Chrysler Repair: 85 2.6L hard starting in cold weather, mikuni carb, coolant temp

Question
Dear Roland, First let me thank you for your time!!!!! I have a 1985 voyager(2.6 mitsubishi motor, mikuni carb) In the warm weather it runs like a bear, in cold weather 30 deg. or less it will crank and crank but not start. I have replaced wires,cap,plugs,rotor, ignition coil, but still wont start. i have discovered a trick, although confusing, if i loosen the distributor hold down nut,move the distributor to advance/retard? the timing it fires right up, but i have to move it back or it wont run right!! Can you please help?      thanx, Al

Answer
Hi Al,
You are welcome!
Your observations are relevant. While the manual is 'thin' on details about the spark control system of this engine, it shows that the timing is affected by temperature sensors of both the engine coolant and the intake air. The former is located on the right front of the engine and the latter on the intake air/filter housing. The wire colors black/red, violet/black for the former and black/red, black/white for the latter. No specs for those sensors are given but based upon other sensors from that time period I would expect the resistance should be in the range of 10,000-14,000 ohm when the temp is around 70F, and then as the engine warms to operating the coolant temp should drop down to around 700-1,000 ohms, and the air sensor probably not so low because the intake air never gets as hot as the water, but it should have a lower resistance than at start up. When the temp is below 70F I would expect the resistance to be somewhat higher than the range listed above. So I would locate those sensors and see if they measure across their terminals in that range of resistance and whether it drops as the temp rises. The wires go to spark control computer with the black/red to pin 2 of the 13-pin plug, and the violet/black to pin 12, and the black/white to pin 4.
I would begin there and hope you find the fault at one of those two sensors. After that, we get into the timing modification circuitry which will be more challenging for lack of details.
Roland
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