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Old 02-04-2008, 10:01 PM   #1
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Default misfire cylinder 3 (4.6L)

I have a 98 F150 with a 4.6 with 134000 miles on it. On friday it started mising and set code PO303. I changed the plugs which were original, cleared the computer. Didn't drive it much this weekend but everything seemed fine until today. It started missing again and check engine light came on again. PO303 again! I bought a new coil pack, cleared the computer but within 6 miles it did it again. I brought it home and swapped #3 wire with #7 cleared the computer and took off hoping the problem would follow the wire. It misses a little and has a low idle which it also started doing when the problem first come up but doesn't set a code. I got my timing light out just to watch the flashes for a misfire but #3 seems fine but it seems all the cylinders are skipping a beat from time to time. Keep in mind the last time this timing light was used was abou 12 years ago. I"m confused on which way to go now. Tomorrow I'll get a tube off dieletric grease and see if that helps, any thoughts?
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Old 05-06-2008, 09:29 PM   #2
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Town Hound,

I had the same issue, except on cylinder #5. I even tried a new coil pack for the side that fires #5. What fixed it for me was replacing the injectors.

However, the truck ran flawlessly until about a month ago when we ran the tank really low (or it's just a coincidence), and it started missing again. I continue to get a P0304 code (Misfire on Cylinder #4), but I can't seem to fix it. Swapped coil packs, swapped injectors, ohmed out the plug wires, too. It runs great at first for a couple of miles, then starts missing. Occasionally it will clear itself and run smooth before starting the miss again. I would argue that it's a thermal issue; as the truck gets warm it starts to miss, but I also keep thinking it's somehow related to running the truck dry. I even replaced the fuel filter in case that was clogged.

Nick
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Old 05-31-2008, 11:15 AM   #3
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Default Another solution

http://www.f150forum.com/showthread....5445#post75445

(quick preview: water/humidity...)
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Old 05-31-2008, 09:21 PM   #4
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Quote:
Originally Posted by nicknels View Post
Town Hound,

I had the same issue, except on cylinder #5. I even tried a new coil pack for the side that fires #5. What fixed it for me was replacing the injectors.

However, the truck ran flawlessly until about a month ago when we ran the tank really low (or it's just a coincidence), and it started missing again. I continue to get a P0304 code (Misfire on Cylinder #4), but I can't seem to fix it. Swapped coil packs, swapped injectors, ohmed out the plug wires, too. It runs great at first for a couple of miles, then starts missing. Occasionally it will clear itself and run smooth before starting the miss again. I would argue that it's a thermal issue; as the truck gets warm it starts to miss, but I also keep thinking it's somehow related to running the truck dry. I even replaced the fuel filter in case that was clogged.

Nick
pull youre fuel pressure regulator apart and see if it is full of rust. I have seen a few that do this and the fuel pressure gets high and causes misfires. If you pull the snap ring it will come right out

towhound ,, I would try swapping coils side to side and see if it follows
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Old 06-01-2008, 02:18 AM   #5
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I ended up replacing the plug, which has fixed the problem so far. I recall seeing an issue on this forum about coolant leaking from the heater hoses right above the #4 plug hole, which heats up and causes the plug wire boot to lose contact with the plug, or something like that. When I pulled the plug out there was some kind of fluid residue on the outside of the plug, but it was hard to tell exactly what it was.

If it's a coolant leak problem, there are no obvious signs of that. I'm just glad the rig is running good now. FYI, I ran one and a half cans of Seafoam through the truck - some in the crankcase, some in the tank, and two applications to the intake (brake booster hose). I had no smoke whatsoever, but the engine does seem to run more smoothly now.

I will keep the regulator idea in mind in case this happens again.

Nick

Last edited by nicknels; 06-01-2008 at 02:19 AM. Reason: added info
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Old 01-20-2012, 12:48 PM   #6
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ihave the same problem on cylinder 1 just did a full tune up still doin it switched plugs and wires still doin it so im gonna switch injectors hopefully that works
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Old 01-26-2012, 08:35 AM   #7
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I have a crown victoria with the same engine. it was idling rough and eventually through up a code it was P0303. The number 5 cylinder was misfiring and running lean.
*GET A COMPRESSION TEST DONE ON ALL CYLINDERS*
Because it wasnt just the #5 cylinder it was every cylinder on the left side of the engine but for some reason the OBD2 reader diddnt pop codes for all of that, just the #5. The timing chain guides (which are plastic by the way) broke on the left side. An easy fix then reset the timing and everything was fine.
Something else to consider before you start throwing more parts at it.
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Old 02-25-2012, 01:04 AM   #8
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I have a similar problem I have a cylinder 3 miss fire check engine light will flash sometime. The truck has its days when it runs great then sometimes you can feel a skip when stoped I have replaced the fuel injector, plugs, coil pack on that side, wired look Farley new just bought the truck and can't seem to get rid of the skip it's drivin me crazy and ideas? The intake is not leaking and don't seem to have a vac leak idles fine. I it's a 97 f150 with 230000 miles
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Old 02-25-2012, 05:29 AM   #9
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Try taking the injector out and cycle the key to get and dabree out of the fuel rail
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Old 03-07-2012, 10:07 PM   #10
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Okay I'll give it a shot the injector did look pretty nasty when I pulled it off
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Old 03-07-2012, 10:07 PM
 
 
 
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