Hello everyone!

I've got a quick question about the TPI EGR valve.

I've got an "N" type valve on my 85 TPI intake, however, as I was installing my solenoid, I realized that I had put too short of a vac line on it. When I went to pull the line off the solenoid, the solenoid kinda exploded, lol (I had modified the bracket so I could bolt it in under the plenum for a cleaner install) I was able to find all the pieces, but then I realized I had another problem on my hands -- Should the solenoid be normally open or closed? I can set the valve up either way, but I have no idea what the TPI wants it to be.

So, should it be open until the ECM applies the ground, or should it be closed until the ECM applies the ground?

I'd assume it should be closed, but I am not positive, so I figured I should check...

Thanks!

Russ

 

Alright, I did some extensive searching and found my answer. Decided that I'd post it here for anyone else who needs it in the future:

With the 350 TPI engines, the EGR valve uses a 3 ended solenoid. Two ends face out the same way as the electrical connector, and one end faces the other way.

The opposite end simply has a foam filter on it. It is used to vent the EGR valve, letting air in as needed.

On the side with two ends, there is a metal and a plastic pole. The metal one goes to the vaccum port on the bottom driver's side of the throttle body, and the plastic one goes to the EGR valve.

The solenoid is rapidly pulsed (opened and closed quickly) to control how wide the valve is opened, with the pulsing being based on the EGR temp sensor threaded into the base of the valve.

The solenoid is a normally open valve, however, only a small amount of vaccum is applied to it when you are not touching the gas pedal. The vaccum port on the bottom of the throttle body opens up directly under one of the butterfly valves, so when the vehicle is at an idle, with the butterfly valves closed, that vaccum port has very little vaccum, if any. However, as soon as you open the butterflies, the port recieves full manifold vaccum. At the same time, the ECM uses the TPS to see that the butterflies have been opened, and begins plusing the EGR solenoid as required to get the desired temp reading from the EGR temp sensor.

Hopefully my deductions are correct, so that anyone searching in the future can figure out how this works

 

At least on the '88 TPI setup, the "sensor" on the valve is nothing more than a switch used by the ECM to "see" that EGR is working AFTER it commands the solenoid to let EGR into the intake.

That switch is triggered by temp, so when exhaust gas passes, (again after the valve opens) it heats up the switch obviously, (probably goes to ground at whatever the temp is) which the ECM monitors to ensure that EGR has been introduced. It's a simple open/closed kind of switch, like a coolant temp idiot light switch.

I'm not certain this is applicable to all years, just '88.