lathens

Did plugs last weekend; found six of them fouled! Also installed a new coolant temp sensor and pigtail (one in waterpump). I had to add about an extra foot of wire to the pigtail.
I remember now what happened. Car was in storage at a friend's house for several years. He started it and drove it once a month or so. I just got it back from him about 9 months ago. Apparently the temp sensor wiring must have gotten caught by the fans and ripped out. Anyhow, car ran fine all winter with no problems until the weather got warm. Car always ran so cool it stayed in closed loop. Once hot weather arrived, car started running like crap and dumping fuel after it heated to open-loop temp. Now that new sensor is installed, car runs like crap and dumps fuel when cold until it gets in open-loop. I think its running rich even in open-loop because gas mileage is about 10 mpg. Was getting 17 mpg in the cooler months. I took it to azone and had it scanned; no codes. I need to find what is wrong before I foul more plugs; don't want to do that! Have to pull headers to replace plugs and my 16 y/o son is burnt out on working on the car with me. Any ideas please?

lathens

oh, btw, when i did plugs last weekend all 4 on the passenger side were black and sooty whereas only two on the driver's side were.

Injuneer

With the open CLT temp sensor circuit showing infinite resistance, the PCM thought the temperature was -40*F. It set very low A/F ratio (= very rich, ~4:1) for very cold start and never leaned it out because it never saw the engine warm up. Somewhat OK in very cold weather, serious problem in hot weather. PCM will not go into closed loop until CLT reaches ~120*F. Should have set a code, but if it was just short trips, might not have picked up the open circuit.

lathens

Oh, sorry...used "open loop" and "closed loop" terminology wrong. I guess closed loop is above 120F. So, what should I check now since it is still running rich? Any OBDII data logging software and cables available anywhere? I use to have Autotap but lost it in divorce and moving.

Injuneer

Have you verified that the PCM is reading the CLT sensor correctly. Scanner should read it. Any excessive resistance in your extension can throw the readings off.

I used to use Autotap on my newer GM vehicles. Have no idea what else is out there now. A quick search seems to turn up several low cost units that plug directly into the ALDL connector. Have no idea how good they are.

lathens

I was thinking the same thing about the resistance. I made my extension as short as possible but still able to reach the sensor and used 18ga wire. I'm not certain how long the original stock length was.

Injuneer

The quality of the connections is more important than the length of wire. Did 18 ga match the existing wire? Seems too light.