why does my jeep run better in the rain?

95 4.0 /ax15 has a bog on take off except when its raining. One of you geniuses tell me why. Ignition components or sensor issue? thanks, Joe

only after driving in the rain, or fresh start in the rain?

May be your MAP sensor.

Well, rain will bring ambient temperature down and reduce density of the air.

I've noticed this as well. It has been my running theory that the moisture turns to steam in the combustion chamber, adding greater pressure and therefore increasing power.

Maybe it washes a ton of mud off. :gee:

Red99XJVT said:

I've noticed this as well. It has been my running theory that the moisture turns to steam in the combustion chamber, adding greater pressure and therefore increasing power.

Click to expand...

Nope, you want cool, dry air to make the most power. There isn't enough moisture in the air to make a measurable difference. We hated making runs at Bonneville in the afternoon when it got humid because we would lose speed. Cool dry air is your best friend for making power.

The difference in performance will be the lower ambient temps - cooler air means air is more dense which leads to more power.

FWIW, there was some technical info on this subject some years ago that claimed the moisture in the air had a beneficial effect on power. Water injection was a common feature on large piston aircraft engines back in the day for this reason. And this is what your are feeling in performance. So it claimed.

Why I paid attention to that was I sensed the same performance increase as well.

Don't know. DieselSJ certainly adds some contrary experience and info.

Maybe we are just deluded. Or really like the rain.