2000 #4 Misfire P0304

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06-17-2022 | 06:27 PM

408Revo

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Model: Cherokee (XJ)

2000 #4 Misfire P0304

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?

Any help is greatly appreciated. thanks

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