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Acceleration and deceleration

Tiny
JGANAWAY
  • MEMBER
  • 2012 NISSAN QUEST
  • V6
  • 2WD
  • AUTOMATIC
  • 130,000 MILES
When this first happened, the van started to accelerate and decelerate on its own, going up a slight incline and the van was on one-fourth of a tank. We were on the interstate going seventy-five MPH with cruise control on. Stopped and put $30.00 of gas in which put the tank on three-fourths and got back up to seventy-five MPH with cruise control. Didn't have any issues until yesterday. This time, the van was a little below half a tank and I had cruise control on going about seventy MPH. I turned off cruise control and kept it at the same speed and the problem continued. Under a load, there is a whining or a whirring noise too.
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Sunday, October 3rd, 2021 AT 5:27 PM

5 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,716 POSTS
Hi,

I'm not sure I understand. Is the vehicle accelerating and decelerating on its own? Does this happen with the cruise control on or off?

As far as the fuel level, I don't think that has anything to do with it.

Let me know as much as you can.

Take care.

Joe
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Sunday, October 3rd, 2021 AT 6:10 PM
Tiny
JGANAWAY
  • MEMBER
  • 42 POSTS
Yes, it happens with cruise on and off. The cruise will maintain the speed that I set it to until this happens when this problem occurs, the more I press the gas pedal the more it speeds up and slows down, without me letting up on the gas pedal. When this happens, if I let off the gas pedal and give it enough gas to maintain my speed, it doesn't do it as much. Also, the tachometer fluctuates while this is happening.
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Sunday, October 3rd, 2021 AT 7:40 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,716 POSTS
Hi,

When you say the tachometer fluctuates, is it simply going up and down smoothly or does it become erratic?

I'm not sure yet, but I have a feeling this has to do with fuel pressure. It could be an indication that the pump is getting weak. Take a look through this link and let me know if it is something you feel comfortable doing.

You will need a fuel pressure gauge, but most parts stores will lend one to you.

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

Let me know. I feel this is where we need to start unless you notice the tachometer to act in an erratic manner. That would likely be related to an electrical ignition component.

Take care and I'll watch for your reply.

Joe
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Monday, October 4th, 2021 AT 6:30 PM
Tiny
JGANAWAY
  • MEMBER
  • 42 POSTS
Yes, the tachometer moves up and down, smoothly when this problem is occurring.
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Monday, October 4th, 2021 AT 8:09 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,716 POSTS
Hi,

Okay, then it is the engine slowing and speeding up. Although it could be electrical, I would start by testing the fuel pressure. I have a feeling it will be low.

Let me know. One other thought. Let me know if you notice any odd sounds from the exhaust or strange odors.

Take care,

Joe
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Monday, October 4th, 2021 AT 8:14 PM

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