Car bucks when hitting 6,000rpm

G

Ge0rge

Member
Location
PA
Car
2008 FX35 AWD
When I got on the gas pedal this morning I noticed the car was 'bucking' once I hit 6k on the tach. It was like I was off/on/off/on the throttle really fast, as if it didn't want to shift. It would then shift but not without such an incident. Otherwise the vehicle seems to run great. Any thoughts?

2008 FX35 w/Sport and Navigation Pacakges
 
Ge0rge said:
When I got on the gas pedal this morning I noticed the car was 'bucking' once I hit 6k on the tach. It was like I was off/on/off/on the throttle really fast, as if it didn't want to shift. It would then shift but not without such an incident. Otherwise the vehicle seems to run great. Any thoughts?

2008 FX35 w/Sport and Navigation Pacakges
Click to expand...

in 1st or 2nd gear?
 
Thanks for replying. I tried it once going 45mph. I would mash the throttle, it would take off, and then get to 6k and act up, sometimes quite bad. It was literally like I was pedaling the throttle real quick, almost like it was missing a bit.
 
Tach tends to jump back and forth between 6k and 6.5k. The engine sounds like it is missing.

---------- Post added at 10:27 AM ---------- Previous post was at 10:26 AM ----------

I am wondering what it would do if I was in auto-stick mode. When I leave today in a few short hours I will take it out onto the highway for a test run.
 
I have a couple of ideas.

First, I would check your coils and spark plugs. Is the car throwing any codes? You might need to go to an auto store to get codes read. I'm hoping one of those things is your problem. If not...

I had something similar that ended up being my ECU. In the battery compartment there is a rubber boot that waterproofs the firewall where wiring enters the cabin. Have you run any new wires through there? Check to see that it is still sealed - if water can penetrate that boot, it will run down the wires inside the cabin and into your ECU under the glove box - causing permanent damage. I had to replace my ECU after it got wet. Took over a year to finally figure it out. The problem never got worse for me - it stayed annoying and I learned how to "drive around it". For a diagnosis, I had a shop hook up another ECU (from a G35) and we could not reproduce the problem. After replacing the ECU, the car behaves normally again. Hope this is not the problem for you.
 
Is there a way to check for codes without a reader? My old car threw codes on the digital odometer. I will likely take it to the dealer for a diagnosis/repair. I have not done no work to the vehicle as I only got the car 2 weeks ago. I am not upset, its part of the process on used car ownership. It still has warranty and I purchased a bumper-bumper warranty as well.
 
Sounds like you are hitting the rev limiter but that doesn't make sense. If the check engine light isn't on then there isn't a code. It is possible to check in the car using the pedal method though.
 
My old car (Altima SER-VQ35DE) did that when I ingested water into the intake during a storm. No CEL either. I know it's a long shot but have you had anything like that happen?
 
Last edited:
No water that I am aware of. Could it be the gas I am running. I am running a mini-mart gasoline that I had good success with while owning my last car. I used 93 for the 2 tanks I filled so far. This last tank I added 1 bottle of Chevron with Techron fuel system cleaner. It was the smaller size made for 12 gallons of gas.

---------- Post added at 12:20 PM ---------- Previous post was at 12:20 PM ----------
StuLax18 said:
Sounds like you are hitting the rev limiter but that doesn't make sense. If the check engine light isn't on then there isn't a code. It is possible to check in the car using the pedal method though.
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What is the pedal method?
 
Ge0rge said:
No water that I am aware of. Could it be the gas I am running. I am running a mini-mart gasoline that I had good success with while owning my last car. I used 93 for the 2 tanks I filled so far. This last tank I added 1 bottle of Chevron with Techron fuel system cleaner. It was the smaller size made for 12 gallons of gas.

---------- Post added at 12:20 PM ---------- Previous post was at 12:20 PM ----------



What is the pedal method?
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The quality of the fuel could be part of the problem. Not really sure that it would only affect the upper RPMs though.
 
Thanks, I will try it out.

---------- Post added at 06:44 PM ---------- Previous post was at 01:06 PM ----------

I seem to have gotten codes # 7 (could be eight, this being the last quick blink)

#39
#1102.

Is there a list on the forum telling what each one is? I was unable to find it using search. Thanks.

I noticed the tach tonight really jumped around when this happened. It did it tonight at 5k on the tach starting once I floored it at 40mph. From a dead stop this does not appear to happen.
 
The MAF sensor is plugged in. The car did this today around 5k. I pulled out hard, got to around 50 and the car went WAH-WAH-WAH-WAH-WAH real fast. Then it shifted and went back to normal. I am able to make it do this if I am doing 50mph and tromp on it. It will usually act up between 5-6k. If I drive normal, without a heavy foot, I don't get the problem. Could it be a tranny issue?
 
GeOrge - this sounds EXACTLY like my ECU problem. Your, WAH, WAH, WAH was how I described it myself. It happened exactly in certain rpm ranges and no other time. Doesn't matter what gear, does it?

I think you have some ECU damage. Maybe from water, maybe from an electrical problem. It won't get worse in my experience but it can't be good for the motor. Unfortunately the only solution is replacing it and having the dealership reprogram your keys. It's a $1000 part so the warranty people might fight it for a while. I really think this is what you have and you should seriously consider yourself lucky somebody else had the same issue. I was in the dark for more than a year.

Absolutely follow other's advice if you wish - just keep this diagnosis in your back pocket for when all else has seemed to fail.
 
I will call the dealer on Monday. Hopefully I don't have to fight the battle of my life just to get this fixed. Thanks for your help.
 
jumbosrule said:
Absolutely follow other's advice if you wish - just keep this diagnosis in your back pocket for when all else has seemed to fail.
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I called the dealer which is 50 miles away. They set me up to come down first thing and take it for a test run to cause the problem. I will have to push it back until at least next Monday. I told him the same thing I posted here as well as what was the cause of your issue. He was interested in hearing anything I could give him. I will let you know the outcome. I wonder what the loaner will be, my luck it will be a cobalt.
 
We took the car for a test ride, I got it to act up luckily, and back to the garage we went. He hooked up the computer, it read upwards of 115%, meaning it was running rich while at idle. He connected a test MAF sensor and it dropped to the level it should be of 103% give or take 1 or 2 %. They had to order one, I go back Friday for the install. He said the big thing they see lately is with the new G models which have 2 air intakes, with 2 MAF sensors and then the owner installs K&N type filters, over oil them, and it damages the MAF sensors. He said it really is not worth the tiny bit of hp you may get.
 
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