Hi,
I have 2003 Touring model with 26k miles, I bought it used and at the time of the purchase it seemed flawless. After few weeks of driving it started having problems, engine thumping is relay hard(it shakes the whole car) and car does not accelerate as it should. When I took it to mechanic they told me that it had code P0300 (random cylinder misfire). Now the weird thing about it is that it goes away at random and then comes back, when it goes away car operates as it should smooth engine thumping and it accelerates as it should. After allot of time in shops they told me that it was bad coil which we replaced and it seemed to fix the problem for short while. After month later same problem started again and when taken back to shop I was told that it is happening but it goes away too fast for them to nail down the problem.
I also found out that car had some kind of after market alarm system that taped in to coil wires to prevent it from starting(maybe those 2 way pager alarms) and it was take out by previous owner, but there is still some wiring left and sensors on back bumper. My quest is that incompetent shop installed system and when it was removed left over wiring shorting something out (since it work fine at times).
Am not really sure how to proceed with this issue and any advice or suggestion is greatly appreciated. Or maybe there is some good shops who know Z's around Irvine area... Thanks for your help.

 

What do you mean by engine thumping? You need to try to paint a better picture for us on what is exactly happening so we can try to help you out.

.

 

Basically the way engine is spinning. When it work fine it's smooth and quiet with little vibration, when that issues comes back it's start shaking like its about to stall(and it doen't) but it's consistent through out rpm range, noise becomes a little deeper(more like v8) and longer duration between cycles, sounds almost like popping at higher speed. Then faster u go then more and faster it shakes. Feels like one(or more) cylinder is constantly misfiring creating vibration and loss in power. Sorry I am not sure how else to describe it, english is my second language. help

 

You said that you took it to a mechanic? Was this the Nissan Dealership or a general repairs type mechanic?

 

At first it was taken to nissan, after 2 days(and 200) I was told that it might be electrical and they need more time and about 400 more estimate to nail it down.
Car is 03 and out of basic warranty so I was not prepared to pay 600 for diagnostic and god knows how much more to fix it, so I took it to my mechanic (i trust them with my cars, they worked on my 230 fwhp NA ford focus and my other moded cars). They switched coils to different cylinders and as they say problem followed the coil, so we replaced them.

 

shameless bump pls help >_<

 

After doing some more research I came up with that most of the time it's bad wires, coils, spark plugs or fuel injectors. Seeing that problem is not persistent I am pretty sure that it is "left over alarm wiring" that causes this since it had remote engine start, back up sensors and lots of wiring left over. Will be taking it to alarm shop tomorrow to take all wires out, hopefully that will take care of it.

 

Funny thing is my car sorta does the same thing. I have ordered a Crank Angle Sensor located on the bellhousing/engine since they have been know to go out alot. Now I'm not saying that will fix my problem but at this point it is a process of elimination for trouble shooting my car wanted to die when coming to a stop...
brooke