Hi guys and gals,

Here's a picture of a wire that screws into the base of the EGR valve on my '89 TPI setup. But, what does it do? You can see there's a wire that screws into the large metal part, and then this screws into the EGR valve base.

Anyone got clues?

 

its a temp switch for the EGR. Click on the this EGR Temp Switch

 

Oh cool, thanks for that bit of info. Do you know if these things tend to fail or are they quite reliable? I'm rebuilding a TPI engine so now would be a good time to replace it if they're known to be faulty

 

Couldn't answer that one bro. I am just converting to TPI from carb. I bought a new one to be on the safe side though.

 

Reckon I might do the same. They can't be expensive things.

 

FYI
The last time I priced one at AutoZone it was a WELlS EDS4 $49.95+tax.

There's a strip of curved bi-metal inside the sensor mounted to the base that screws into the EGR.
The bi-metal strip expands with temperature. The expansion is stop by the the point of the screw connected to the wire bringing the ECM EGR signal to ground telling it that's it's OK to apply EGR if needed.

The bi-metal strip and screw should be calibrated to make contact when the engine reachs normal operating temperature (approx. 160°F.)

The bi-metal strip is of the type used in old toasters to release the pop-up mechanism. Over time the rate of expansion changes, and it take more time for it to release and the settings has to be adjusted according.

Over time the EGR sensor will stop making contact and the ECM will not apply the EGR when needed, and the sensor will need recalibrating. Adjustment screw should be sealed with thread locker.

 

Last week I foud that my wire had pulled off of the sensor. Fearing drivability issues, I went to Advance Auto and they did not have one on record for our cars. After doing some research, I found GP Sorensen part #: 779-301 is the correct part number for it. $20 bucks, and it works for me. The plug for it is burried in the passenger-side of the engines wiring harness back by the distributor. Be carefull not to break the plastic tab that holds the sensor to the wire back there. Hope this helps.

 

I'm not going to agree with any of that The purpose of the switch is a feedback loop for MAF systems to tell the ecm that the EGR valve is opening and closing properly - NOT to indicate when it's "OK to apply EGR" and open the valve. In MAP - the MAP will see a change in pressure as the valve is opened and shut. In MAF cars the tempature of the valve will change, if it does not change in congruence with the signaling for the valve to open and shut, the there is an emissions system failure, and that is the purpose of the switch.

 

Wow, $49 at AutoZone for an aftermarket unit? The GM unit is quite a bit cheaper. We carry it for $15.

 

 

Anyone have the GM part number?

 

So a signal voltage is applyed to it and when the temp is reached it GRD's it out?