# Sentra 98 started bucking, need help.



## antimoine (Apr 27, 2008)

Hi, I just started to have this veeeery annoying issue with my sentra, it goes on fine for a while and then starts bucking at different revs and at different speeds. It's not constant at all, it starts at lower speeds, then I go on the highway for a while, goes ok at 80-90 km/h starts bucking at 100, does it every few seconds afterwards. The thing is when I use lower speeds after that, it goes fine for a while again (few minutes). Now, the distributor cap, spark plugs, cables, air filter and air tubing were changed. I have to fix this fast, I did search the forums but there was nobody with the same issue.

Oh and it started happening after I filled the tank when it was very close to be empty.

And btw I am a :newbie: if you can please tell me what the acronyms mean when you use them that would be awesome.

Thanks in advance


John


----------



## antimoine (Apr 27, 2008)

Ooooh, I must say that I did not read carefully all the pinned topics, I did the ecu code thingy and it got me 34. I am currently searching this as we speak, if anybody can help me and maybe describe the next possible course of action that would be very aprrecianted.

Thanks again.


----------



## IanH (Feb 11, 2003)

so 34 is 0304, and the table says Knock sensor.
Download the FSM and phatg20.net for you car and go from there.
You can also get the code read for you at the Auto parts stores like Autozone.


----------



## antimoine (Apr 27, 2008)

weeeell, I did reset the ecu and now I gives me code 55 (all is good). It did it again a few times this morning and still code 55. I have to say that it did take quite a while before it started doing it again.

It is raining today, the engine was hot, had been running for a few minutes, and I went for a ride with no trouble whatsoever, the trip back was less pleasant unfortunately but still, no difference in engine temp or error code, only running time.

Heeeeeeelp


----------



## IanH (Feb 11, 2003)

Well if there is no code there is not much to go on.
Try re-cleaning the MAF connector
Check all the connectors and HT wire connections.
also change Fuel filter and maybe add a Fuel additive to the tank.
Good Luck....


----------



## antimoine (Apr 27, 2008)

MAF is mass air flow right? I'm reading the service manual and want to make sure.

So it could only be something dirty or clogged giving no error code, or a defective sensor, that's gonna take a while......

I'll post if I find something new. thanks for the replies


----------



## IanH (Feb 11, 2003)

YES the MAF is the mass air flow sensor. 
Most common problem with dirty control valves is the IACV, search and you will find info.
normally this gives problems just at idle or just off idle.
Also try the injector connectors.
check the little rubber hose at the bottom of the EGR valve/actuator, they rot out, although when mine went it threw a code and didn't buck...


----------



## bgsentra (Jun 23, 2006)

have you checked your timing recently? That could be causing the knock sensor code.


----------



## antimoine (Apr 27, 2008)

I must say I did not. I don't know how to either(yet). I'll start searching for that too.

I did clean every hose and pipe I could see, but i'll test it tommorow only on a long ride.
so far so good


----------



## bgsentra (Jun 23, 2006)

Heres a great write up on how to check your timing. You will need a timing light which should be around 30 bucks. http://www.nissanforums.com/ga16de-1-6l-engine/118530-definitive-guide-how-adjust-timing.html


----------



## antimoine (Apr 27, 2008)

It did it again this morning (aargh). I'll check the timing, it does make sense though cause the knock sensor code is just a symptom of what is really happening. I mean something not giving me a code is making the engine jerk/misfire/buck and in turn trips the knock sensor. sounds right ?

It started really weakly, I first thought it was the bumps on the road but soon enough it became rather evident.

The feeling is quite the same as if you release the clutch on first speed without giving gas, you know, like a small forwards-backwards motion, not a rough one but enough to feel it. 

I did find the info on how to test the o2 sensor as well in the manual, with the ecu and the engine on, I'll try that too just to see

Edit: there is a rattle sound coming from the engine, could it be timing again ? would it give me a code or something? I'll try to find from where the rattle comes from.


----------

