Probable cause for 5.4 misfire?
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Junior Member
Joined: May 2007
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Probable cause for 5.4 misfire?
First of all, thanks in advance for your help. This forum and its collective knowledge are priceless.
I’ve done searches on this but I never quite found the same problem/solution.
My 98 Navigator (5.4, 100k miles) gave me a P0304 error the other day. I’ve had some trouble getting to the root cause of the misfire because of the poor access to the #4 cylinder. Normally I’d check the spark and/or compression but as you all know it’s kind of hard to do once you’ve torn it down enough to get at the COP and plugs.
So far I’ve done the following:
Cylinder leak-down (OK)
Primary and secondary coil resistance (OK)
Observations:
Plugs indicate cylinder #4 is running lean; gap had opened up to .065”
Top of COP is coated with “muck”(oil or coolant mixed with dirt?)
Heater hose over #4 has screw-type clamp (originally a spring clamp?).
Coincidently (or not) about 6 months ago I replaced the PCV vacuum line that runs right over cylinder #4 because of the well-known elbow problem.
Seeing as the truck has 100k on it it’s due for some replacement parts but I want to make sure I have the problem solved before buttoning this thing back up. Also these engines with MPFI and COP’s are new to me from a service/repair standpoint.
Based on your collective wisdom what should be my next steps and what parts should I plan on ordering?
I’ve done searches on this but I never quite found the same problem/solution.
My 98 Navigator (5.4, 100k miles) gave me a P0304 error the other day. I’ve had some trouble getting to the root cause of the misfire because of the poor access to the #4 cylinder. Normally I’d check the spark and/or compression but as you all know it’s kind of hard to do once you’ve torn it down enough to get at the COP and plugs.
So far I’ve done the following:
Cylinder leak-down (OK)
Primary and secondary coil resistance (OK)
Observations:
Plugs indicate cylinder #4 is running lean; gap had opened up to .065”
Top of COP is coated with “muck”(oil or coolant mixed with dirt?)
Heater hose over #4 has screw-type clamp (originally a spring clamp?).
Coincidently (or not) about 6 months ago I replaced the PCV vacuum line that runs right over cylinder #4 because of the well-known elbow problem.
Seeing as the truck has 100k on it it’s due for some replacement parts but I want to make sure I have the problem solved before buttoning this thing back up. Also these engines with MPFI and COP’s are new to me from a service/repair standpoint.
Based on your collective wisdom what should be my next steps and what parts should I plan on ordering?
Registered User
Joined: Jun 2006
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they are known for a heater hose leak and drip onto the #4 coil shorting it out. check that first. if it were me and i had no diag equipment id swap that coil with say #3 and see if 3 starts to missfire then you know its the coil.
Last edited by Adam06FX4; May 29, 2007 at 10:46 PM.
Thread Starter
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Junior Member
Joined: May 2007
Posts: 3
Likes: 0
I've been reading about the heater hose leak but it looks like someone took care of this already (screw-type clamp). Also would this cause it to run lean?
I've been dragging my feet with swapping coils because it seems like a real pain to swap back and forth and then maybe replace. Is there an "easy/quick" way to get to the coils?
Thanks.
I've been dragging my feet with swapping coils because it seems like a real pain to swap back and forth and then maybe replace. Is there an "easy/quick" way to get to the coils?
Thanks.
Registered User
Joined: Jun 2006
Posts: 746
Likes: 0
well you could just go out and buy a new coil which is 99% of the time the problem. as for your lean condition if its not throwing a code dont worry. almost all the plugs i pull out of those engines are pretty white.