Mechanics

RPMS JUMP WHEN DRIVING DOWN THE ROAD

2001 Dodge Dakota

Transmission problem
2001 Dodge Dakota V8 Four Wheel Drive Automatic 102000 miles

I have had 2 different dakotas and they both have had this problem. When cruising down the road whether it is in cruise control or not the RPM's jump about 2-300 RPM as if it was going to shift. It doesn't shift and then returns back to normal cruising RPM's and then will repeatedly jump like this. Is there a problem with a sensor in my transmission or what do you think it is? Thanks
Avatar
Tribble
September 24, 2008.



Hi: This is an interesting problem. You mentioned that you have two of the same trucks, and they both have the same problem. By any chance, is there a check engine light or maintenance light on? When you say the RPM go up 2-300RPMs, does the engine speed up or is it the transmission which seems to cause it?

My first thought is a MAP sensor, but I need more info. If there is an Auto Zone near you, have them scan the computer and tell you if there are any codes. Here, in Pennsylvania, that is a free service offered by the company.

I do not live close to an Auto Zone to have them do a scan. My computer has not thrown any codes in either vehicle. You did want me to specify whether I thought it was being caused by the transmission or the engine. I would have to say that it is the engine that would be causing the jump of 2-300RPM's. It is almost as if the motor thinks it needs to work harder to keep at that speed but then it backs off like it changes its mind. It repeatedly does this jumping numerous times and then it will not happen for a while. It happens in both cruise control and regular driving using the pedal. It is most noticable when cruising down the highway when the vehicle starts to climb a small incline, or there is a head wind. I recently did a tranny flush with a new filter and gasket kit with ATF +4 fluid and that didn't solve the problem.

Tiny
Tribble
Oct 1, 2008.
Hi: First, I question if there has been a recall on the vehicle dealing with the cruse control. It almost sounds like it kicks on and off. But the fact that you said it does it both with the cruse on and off makes me question that. On the other hand, a ck eng light doesn't have to come on for there to be codes in the computer. The computer will store some malfunctions without you knowing. I almost want to suggest to you to have it scanned regardless. What do you think?

Joe

I could have it scanned by my local mechanic and see if there are any codes that come up. When I find out I will send a reply back to you and let you know. When you mentioned the MAP sensor before, what made you think of that right away? If that was having problems what are the symptoms?

Tiny
Tribble
Oct 1, 2008.
Hi Again: A MAP sensor is an manifold absolute pressure sensor that can cause a change in the vehicles performance. It can do anything from cause poor performance, shut the engine off to exactly what you described. Its purpose is to provide the right amount of fuel and adjust the ignition timing based on intake vacuum. If it advances the ignition timing a slight amount at the wrong time, the engine RPM could change.

Please keep in mind, I'm not there with you, so I'm doing the best I can. If your local mechanic feels differently, let me know what he says and I'll try to guide you from there.

I hope I helped, and look forward to hearing from you in the future.
Joe

I talked with my mechanic last night. He seemed to think that this was normal. He tried to explain that the transfer case is shifting and locking into place and then shifting back. I don't think this is something that is normal. I can see what you are saying about the MAP sensor. It could be adjusting the timing at the wrong time and causing this problem. If it was something that happened once in a while I wouldn't be concerned with it, but like I said it happens repeatedly over and over during travel. Would you recommend I have my mechanic check the MAP sensor system out and possibly see if there are any leaks in the vacuum?

Let me know what you recommend.

Thanks,

Dave

Tiny
Tribble
Oct 2, 2008.
Hi Dave: I'm not sure what the mechanic is talking about because the transfer case doesn't shift gears. Regardless, I think you should have it scanned to see if there are any codes stored in the computer. I hate to make such recommendations because I don't really want you to spend any money on the scan, but what you have described to me doesn't sound normal. It could be a sensor, vacuum leak.

If you decide to scan it, let me know the outcome.

Good Luck,

Joe

I have an 01 Dak with the 4.7. After the Chrysler dealer installed the co-pilot, we finally found the problem. Voltage/resistance fluctuation on the TPS. From what I've read, the TPS is suspect on Dakotas, well this one didn't set a code as the fluctuation was within tolerance, but was evidently affecting the lockup on the torque converter.

Tiny
74b5roadrunner
Oct 23, 2008.
Hi Dave: I'm glad you got the proble taken care of. I had a feeling it was a sensor, but wasn't sure. It's sometimes hard to identify exact problems over the net. Regardless, I'm glad it's fixed and good luck.

Joe
PS: If you have any other problems, let me know and we'll start over again.