Yet another problem with my 1993 B150 3.9L. When it's damp the engine is almost impossible to start. Rotor and cap are new. Fuel delivery system is working perfectly. To my knowledge the SMEC is working just fine.

Today it was cold & wet outside and I had trouble starting the engine. In desperation I fired up my Mr. Heater forced-fan propane unit and directed it under the engine to warm & dry things for about 5 minutes. Engine started and ran fine.

Is there a sensor (or something else) on the engine that is so sensitive to wet weather as to stop the engine from starting?

 

Having A new cap and rotor is great, but Old spark plug wires when damp (or not) will cause all sorts of strange issues.

Many years ago, I had a 14 month old set that looked as good as new and was having hesitation issues.

Exasperated, I went to a good diagnostic guy who ran the gauntlet of tests and found everything normal. He sprayed the wires with h20 and the oscilliscope started going haywire.
A new set of spark plug wire leads made a huge difference in driveability and eliminated the hesitation.

The connections at the distributor/ coil and plugs looked fine. So did the insulation on the wires, but they were not.

Try and make sure none of the your new wires are touching each other or anything grounded.

You could try removing one wire at a time and cleaning it with wd-40 and checking the contacts for green corrosion, but this takes longer than just replacing them thereby eliminating the wires as the damp no start culprit alltogether.

 

The intake air temperature sensor is another possible culprit.

 

Landyacht318 - thanks, I'm going to change the wires to a custom-fit OEM set from Bosch. Alloro, where is the intake air temp sensor located?

 

If I may, the "charge air temp sensor"(as chrysler calls it) on our trucks is on the right side of the intake manifold near the front. It has a two wire connector with one wire being black/light blue and the other being black/red. With the engine warm the resistance should be less than 1340 ohms.

 

Is it?

 

Thanks - since I'm having an engine starting problem can someone tell me also what the resistance should be when the engine is cold?

 

I has similar problems, no start on damp or wet days.. cleaned and checked, and replaced old corroded ground cables, and problems resolved, and a cheap fix to try early!

 

OK, I would like to check this also. Where are the ground cables you speak of located?

 

The Main grounds are the one from the battery negative to the engine. The engine to the chassis frame or firewall. Usually a redundant one from the battery directly to the chassis as well. The idea is to have all structural metal connected to the battery negative. Any single wire which is attached to frame/ firewall/ or engine is a grounded wire.
Make sure all are clean and tight There are many grounded wire locations inside and outside the firewall( on my '89 anyway), and the thick wire from the battery itself can appear okay but have high resistance and cause all sorts of problems.

I've also seen clean looking battery terminals intermittently not pass any current to the wires.