4.7l p0300/p0304 - JeepForum.com
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post #1 of 4 Old 09-26-2017, 04:21 AM Thread Starter
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2001 WJ 
Join Date: Sep 2017
Location: Washington D.C. area (MoCo)
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Question 4.7l p0300/p0304

I'm having this issue with my WJ 4.7L Limited 4wd. I'm turning to the forums to seek help on resolving this issue. The motor will fired up after some long cranks. It will bog down under-load (feel like fuel pressure starving). The CEL light came on and I pulled the code it throwing a P0300 (Multiple Misfire-Detected) and P0304 (Cylinder 4 Misfire Detected). I even check the fuel pressure at the schrader valve on the fuel rail and it's loosing pressure. I'm starting to loose my patient on this WJ.

Here is what I have done
Fuel pump assembly with a Delphi last week before that fuel pump was replace 2-3 years ago with an Airtex.
Fuel Filter was replace 6 month ago (can't remember the brand).
All Spark plugs was replace about a month ago along with 2 or 3 coil packs

After I replace the fuel pump it does not loose fuel pressure anymore while it's under-load. It still loose pressure while the motor is off or sitting at a stop light for awhile the car tend to misfire.

I order (1) OEM fuel injector thinking it could be a leaky injector on Cylinder 4 that leaking inside the Intake Manifold. When I change out the Injector should I put motor oil on the O-ring or silicone?

Is there anything else I should look into?
I appreciate if I can get some insight and some type of direction on resolving this issue.

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post #2 of 4 Old 09-26-2017, 10:33 AM
Double E
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2004 WJ 
Join Date: Oct 2003
Location: Raleigh, NC
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Yes on the motor oil to ease installation. Silicone will not hurt either. I do not think the WJ is picky on that but I've not done it before either.
The pressure drop when stopped (engine running) is strange. It does point to a leaking injector among other possibilities.

If that injector does not resolve the issue though, you're going to need to approach the issue with a wider scope of possible issues and verify you have good compression.
With good compression, you know you have the fundamental part of combustion taken care of and can chase the issue via Cam Sensor or some electrical issue such as PCM.

'04 Freedom Edition HO & '04 Overland HO (previous '00 Laredo 4.7)
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post #3 of 4 Old 09-27-2017, 07:06 AM Thread Starter
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Thanks for the advice. I will post my result once I get the Injector replace (Injector still in transit).
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post #4 of 4 Old 10-02-2017, 05:03 PM Thread Starter
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2001 WJ 
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I put the new injector in. Let it ran for about 5 minutes the motor got allot better once the motor started to warm up. Then I shut the motor down because found Injector on cylinder 2 is leaking from the top. I work on it this weekend I think I may have rip the top o-ring .

I also lost (1) fuel rail bolt for the right bank front. I have no dam clue where that bolt went. I did not remove the coil pack or fuel rail. I know for a fact it did not fall in those holes.
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