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Old 10-31-2008, 08:02 PM   #1
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Default 4.6 Misfire

Thread indicates 5.0 but its actually a 4.6....sorry
1997 F150 4.6 started missing. Codes issued were a 304 and 308 (cylinder 4 and 8 miss) plus got a code 401 (EGR low flow). Changed plugs and wires (Autolites) and still getting code 308 (cyl 8 miss). Replaced coil pack for even numbered cylinders still missing. This miss started suddenly. Starting to think it maybe mechanical rather than electrical. The code 401 is also still with me.....any suggestions. Could a vacuum leak be suspect? Fuel filter or possibly injectors? Hate replacing everything.

Last edited by whitecrystal1; 11-02-2008 at 05:55 PM. Reason: To correct the title
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Old 10-31-2008, 08:08 PM   #2
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ima replace all my plugs boots coils and injectors this weekend (97' F250 5.4L) kinda got the same problem missing wont throw codes but it has in the past. my old mechanic did something to my EGR valve a while back (didnt say what) it made the truck run better but the check engine light wouldnt go off so i had to get him to undo it to go through emissions controls. ill let you know on the injectors if its any help
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Old 11-01-2008, 02:53 PM   #3
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I have the same issue with my 2001 5.4 with 63K miles, but only misfires intermittantly when engine is hot and with applying slight accleration. I also have no check engine light. The misfire finally showed up on cyl 5 & 7. Had the plugs replaced, the mechanic put in Autolights problem got worse. Took the truck back they installed Motorcraft, which someone on this site recommneded, also replaced all the boots. Problem is still there but truck runs better and it takes more time (gets hotter) for it to show up. Also had the injectors checked, all good, have dumped heet in the gas tank thinking maybe water in the gas, and changed fuel filter. Don't know what to check next. May go for the EGR valve/sensor.
Please write back if you find anything that works.
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Old 11-02-2008, 12:31 AM   #4
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Tested DPFE and replaced both coil packs. Still got 308 and 401 codes.
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Old 11-02-2008, 05:41 PM   #5
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i had a "DPFE" censor go bad a while back i got it replaced and it made a little difference but i just changed all my plugs (put iridium plugs back in) boots and coil packs and also replaced all the injectors (Ford Racing injectors you can find a whole set of 8 pretty cheap pretty much like stock) and yeah it helped a bit but the engine still has a slight miss a idle im kinda lost for why but it drives fine so i dont know what it is i run high test gas too that also helps (hypertech programer) but even before i installed that i ran 89 and if i ran on 89 for long periods of time it would help but still didnt totally cure the situation but then again its a 97' so i dont know how much i can expect out of it
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Old 11-22-2008, 10:07 AM   #6
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Problem solved. NEW MOTOR. Got into the motor and all was bad news. Cylinder 8 had 20 lbs. compression. Removed head and of course head gasket blown. Not surprised, could smell antifreeze in exhaust. Also when valve cover removed there were signs of water (light brown residue). Number 8 hole shot. Found 97 4.6L, 81K miles to be installed soon. Thanx to all for suggestions.
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Old 11-22-2008, 10:07 AM
 
 
 
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