1G Error code 43 DTC EGR CEL

[Auto RS T]

I'm working on a 94 Talon AWD. My neighbor asked me to look at it because the CEL came on. He said it seems to run and drive fine. Pulled a Code 43 (EGR) from the DLC with a voltmeter. Knowing this car should have a Federal ECU I pulled it out of curiosity. Found MD304484 a 94 Federal M/T ECU with an EB21 EPROM, no noticable modifications. After searching, to my understanding. I found that if resistor R129 is not installed, the ECU will have the ability to throw this code. Simple fix. Block the EGR, cap the lines, and solder in the resistor.

http://www.dsmtuners.com/forums/problem-diagnosis/235003-cel-43-egr-help.html?highlight=CEL+43

http://www.dsmtuners.com/forums/bolt-tech/152101-code-43-egr.html?highlight=code+43

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Now. I actually want to repair the EGR system. How does the ECU call for Code 43? How does it determine the EGR fault basically? I know it uses the temp probe, but I don't know what the ECU looks for to set the code. Does anyone know the conditions to set Code 43?

After removing the EGR it did seem to be sealing. There wasn't any carbon that went to the outside edge or between chambers on the flanges. Carbon buildup wasn't bad overall, but I will pick and clean it out tomorrow from the intake and the valve anyway.

Suspects for testing after a vac line check are: the EGR Valve, EGR Temp Sensor, Thermo Vac. Valve, and the EGR solenoid.

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Curious about the fault trigger for now, it will help me know if I have fixed the problem without guessing how long it will take for the CEL to come back on.

 

[Auto RS T]

First off. After inspection, this vehicle is not equipped with an EGR Solenoid so I will not be testing this. Onto the rest.

Testing the EGR Valve.

To test the EGR valve, plug the bottom port and connect a hand vacuum pump to the top port. Pull 19.8 in. Hg of vacuum. Vacuum should hold. You will notice the pintle pull out from the orfice. Observe to see if the pintle hesitates or sticks when pumping. The travel should be smooth. Now pull 8.5 in Hg of vacuum and blow through one of the chambers. Air should travel from one camber and out the other. Here's the setup, the tee is capped on the end you can't see.

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Pintle Closed

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Pintle at full travel 20 in HG of vacuum

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Results: Before I cleaned the EGR valve I tested it. When I first began to pump I noticed the pintle stuck and then "popped" open. After noticing that, vacuum was retained at 19.8 in Hg. Then I pulled 8.5 in Hg of vacuum and blew through the chamber, air passed, meaning the orfice wasn't clogged and the diaphram is in good condition. This told me the valve was functional, but needed to be cleaned. I took a small flat srewdriver and picked out the carbon deposits, both from the intake manifold (being sure to pull the deposits out and not into the manifold) and the EGR chambers. I payed extra attention to the pintle and removed all the black soot from it using a fine wire pipe cleaner and carb cleaner. Retested and it worked flawlessly. Reinstalled EGR Valve with the gasket.

Testing the EGR Temp Sensor:

Set the tip of the temp probe in some water. Hook a multimeter to the ends of the electrical connector and set it to ohms. Heat the water and watch the resistance.
@ 122*F it should read 60-83 kilo-ohms @ 212*F it should read 11-14 kilo-ohms. The resistance will raise and lower with the temp of the water steadily. Here's the setup for testing. Ignore the reading on the multi meter, the probes aren't making contact in the pic.

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Results: The temp probe seemed to operate efficiently and accurately. Here's the specs122* I had 67.2 kilo-ohms @212* I had 13.23 kilo-ohms. The sensor operaton looked smooth between these values changing steadily. Diagnosis is I have a good EGR Temp Sensor. Reinstalled.

Testing the Thermo Valve:

Apply vacuum to the valve and check for air movement between the ports. You can do this by putting your finger on the opposite port and feeling the suction. @122*F or less the valve should leak vacuum, @176*F or more the vacuum should hold. Here's the setup for testing the Thermo Valve.

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Results: The thermo valve leaked vacuum at 122*F and under. It also leaked vacuum over 176*F all the way up to the tested 212*F. We have a bad thermo valve.

Ok we had a formerly sticking EGR Valve and a bad Thermo Valve. I will test the new thermo valve before I install it. Any help on my question in post #1 regarding the conditions to set Code 43? I know that having the temp sensor circuit broken will turn the CEL on. What else?

 

[Auto RS T]

I called Napa to get a Thermo valve and they don't list it as available. Then I tried the dealer, they want $60 for the valve. Wow! So I searched through my spare parts and found two more Thermo valves. One wouldn't even hold vacuum if I plugged the opposite port, meaning it wasn't even worth testing. Luckily the other tested good and held vacuum over 176*F.

Reinstalled the Thermo Valve and topped off the coolant. Car fired right up smoothly with no CEL. Now, since I still don't know the conditions to set Code 43 I will be driving the car for a few days, if I don't return to the thread, problem fixed. However, if I do find the conditions to set Code 43, I will post them up.