDP sensor on top of the Intake manifold does that. When the EGR opens the MDP sensor senses the dropped pressure or the extra airflow (whatever you wanna call it) and sends the signal to the ECU.

The entire EGR system has three components - valve, check valve/canister and solenoid. The only thing the ECU does is to apply 12V at the solenoid when it feels that the EGR valve must be open and then get the feedback from MDP sensor.

Troubleshooting.

1. Vacuum lines - there are many of them, make sure they are all good.
2. Electrical - now this one is tricky because you cant trip the ECU to open the EGR unless under specific driving conditions. They only way to know that the solenoid is getting 12V, is to tap the wires and extend it to the cabin and look at the voltmeter when the ECU activates it. Read below about the OBD2 scanner method.
3. Solenoid - follow back the vacuum line from EGR valve to canister (little round thing in brown/red color) and from canister to solenoid (to find out which one it is). Disconnect plug and then apply 12v to the pins of solenoid (use alligator clips or another plug from J/Y vehicle). With the car running check for vacuum before solenoid, after solenoid and after canister. If there's no vacuum before solenoid then the passages in TB are clogged - remove TB and clean it. If vacuum is present before solenoid, but there isnt after it, then the solenoid is bad. If vacuum is present after solenoid, but nothing after canister then the canister is bad.

Fancier OBD2 scanners can activate EGR solenoid and it would help if you have access to one of them. I dont remember if EvoScan can do that. If not then do it the old fashion way that I described.

4. Clogged Intake manifold or exhaust passage - the EGR bypasses exhaust gas from cyl.4 to intake manifold. The passage from cyl.4 is very small in diameter and could get clogged over time. Remove EGR valve, plug the left hole on the intake manifold (I usually stick my finger in there) and have someone start the car. If exhaust pours out of the other hole (dont be scared cuz it feels like heavy sputtering) then it most likely has exhaust flow, but maybe not enough. The clog usually occurs in the Intake manifold or right where the gasket is, between the IM and head. Now this is where you take the IM out and you clean it and inspect the passage in the head. I poke it with a coat hanger wire and just drive it back and forth and spray some brake cleaner until I like it.

ERG hole that gets clogged. Clean if there's no exhaust flow

http://i1006.photobucket.com/albums/...ps630406b6.jpg

Right hole goes to the head, left hole to the plenum. Plug the left hole and start the car to check for exhaust flow from right hole

http://i1006.photobucket.com/albums/...psea0991f3.jpg



Hope that helps