kylew707

1997 z28, h/c, bolt ons. Anyways, my car has been fuel fouling the plugs within 10-15 minutes. I got a live data scanner on it and everything looked good except the coolant temp and air intake temp were both reading -40. I've had a bad temp sensor before but it threw a code, ran like crap, was hard to start when warm etc. so I'm familiar with what a bad one can cause. I'm stumped with it this time though. It's not doing any of those things. Idles fine, revs fine, starts up fine every time, no codes. The only thing its doing is fouling the plugs. I traced the wires and found they were a little frayed at the pigtail. Fixed them and still reading -40. I put a new sensor in it and its still -40. I traced the wires as far back as I could and they look fine. Any idea what else would be causing it to still read -40? The only other thing I can think of is, there isn't any coolant or water in the car right now. Would that make a good sensor default to -40 if it didn't have coolant to read? I would assume a working sensor would read zero or even higher based on engine heat regardless on coolant flowing or not?

shoebox

The sensor will read whatever temp it is exposed to, whether in coolant or not.

Time to get out the meter.

kylew707

Unfortunately. I hate electrical problems. I didn't check the IAT sensor or wiring. If that were faulty, maybe it's causing a false reading for the sensor too? They are both reading -40

Injuneer

Fouling the plugs means it's running rich. A false low coolant temp puts the PCM in cold start enrichment mode, and richens the A/F ratio. A false low coolant temp would also prevent the PCM from going into closed loop, which means the O2 sensor feedback cannot be used by the PCM to correct the excessively rich condition.

Reading the code details in the factory manual, the codes for low IAT and CLT set when the temp indicates BELOW -40*F.

You have to face your electrical demon

kylew707

Yeah when I initially had the scanner on it, it never went into closed loop and I let it get close to 210 according to the cluster gauge. I do have a maf code, po100, but the plugs were fouling even before that code came up.

Injuneer

P0100 is not unusual for the 97 models. The problem is often a break internal to the harness of the pink wire that supplies 12V to the MAF sensor. Key on, check for 12V between the pink wire and the black/white wire in the harness connector.

Shoebox's temperature sensor guide is very easy to use.