Which is why I said in post # 2 ,to check the temp switch in order to determine if was a real or " imagined " EGR valve fault.

 

Is there a way to test the solenoid (check voltage or resistance etc..) on my 91? My EGR valve appears to be fairly new but that doesn't necessarily mean its not bad..

 

How exactly do I test the egr temp switch? I read that chart but I'm not sure what it means to ground the egr to test it for the voltage. I am great at reading some of those charts and other not so much

 

Connect to battery negative,
usually achieved by " grounding " as in making contact with the engine metal
which is exactly the same effect as running a wire all the way to the batt Neg terminal.

 

I gave the resistance in post #20: 28 ohms.

In my opinion the best way to test the EGR solenoid is to disconnect the connector, connect ALDL terminals A & B and unplug the cooling fan relay (so you can hear what's happening). Turn on the ignition (don't start the engine). Now take the connector and push it into the EGR solenoid just enough that it makes electrical contact. As you move it in and out you will hear the EGR solenoid click (if it's good, of course). I just did this and found that the IAC clicks continuously with A & B connected because the ECM is trying to force it to the closed position. I never heard this before because I never unplugged the cooling fan in the past.

Disconnect the vacuum line that goes to the EGR valve and apply vacuum with a Mity-Vac or similar tool with a vacuum gauge. The vacuum should hold and not drop.

Testing the vacuum valve part of the EGR solenoid? Hmmm. I'm not sure about that one. Just applying vacuum to the throttle body side may or may not prove anything. if the EGR solenoid valve never opens the vacuum will hold. If the EGR solenoid valve opens and the EGR valve is good then you get the same result, so ??? i guess you could apply vacuum and then disconnect the EGR valve. If the EGR solenoid valve is open then you'll lose vacuum, which means it's good.

I just did all of the above and found no problems on my car. So the next question is: how to test the EGR temperature switch? The first possibility I have considered is to attach the leads of a voltmeter to the switch and tape the meter to the windshield. It should read 12 volts when the switch is open and 0 volts when it closes. Method 2 is to connect an LED or continuity light. Lit when open, off when closed. Of course datalogging software will tell you the status of the EGR switch.

Here's a link to an interesting article on testing and adjusting an EGR temperature switch:

http://chevythunder.com/fuel%20injec...temp%20sw..htm

 

The vacuum test will Not work on an 89 EGR valve.

The 89 uses a Positive Back pressure EGR valve and will not hold vacuum with a hand pump. The positive back pressure egr valve needs exhaust back pressure to operate.