Help - no 4 cylinder miss fire Again??

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Dukernc

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Ok so last week the CEL came on and I ended up getting the code P0304 which is engine misfire so, I changed both the plug and cop. Hisory back in December about 4000 miles ago did a complete change of plugs and cops. About two weeks ago after a 800 mile trip to the mountains and the car ran great. Then, last Monday night on the way home from work the CEL came on? Went to Advance Auto and got code P0304 - misfire in no 4 cylinder, again!. So, last weekend I changed COP and plug in no 4, made sure the spring was makng contact and applied dielectirc grease like before. Also, checked and cleaned all contacts to all of the fuel injectors and applied dielectric grease to contacts. Now, after driving about 250 miles and coming home tonight the darn CEL comes on AGAIN! Go to Advance Auto and no 4 cylinder is the culprit!! Again!! I'm totaly stumped. Any good sugestions? I'm at a loss here? Thanks again!
 
damn dud sucks but change the coils and spark plugs and also be prepared for a cats code p420 because when you get a misfire it messes up your cats which cost alot
 
Was the plug or coil wet? Maybe the gasket is leaking oil. Possible injector is going bad.
 
oskiny said:
damn dud sucks but change the coils and spark plugs and also be prepared for a cats code p420 because when you get a misfire it messes up your cats which cost alot
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So, after all I've done I should change all the plugs & coils again? The car is running fine. I'm really stumped here! I didn't want to just start changing everything again and not know the actual cause but, understand if I might need a "new" baseline to determine what the heck is going on! But, geez only have 4,000 miles on all new parts! LOL.. Thanks!
 
cmack said:
Was the plug or coil wet? Maybe the gasket is leaking oil. Possible injector is going bad.
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Nope! All dry. I did double check that. FYI. I replaced the vcgs in December and also did all the plugs & cops. Now, here I am doing another plug & cop on no 4! Really stumped here?? Thanks for the advice.
 
IIRC someone on here, it might have been joegr, said that the computer doesn't alway recognize which cop if failing and will some times tell you the wrong one, so yes i would recommened replacing them all and see what happens after that
 
I have the same code. (v6 though) I'm experiencing occasional misfires at idle and under high load situations. My problem I've experienced several times and never had a code set until this week.

Here's some history.

After I bought the car it developed the miss. I fixed it(so i though) by replacing the spark plugs. It came back a few weeks later.
I replaced the PCV valve, elbow, and VCGs and found a cracked insulator on the (if I have the cylinders right) #4 cylinder.
I replaced the plug and everything was good for a week or two. I figured it was coils so I bought ebay coils and this fixed the problem for about a week (this was two months ago, third time taking the intake off for those counting, I'm a pro now and can do it in about an hour) then it came back.
I'm frustrated by this but keep driving the car daily because I've been working 7 days a week for the last 6 weeks and it's fine under light throttle.

I'm thinking it could be several things.
1. Spark plug bad again
2. New cheapo coils failing
3. Fuel pressure problem
4. Bad fuel injector

IIRC the #4 cylinder is the drivers side front but the problem is I read that the ford ECU guesses which cylinder is misfiring and it might not even be that one.
 
Mechanicboy said:
That was possible problem number 3... or pressure regulator not working correctly.
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The LS doesn't have a return flow fuel system, and so it doesn't really have a fuel pressure regulator. It does have a fuel pressure (relative to manifold vacuum) sensor. The PCM reads the fuel pressure, and sends commands to the REM to speed up or slow down the fuel pump as needed to maintain the correct pressure.
 
I thought that it was a returnless system but I'm not sure how to check whether a sensor or something else is bad. How do I know if the sensor is bad or it's a fuel pump? Also there is what looks like a pressure regulator on the fuel line going to the fuel injectors, what's that?
 
Connect a scan tool and look at the real-time fuel pressure reading. Compare that to a test gauge on the pressure test port.
 
joegr said:
Connect a scan tool and look at the real-time fuel pressure reading. Compare that to a test gauge on the pressure test port.
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Sounds good to me. The only problem is that my problem is intermittent so I'd have to leave the test equipment hooked up for a day or more. For instance yesterday once she warmed up she ran fine and I got her to 140MPH in 98 degree F heat with ease. I felt no engine troubles at all. I'm surprised on how well this car pulls on the top end, I think she'll do 150+ once I tune her.
 
bearsfan39 said:
i looked up the thread and it was actually your thread.....

http://www.lincolnvscadillac.com/showthread.php?t=66953

so did you actually check all the plugs and cop's or just say that.......
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Yes, I did change all the plugs & cops and no.4 keps comiing up bad. I also cleaned & checked all of the fuel injector plugs. So, I guess I'll be changing all of the plugs & cops again? I read that the PCM may not know which cylinder is actually causing the problem? So, the code reader is not reliable? Only thing left to do is shot gun and change everything?? Wow!! Can anyone recommend a good source on the web for reliable cops? The ones that I had gotten from global-automotive have turned ou to be junk! Thanks again!!
 
Dukernc said:
Yes, I did change all the plugs & cops and no.4 keps comiing up bad. I also cleaned & checked all of the fuel injector plugs. So, I guess I'll be changing all of the plugs & cops again? I read that the PCM may not know which cylinder is actually causing the problem? So, the code reader is not reliable? Only thing left to do is shot gun and change everything?? Wow!! Can anyone recommend a good source on the web for reliable cops? The ones that I had gotten from global-automotive have turned ou to be junk! Thanks again!!
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On the v8 it should be pretty easy to ohm check the injectors so I would suggest that first. It's harder for me because I have to tear the intake off to check mine.
 
Mechanicboy said:
On the v8 it should be pretty easy to ohm check the injectors so I would suggest that first. It's harder for me because I have to tear the intake off to check mine.
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Unfortunately, knowing that the coil on the injector is okay still does not verify that the injector is working. It could be stuck or clogged. Those two conditions are more common than an open or shorted coil.
 
Joegr,
Thanks for the information. I've since added some concentrated injector cleaner and a couple tanks of 93+ octane and so far no CEL issues! I've got my fingers and toes crossed! Thanks again!! :wrench
 
joegr, what is a way to find out which injector/s is not working properly? I really don't want to replace all 8 of them ($700) :eek:
thanks
 
JaredLS said:
joegr, what is a way to find out which injector/s is not working properly? I really don't want to replace all 8 of them ($700) :eek:
thanks
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Remove them, feed in pressurized fuel, apply current, and look at the resulting spray. There may be other ways, but that's the one I know of.
 
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