Running Rich?

[popeyesteve]

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 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.

[Gunslinger]

Most, if not all, systems won't go into closed loop until the engine reaches a preset temperature. Whether it's 195 degrees for you I don't know, but they will run rich until warmed up to that predetermined temp.

I can't tell you whether it won't store codes until at a particular temperature...I simply don't know, but it doesn't seem that it would be so limited. It is a different system from the current OBD II and primitive by comparison.

You could have a bad connection somewhere which is fooling the computer, a bad O2 sensor, a problem with the computer itself or who knows what.

Your problem may be as simple as the carburetor needing adjusting due to the decreased back pressure from the converter being removed and having freer flowing dual exhaust installed. That computer controlled carburetor was somewhat of a marvel at the time, but is now thirty years old and not too many techs know how to deal with it. You may need to find a good, experienced carb guy to look into it.

[Avanti83]

Steve

Before we go any farther, Did the previous owner put a oxygen sensor back into the exhaust system when he changed it?

As for the temperature issue, 180 thermostat should be fine for your system but if it's bad it will lead to your problem. Had the same problem with a friends Firebird of the same era. Thermostat was not closing and the engine would not get warm enough. A new one solved the problem. It's not that bad to change.

Bob

Edited June 12, 2012 by Avanti83

[popeyesteve]

The O2 senser is intact and hooked up. The air pump is just just venting to atmosphere, since the cat is missing, but the "system" has no way of knowing that. The fuel metering solenoid is cycling as soon as the key is turned on. Everything seems normal except the rich condition and the TCC lock-up thing. I am getting differing opinions on whether the temperature thing is a player or not. Wish I had a definate answer one way or the other...

[WayneC]

Most, if not all, systems won't go into closed loop until the engine reaches a preset temperature. Whether it's 195 degrees for you I don't know, but they will run rich until warmed up to that predetermined temp.

I'm not familiar with this particular application, but the computer needs input as to engine coolant temperature, so it's also possible there's a coolant sensor giving bad (low) readings. Check to see if there is a coolant temperature sensor (likely on the thermostat housing) and that it has intact connecting wires at both ends of the harness. I wasn't able to find info on how to test the sensor against specs, other than this general article:

http://www.wellsve.com/sft503/Counterpoint2_2.pdf

My next culprit suspect would be a bad exhaust oxygen sensor.

[popeyesteve]

The car sprang a radiator leak (lousey old repair) last year, so I had it recored. While I was at it, I replaced the water pump, fuel pump all of the hoses and belts. I discovered then that the coolant sensor in the thermostat housing was broken off and just functioning as a plug (more of that PO stuff) with the connector just laying loose. I put a new sensor in it at that time. Later I realised that the PO had also removed the bulb from the check engine light (I guess so he wouldn't have to see it "on" all of the time). I put a bulb in it and it seems to function as one would expect if no faults are stored, on with the ignition and goes off after engine start. I have not done any ohm checks yet.

[CaffeineRacer]

I know this is an old thread, but I'm going to give some answers in case anyone else has a similar problem. Numbers refer to the OP original question list.

1. Yes if you run a 180 or cooler thermostat the computer will never go into closed loop and stay in its "full rich, limp home" mode. The thermostat is the culprit here. Buy a new 195 degree thermostat and you'll be all good.

2. When you turn the ignition key to "on" the check engine light is supposed to come on to let you know it's working. Then once the engine is running it will turn off, unless of course there are any fault codes. In this case there were no fault codes which is why the CEL would turn off. Again the problem was improper engine operating temperatures.

3. Yes, CCC cars are programmed such that the torque converter clutch (TCC) will not engage unless the car is up to operating temperatures. This is to pretty the engine from lugging too much while cold.

Hope this helps someone in the future. The thermostat thing is a common issue with these systems that people over look. Also best way to tell you engine is going into closed loop is to connect up a dwell meter in 6 cycle mode to the bright green MCS lead (passenger side engine bay wall) and measure the dwell. If it is fluctuating then your in closed loop (varies between 10-50ish). If the meter is fixed (probably around 30) then you're still in open loop.

[chuck]

Another problem with Quadrajets, electronic or not, is gas soaked floats. They get heavy after years of sitting in gas and then the gas level in the bowl goes up and you get rich operation. The electronic system doesn't have sufficient range to deal with this-it happened to my 82 Avanti.

chuck

ARB-3553

[chuck]

Make that RQB-3553

[IndyJimW]

Here is a site that may help.

http://performanceolds307.tripod.com/id1.html

Jim Wood