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Discussion Starter #1
Okay, while I am waiting for my new radiator to show up for my '87 El Camino so I can get it back on the road, I'm trying to figure out a problem with my 1982 Avanti II. It has the stock LG4 305 with electronic Q-Jet and 200R4, same as the Camaro, El Camino, etc. for that year. It has all of the emission equipment installed and hooked up, except the previous owner took off the cat converter and put on true dual exhaust. It starts up and runs just fine when cold, but never seems to come off open loop operation even after it is driven, because after it is warmed up, it runs very rich, belching some black soot and loading up (trying to flood) especially at idle and the gas mileage sucks. The check engine light comes on with the key, but goes off as soon as the engine starts, so it doesn't seem to be storing any codes. They did a fine job of hiding the ALDL plug in this car...I haven't found it yet. On my El Camino (when it was still stock) the TCC would not engage until the engine reached operating temperature (the thermostat opens) and this Avanti's TCC rarely engages. It also rarely gets to over 180-185 degrees, so it may have a 180 degree thermostat. So here are my questions.

1. Will this system never go into closed loop until the temperature is up to 195 degrees?
2. Would it never store an error code until it reaches 195 degrees and then senses a fault?
3. Is it normal for the TCC to remain disengaged until the operating temperature is up to some minimum per the factory programming parameters?

I know that I could just go get a 195 degree thermostat, but it is underneath a bunch of stuff and I don't want to bother with the mess if it will do nothing to help the problem.
 

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Well, I'll give you some thoughts. I'll bet that when the exhaust was changed to true duals all the O2 sensors were ditched too (won't speculate why...). So, are the O2 sensors still installed? Might be both before and after the (original) cat convertor but at least before. If gone it will never run in closed loop regardless of temp of coolant. The CEL may not be on (in dash with engine running) but codes can be triggered in the ECU so you need to find out how to pull the codes. Whatever thermostat is called for from factory must be used as the whole system is calibrated as, well, as system. So, that's my first guess, O2 sensor missing or not connected. Hope this helps and good luck!
 

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0pen loop

The last post is correct. Also there is only one o2 sen. before the cat. 180 therm. is okay my car runs one. The conv. lockup should work when cold after about 40 mph. Is the plug still in the harness for the 02.
 

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Discussion Starter #4
The O2 senser is intact. The air pump outlet to the (non-existant) cat converter is venting to atmosphere so the "system" doesn't know the cat is missing. Since the check engine light comes on before the engine starts and goes out afterward , I have to assume that it is not setting a fault code.
 

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If the PO installed headers with the true duals, then the O2 sensor may not be getting hot enough. Most of us with headers have gone to a heated O2 sensor to solve this problem. You can measure the output of the O2 sensor with a DVM. Baseline is about .5 volts. If you increase RPM's to about 2000 and hold them there, you might see the voltage start to swing wildly from about .7 down to .3. If it is moving back and forth like this, it is providing the Closed Loop info. If it remains steady, it is either faulty, or is so far downstream in the exhaust that it can't get hot enough to operate.

By the way, my first restoration was a '63 Avanti r2. Loved it- wish I still had it.
 

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they go into closed loop between 130 and 180.the factory thermostat is 195.but if its at 185 or so it should be in closed loop unless there is a problem with your coolant sensor or wireing. my 86 would go into closed loop about an 1/8 in. over the 100 mark,you could hear it when warming up as it changed.you could have a faulty ecm. does the solenoid in the carb tick as it idles ? make sure the ecm has its fuses intact there should be 2 10 amp fuses for the ecm. you need to find the aldl connector to see if the ecm is even operating before you throw any parts at it.that way you are not chaseing your tail
 

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Discussion Starter #7
The coolant (temperature) sensor is new. The gauge has a separate pick-up. The mixture control solenoid starts cycling as soon as the key is turned on. The car has stock cast iron exhaust manifolds and the O2 senser is in the pipe just below the manifold. If this thing has a standard ALDL plug, I haven't been able to find it. There is a more standard looking 5-pin plug connecter under the dash that may be a precursor to the ALDL system (Avanti bought drive trains from GM as needed, so it COULD be a 1981 or 1982 system, who knows) but I am not sure what it is exactly. I will check the fuses tomorrow...
 
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