Chevrolet Repair: Hard starting 1989 GMC 4.3L V6, coolant temp, temperature gauge

Question
I experienced some rough idle in my 1989 GMC C1500 automatic (4.3L V6, 140,000 miles) and the 'check engine light' came on indicating code 15 (cooling sensor open circuit). The dash temperature gauge is working fine and the engine temperature is within normal range. The problem is that when the engine is hot and I disconnect the battery to clear the code, the engine will crank but not start - left overnight it will start but run rough for 15 to 30 seconds - code 15 shows. I can hear the fuel pump working and I have spark but it may be weak. I changed the ignition coil and this has improved the overall performance. New head and valve cover gaskets, fuel filter, distributor cap, rotor, plug wires and plugs (Champion) about 7000 miles ago (14 months ago). Yesterday after changing the coil, engine started and after 15 seconds of rough idle (code 15 again), ran extremely well for over 1 hour. Engine was then shut off and restarted twice, no problem, however once the battery was disconnected, it cranks but will not start. Battery was fully charged and load tested - o.k.

Your thoughts would be appreciated.  

Answer
Hi Walley, You need to replace the coolant temp sensor and or the harness thats plugs into it. This sensor is located next to the thermostat and has 2 wires. Be surethat it is plugged in, check to make sure the wires are not broken or coroded. If this all looks good replace the sensor. This sensor tells the computer how warm the engine is and if open it sends a temp reading of -34 degrees (now thats cold). This will make the engine run very rich!!

Have a Great Day


Mark