What's wrong with my truck?

October 21, 2009 10:37 AM

I have a 2001 Dodge Ram that I use when I need to haul things. It runs great, except in the morning after it rains. The truck will not want to rev beyond 1800-2000rpm. If I idle it or drive for for about 10 minutes the problems go away. Any ideas?

This has been happening for about a year but I don't use it very often so I sort of ignored it. I've been using it a bit more and I sort of want to get it taken care of if it is causing damage, if it is not I can just ignore it. It is also an automatic so I'll try to explain gear changes as best I can, but I could be wrong. Keep in mind this only happens in the morning after a rainfall. It did occur once without rainfall, but in that instance I parked it in a field that was very dewy; there's definitely a moisture connection. I haven't noticed the problem if I drive it on a dry day and it rains in the afternoon. Here's the best description I can come up with:

It will make the transition from first to second at about 1800rpm so I don't initially notice it. From second to third, on normal conditions, it'll get up to 2400rpm before changing gears. When it is experiencing problems it won't go above 1800rpm or 2000rpm and if I apply more pressure on the accelerator the engine sounds like more power is coming out of it but the tachometer doesn't seem to want to move up. It is as if I hit a ceiling or there's a hole at around 2000rpm. If I accelerate slowly I can get up to the speed I want without any problems. This is really noticeable when getting on the highway and I need a lot of torque to get up to speed. If I push it when I hit this "wall" , and I only did this once, it gives up and drops down to like 1600rpm. I don't know if I would describe it as a popping sound or just a cessation of power? When I did this (just once!) the engine light came down, when I let off the accelerator the engine light went off. It has yet to come on again.

It is most definitely every single morning it rains the night before, I've been driving it everyday this last month to isolate the problem and to make sure the rain thing wasn't a red herring. I'm really confounded as to what it could be.

posted by geoff. to travel & transportation (9 comments total)

Is this a gas or diesel truck? If gas, I'd suspect the distributor is getting water in it (and the engine heat eventually dries it out, making the problem go away). Also maybe a plug wire problem.

Try taking a spray bottle of water (not a hose) to the distributor and plug wires and see if that recreates the problem.
posted by zippy at 10:48 AM on October 21

Check your plug wires. Spark energy above that RPM level may be enough to jump out of nicked wires.
posted by notsnot at 10:57 AM on October 21

belts slipping under moisture?
posted by artdrectr at 11:01 AM on October 21

Even though your check engine light is off now, the trouble code is probably still stored in the memory. If it flashed when it came on, you're having a misfire or multiple misfires. .
I'm going with zippy on this one. Moisture related misfire. Sounds like what's happening is that the spark that should be going through your coil(s) and wires is finding another path to ground via the excess moisture in the air and in the engine bay.
If you wait until evening to do the spray bottle test, it should be dark enough that you can see the sparks fly.

As far as your transmission shifting goes, it sounds like it's working fine. The transmission shifts based on speed, RPM, and load. What's happening is that when your speed and RPM are constant and the load is increasing, it doesn't shift up. It's staying in gear to keep the engine in its power-band. Totally normal.
posted by Jon-o at 11:03 AM on October 21

moisture in the distributor or wires. change them both.
posted by Gungho at 11:04 AM on October 21 [1 favorite]

If it is a Hemi, it has a long boot on the end of the sparkplugs that could be allowing moisture in. Try spraying is some WD 40 around the end of the sparkplug wires next time it does it. Despite most people using it for a lubricant, WD 40 was created to do water displacement. If it helps, get new plug wires. if not, then I'd change the distributor cap.

If you have a diesel, I'd take a look at the fuel filter and run some water remover in the next tank.
posted by midwestguy at 11:16 AM on October 21

You guys are great! Changing the distributor and wires should be easy enough, I'll try to get to it tonight and let you know how it goes.
posted by geoff. at 2:34 PM on October 21

If you've never done this before, don't take all the wires off at once! Move them onto the new distributer cap one at a time. It's easy to get flummoxed with everything disconnected.
Good luck!
posted by Jon-o at 3:07 PM on October 21

I had this exact problem (moisture related starting/warm up issues) on my 1997 Chevy Silverado. I changed the cap and rotor and that was all it took to eliminate rough running in the rain, no start after rain, long warm up times, and misfires at constant highway speeds.

Good luck. I know how frustrating this problem can be to track down.
posted by bugsoup at 4:21 PM on October 21