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P304 misfire and loud noise

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  #1 (permalink)  
Old 16 Oct 2007, 10:02 am
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Default P304 misfire and loud noise

I have an 03 GT Turbo. Recently engine light came on and car ran rough at idle only. No other symptoms. Checked computer and code P304 (Misfire on Cyl 4) shows only.

Changed plugs... Still the same but after driving to parts store for plugs there is a loud whining whistle noise coming from the front right top of the engine. I visually checked all available hoses and gasket locations but nothing is obvious. weird thing is, the noise goes away from a loaded acceleration above 2KRPM. If I just gun the accelerator in neutral the noise remains. When I turn it off, the noise stops as soon as the engine stops. Seems like a air leak but I just can't find it. I have since changed the wires as well. (dealer purchased wires and plugs) I thought the noise was a belt but it emanates from the right side and all the belts are on the left. Oh yeah... No other symptoms at all. No overheating, no loss in accel, no nothing but a rough idle below 2KRPM and a very loud whining noise.

Anyone have an answer to this before I shove out the bucks to the dealer? I would love to avoid paying a lot of money for something I might be able to fix myself.

Thanks for your help.
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  #2 (permalink)  
Old 04 Nov 2007, 06:03 pm
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Default Re: P304 misfire and loud noise

Any luck with solving your riddle? Last week we started to have what sounds to be the exact same problem with our '03 GT. You cannot hear the whistle until the engine is up to temp. I read out the same P0304 error code. The best I can narrow down the source is on the right hand side of the engine!
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  #3 (permalink)  
Old 04 Nov 2007, 07:45 pm
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Location: San Antonio, Texas
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Default Re: P304 misfire and loud noise

Several ideas.... One: the gasket where the 2 halves of the intake manifold has a split or small hole. Take some WD40 and spray at the joint where the 2 seal. Spray at the joint on the front and back if you can get too it. Spray close and heavy. If you get the right spot then the noise will change or go away... Two : you may have a vacum leak from a hose in that area. With out hearing the noise that's where I would start.... Let me know if that helps.
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  #4 (permalink)  
Old 09 Nov 2007, 09:24 am
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Default Re: P304 misfire and loud noise

Thanks.. I replaced the top intake gasket and the noise still present after the engine is up to temperature. I can here it over the radiator fan. The level of the sound is loudest around the number four intake runner. Do injectors ever make noise?
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  #5 (permalink)  
Old 09 Nov 2007, 11:00 am
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Join Date: Sep 2001
Posts: 27,757
Default Re: P304 misfire and loud noise

A couple of TSB's (Technical Service Bulletins) were issued for your code.

# TSB #1802802 -- MIL ILLUMINATION - MISFIRE DIAGNOSTIC TROUBLE CODE (DTCS) P0300, P0301, P0302, P0303, P0304. *TT (NHTSA ID #10016602, AUGUST 04 2005)


Some more stuff I found:

My dakota puts up the code p0304. Ive had the injectors cleaned, the plugs and wires replaced and the #4 injector has been checked out and is just fine. What else could cause the misfire? It runs great going down the road but the misfire occurs when it's idleing. Could it be a sensor?

had the same problem blew a can of throttle body cleaner through the throttle body with engine running problem went away hasn't come back that was 4 months ago. I think it was sticky valve tried same things you did as well $5 can fixed problem

More to read:

P0304 Code - Cylinder #4 Misfire
Technical Description

Cylinder #4 Misfire Detected
What does that mean?

A P0304 code means that the the car's computer has detected that one of the engine's cylinders is not firing properly. In this case it's cylinder #4.
Symptoms may include:

* the engine may be harder to start
* the engine may stumble / stumble, and/or hesitate
* other symptoms may also be present


A code P0304 may mean that one or more of the following has happened:

* Faulty spark plug or wire
* Faulty coil (pack)
* Faulty oxygen sensor(s)
* Faulty fuel injector
* Burned exhaust valve
* Faulty catalytic converter(s)
* Running out of fuel
* Poor compression
* Defective computer

Possible Solutions

If there are no symptoms, the simplest thing to do is to reset the code and see if it comes back.

If there are symptoms such as the engine is stumbling or hesitating, check all wiring and connectors that lead to the cylinders (i.e. spark plugs). Depending on how long the ignition components have been in the car, it may be a good idea to replace them as part of your regular maintenance schedule. I would suggest spark plugs, spark plug wires, distributor cap, and rotor (if applicable). Otherwise, check the coils (a.k.a. coil packs). In some cases, the catalytic converter has gone bad. If you smell rotten eggs in the exhaust, your cat converter needs to be replaced. I've also heard in other cases the problems were faulty fuel injectors.
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  #6 (permalink)  
Old 07 Dec 2007, 11:19 pm
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Posts: 9
Default Re: P304 misfire and loud noise

FYI: The source of the noise turned out to be a section of the gasket between the lower intake manifold and the cylinder head was missing. The missing section was next to the number four injector. Easy fix.
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  #7 (permalink)  
Old 28 Jan 2008, 04:43 pm
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Join Date: Sep 2006
Posts: 349
Default Re: P304 misfire and loud noise

Hedgapple, what was the easy fix....what did you end up doing?

Terry in Orlando
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  #8 (permalink)  
Old 29 Jan 2008, 09:39 pm
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Default Re: P304 misfire and loud noise

In this case an "easy fix" equated to about four hours of fun over Thanksgiving weekend replacing the gasket between the lower section of the intake manifold and the cylinder head. Complete with the additional benefit of working in an unheated upper midwest garage. :^)
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  #9 (permalink)  
Old 22 Feb 2008, 04:39 pm
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Posts: 3
Default Re: P304 misfire and loud noise

one question: is there anyway to make sure that this is the gasket between the lower intake manifold and the cylinder head before "diving in" ?

I don't want to start the whole thing if it's not really the problem.

by the way, I have exactly the same prb then the OP: loud whistling noise, P304 code, changed the spark plugs, wire, PCV valve but error code still the same
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  #10 (permalink)  
Old 22 Feb 2008, 09:19 pm
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Default Re: P304 misfire and loud noise

I was able to determine source of the vacuum leak by first isolating it to the general area by using a length of plastic tubing as a stethoscope. This is more difficult than you would think. Then to confirm that it was #4 I dripped a small amount of water on the joint between the head and the lower intake manifold. The water plugged the leak and whistle stopped (for about five minutes). After I pulled the injector rail I could see the "missing" section of gasket.
The most difficult part of this repair is the lower bolt for the intake manifold support. I just loosened it enough so the bracket dropped back far enough to pull out the lower intake manifold. Without pulling the radiator I think it would be impossible to start the bolt while lining up the bracket.

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