My 95 GMC 6.5 TD had a toggle switch under the dash for cold start. The previous owner told me to flip it when it was cold and truck would start better. Idle was increased about 150-200 rpm It worked very well.


I was getting a code 15, 33, 34 and replaced the engine coolant temp sensor in the crossover pipe. When I unplugged the connector from the sensor I saw some soldered wires that I traced back to the switch under the dash. Basically the yellow wire to the sensor was cut and wired through the dash toggle switch. Switch on, opened the yellow wire circuit. It has been about 36-40 degrees every morning up here and truck started much better with the switch then without. (Truck was not plugged in). QM had posted that the yellow wire is 5V to the sensor and sensor resistance on black wire tells temp to ecm. What effect does breaking the yellow wire have when starting? More fuel?

Advance goes to 14 deg. and fuel is increased. My big concern was that the truck should be able to start without the switch if the glowplugs and the battery connections were good and steelydan said h had to start it three times before it stayed on.

Is that what makes the ECM "think' it's -40°?

Yes.

I put a time delay relay instead of a switch in my 95. About 5 seconds after it starts, the relay turns on and closes a contact, restoring normal temp reading to the PCM.


My truck starts much better with the extended glow time and 60G glow plugs when cold.

ToddMeister - Can you give us specifics on the relay? Part #, where to get? maybe come over and install it? http://www.dieselplace.com/forum/smileys/smiley17.gif

I used an Amperite relay 12DSPDT.1-60C, available from Newark Electronics or Allied Electronics, 20 or 30 bucks IIRC.


Newark Electronics: www.newarkinone.com (http://www.newarkinone.com/) Phone 800-463-9275


Allied Electronics: www.alliedelec.com (http://www.alliedelec.com/) Phone 800-433-5700


It's kind of a long drive to install it - sorry.

I wonder if the increased fuel and timing advance screws up anything if used all the time? I only use mine when it is cold, any other time it starts fine. Can someone more experienced comment?


Dan

Dan, if used all the time the truck will idle fast, because PCM thinks engine is cold. Advanced timing may be hard on the glow plugs and head gaskets, too.


I've been using the relay setup for over a year now, works great.