I got a 2000 xj, probably 2 months ago. Previous owner swore that it never had any engine issues (ya right) so don't really know the history on it. About a week ago I was on a 30 min drive on a highway and rev'd up the engine to about 3500 rpm and the car instantly became nonresponsive. Felt like the engine turned off. The check engine started blinking. As I released the gas I was able to keep driving with check engine blinking. Hooked up the scanner and I saw "confirmed" code P0304, cylinder #4 misfire. I changed the coil pack and plugs and cleared the code. Took it for a test drive and it did the same thing. This time as saw codes P0303 and P0300 as "pending". I checked the fuel pressure with the car on idle and read 59psi. As soon as I turned off the engine, pressure almost dropped instantly to about 49psi and then to about 30 psi at a much slower rate where it stayed.

Engine compression: #1 -150psi, #2 - 160psi, #3 -160psi, # 160psi, #4 - 160psi, #5 -150psi, and #6 - 150psi. Checked compression after engine had warmed up.
Plugs have a light white coating on almost all of them.

Last thing I did was swapped the fuel injector from one cylinder to another. At first I thought the issue had gone away. I was driving it in town for about 30 mins and rev'd up the engine in the 4000s and no issues. Later on took a 30 min trip on highway and it did it again. Confirmed P0304 and Pending P0300/P0303.

Question, is it normal for the fuel pressure to drop so fast and could this be the issue why I'm getting misfire on #4? The only thing that throws me off is if it was the fuel pressure, wouldn't I be getting confirmed codes on all cylinders?
Could a bad fuel filter cause fuel pressure problems?

Any help is greatly appreciated. thanks

 

If your fuel pressure sucked it would affect the entire rail...not just cyl 4...what are the pending codes 300 and 303

 

Correct. Pending codes are 300 & 303. The only confirmed code is 304.

 

Thing that is bugging me is the fuel pressure.
Not that fact that it is dropping but that you got a reading of 59 psi at an idle.
Almost positive it should be 49 +/- 5 in an '00 at an idle.

 

Is that the original (0331) cylinder head?

Problems with cylinders 3 and 4 on an 0331 is always a high-anxiety issue.

What do the plugs look like?

Check for actual spark while it has the issue. Could be a coil driver (although they tend to either work or not).

 

What brand of fuel pressure tester are you using?

 

Ralph77, thanks for catching that, it was a typo on my end. Fuel pressure is 49psi at idle.

 

Dave51, it's not the original head. Discovered when replacing the valve cover gasket. With about 50 miles on the new plugs, they have a light white coating. other than that they look good. Coil pack is new and has spark.

 

I think I might have found the issue. While I was looking inside the engine bay I noticed something wet around the fuel line. Sure enough, there was a good size leak right around where the fuel line bracket/clip attaches to the manifold. I will check back with results once I replace the line.

 

finally got the new fuel line installed and I'm somewhat puzzled. I was about 20 mins into my drive when I saw the check engine light flash for about a second and then it just went away. About 20 mins later I was going about 65 mph and let get of the gas and the check engine light flashed for a second and went away. I then took it for another trip for about 1hr drive and no issues at all with the exception that right before getting home I decided to rev up the engine on first gear and right about 3500rpm the light flashes again for a second and then goes away. I checked the codes and I'm seeing P304 as pending only, nothing confirmed. All three times when the light flashed I did not feel any power loss at all. One thing that I forgot to mention at the beginning of my post is that when I got the first misfire I had just put some gas, about 1/2 tank. Today before taking it on the drive I was about a 1/4 tank and I filled up almost to 3/4.
There has definitely been great improvement from before to now. Before 15 -20 mins into a drive I would start getting misfires, check engine light on, light flashing, and complete power loss. Today. if I wouldn't of seen the light flash for that second I would of thought the issue was completely gone. Any thoughts as to why the problem is basically gone but not all the way? Is it safe to say that there was a fuel issue? Is getting bad gas now a days even a possibility? I remember hearing about bad gas years ago but never experienced it.

 

Update. The problem is gone. Not sure if it was the fuel line leak or potential bad gas. Still wondering why I was only getting a confirmed cylinder #4 misfire. I would think the fuel would affect all cylinders. Thanks everyone for the help.

 

Glad it is fixed.

 

Glad its gone, but I wanted to ask since I didn't see it in the original post... Did you replace or rebuild the injectors? I ask because I had some issues that were somewhat similar with my '00 and I ended up correcting them with new o-rings as mine were starting to dryout.

 

I did replace the injectors when I replaced the leaky fuel line. I honestly don't think the injectors were the issue on my xj. I swapped injectors from one cylinder to another to trouble shoot as a potential issue and was getting the same misfire on the cylinder #4.
What codes were you getting on yours or was it just misfires?