P0301 troubleshooting - 2004 TJR

[AdventurePig]

2004 TJR, 70k miles. Auto, 4.0l, good shape overall.

2yrs of solid running with no check engine light and About a month ago P0301 code illuminated the engine light, though, it’s my understanding that multiple single cylinder misfires were detected that didn’t show up on the dash display(Going to put a scanner on it tomorrow and see if those are still there)

So far:
1.New ECHLIN coil rail
2. Injectors cleaned and tested
3. Air cleaner (K&N FIPK) cleaned/oiled
4. Fresh BOSCH OE double fine wire Iridium plugs
5. Head: Checked for cracks, surfaced and valve job with new seals
6. New head gasket, intake/exhaust gasket. (Signs of coolant in several cylinders)
7. All cylinders compression tested around 155-160 psi

After all those repairs, Runs well, but still tiny bit of a rough start-up that never happens at idle or while running.

Annnd, popped a P0301 code again this morning on my PM commute.

Thoughts?

Hope to gather some live data with my new tool in the next few day

 

[ItchyDong]

- Get rid of the K&N
- Pretty sure those plugs are no good
- You “tested” fuel injectors how? Did you verify injector pulse with a noid light?
- Stock injectors?
- Check the wiring that runs behind the valve cover. Being an 04, I think you have the plastic conduit that protects it, but still worth a look. The noid light will show any discrepancies here. Wiggle the wiring while testing.
- Injector balance test may be in order. (Or just swap #1 injector with another cylinder and see if your code moves.)

 

[macleanflood]

Could be as simple as needing new o-ring injectors or time for a new crank position sensor.

What's your fuel pressure at?

-Mac

 

[ItchyDong]

Could be as simple as needing new o-ring injectors or time for a new crank position sensor.

What's your fuel pressure at?

-Mac

Yeah it could be. But being that it’s a (I’m assuming) consistent 301 code, fuel pressure and crank are probably not it. Those misfire codes are pretty rock solid.

 

[macleanflood]

Yeah it could be. But being that it’s a (I’m assuming) consistent 301 code, fuel pressure and crank are probably not it. Those misfire codes are pretty rock solid.

Yup just like to eliminate variables and a quick fuel pressure test eliminates that as a possibility. Although I have added a gauge to my rail and am considering putting in a remote sensor and gauge inside.

-Mac

 

[AdventurePig]

- Get rid of the K&N
- Pretty sure those plugs are no good
- You “tested” fuel injectors how? Did you verify injector pulse with a noid light?
- Stock injectors?
- Check the wiring that runs behind the valve cover. Being an 04, I think you have the plastic conduit that protects it, but still worth a look. The noid light will show any discrepancies here. Wiggle the wiring while testing.
- Injector balance test may be in order.

All work was done by a shop.

- Injectors were cleaned and serviced and I’m assuming tested, on their equipment. Stock injectors - not sure, they’ve been on the rig since we bought it.

- I’m definitely gonna look at wiring more closely this

 

[AdventurePig]

Could be as simple as needing new o-ring injectors or time for a new crank position sensor.

What's your fuel pressure at?

-Mac

Injector o-rings were supposed to have been replaced.

Good question on fuel pressure, not sure.