Hey guys,

I need some advice on how to troubleshoot this. I've done a search but I can't find anything related.

My 1997 trans am is showing a po118 code (engine coolant temperature sensor high voltage). I'm not sure if this is related to mys talling problems - but my car will run fine, smooth, but once it warms up and gets hot, it'll start sputtering. It sputters and starts to die, and when I give it gas to get the revs up, the rpm needle immediately drops and the engine stops firing - goes dead and stalls.

It doesn't start up until I crank it for a good 5-6 seconds while flooring the throttle. Revs slowly go up and I have to keep it in the 3-5k rev range for a couple seconds for the idle to smooth out again. But it'll start stalling out more often until I cool the engine down. When it stalls, it doesn't seem to set a code or anything.

Not sure if the po118 and the stalls are related, but any tips and advice would be appreciated! I changed the opti/waterpump/plugs/wires about 1000 miles ago.

 

If the ECT sensor is faulty, and telling the PCM that the engine temp is colder than it actually is, its going to run rich and stall. At low temps, the PCM increases the A/F ratio to richen the mixture for a cold start. If the engine warms up, and the ECT is still telling the PCM the engine is cold, its going to be running pig rich, and won't go into closed loop.

Extended cranking on start is probably the result on an excessively rich mixture. Putting your foot on the floor puts the PCM in "clear flood" mode, where it backs off on the fuel it supplies, on the assumption the engine it flooded.

You need to fix the ECT sensor (or wiring, whichever is faulty). If its running rich enough, you're going to foul the plugs, the excess fuel is going to wash the lubrication off the cylinder walls, damaging the rings, and diluting the oil to the point where yuo will get premature bearing wear.

 

Fred,

Thanks! That was my guess as to what was happening but wasn't 100% sure. It's good to know - I just picked up a multimeter so I'll be able to test the wiring side as well as the sensor.

Even if ht set a code for "high voltage", its telling the pcm that the engine is cold, vs. hot?

Thanks again!

 

High voltage = high resistance in the sensor = low temperature. The sensor is a thermistor. Resistance varies inversely with the temperature. Here's a table of resistance vs. temperature, use these numbers to check the sensor:

deg C * deg F * OHMS

-40 ** -40 ** 100,700
-20 *** -4 *** 28,680
0 **** 32 *** 9,420
10 *** 50 *** 5,670
20 *** 68 *** 3,520
30 *** 86 *** 2,238
40 ** 104 *** 1,459
50 ** 122 **** 973
60 ** 140 **** 667
70 ** 158 **** 467
80 ** 176 **** 332
90 ** 194 **** 241
100 * 212 **** 177

 

Gotcha! You are a lifesaver, Fred!