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Dieseljunky2, Ford Mechanic
Category: Ford
Satisfied Customers: 3946
Experience:  ASE Certified, Ford Certified, Cummins Certified, & 20+ years in field experience
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Explorer sport trac: P0304, cylinder 4 misfire..runs fine..rough idle

Resolved Question:

03 explorer sport trac - P0304, cylinder 4 misfire, changed plugs, wires, coil pack and intake manifold gaskets. No luck. Pressure test is okay, runs fine just rough idle and the CEL always on??
Submitted: 7 years ago.
Category: Ford
Expert:  Dieseljunky2 replied 7 years ago.
Take the fuel injector for cylinder 4 and put it in cylinder 5 position and injector 5 moved to cylinder 4. The misfire will probably move to cylinder 5. If this happens replace the fuel injector that was in position4, now in position 5.
Customer: replied 7 years ago.
Yep, tried that too, misfire did not move from cylinder 4. I was thinking timing, once in a while when turning off the car it will continue to roll over as if the timing was off however timing is not adjustable right?? There is also no PCV on these vehicles is there?? I can't locate one. If not timing could it be the PCM?? I have no coolant loss to indicate a head gasket. A cylinder compression test seems fine??
Expert:  Dieseljunky2 replied 7 years ago.
Hook a noid light up to the injector 4 spot and test run it and see if it blinks.
Customer: replied 7 years ago.
I will try that but I believe the injector signal has been confirm. As I mentioned it runs fine through accelaration and drives perfect, just really poor idle. Could it be the PCM or timing chain?? The truck has just over 100K miles on it. The valve cover has been pulled of to confirm no broken valve spring or damage to the valves. I removed the EGR and IAC and cleaned both of those. I have also put a few can of injector cleaner through it and while I had the intake manifold off I sprayed the heck out of the valves and noticed that the cylinder 4 valve was holding liquid for more than an hour or so while I cleaned and installed the new gaskets.
Expert:  Dieseljunky2 replied 7 years ago.
Have you tried wiggling the harness around while it is running to see if you can make it misfire? Especially around the pcm connector. Timing chain would cause problems on the entire side that it is on. It is very possible that the injector driver for cylinder 4 is weak. I have also seen an ignition coil that was weak on one cylinder cause a miss only at low speed. This was checked by using a pair of insulated pliers and holding the plug wire near its position and slowly moving it away from the coil and watching the arc for color and how far the spark would jump. Then compared it to all the other coil towers.
Customer: replied 7 years ago.
I have replaced the coil pack with no change, these coil packs fire two cylinders with 1 coil right, in this case 3 and 4 are on the same coil. I have removed the connection from the PCM to check for damage but didn't see anything. The idle is so rough I don't know how I would notice a misfire. When I changed the intake manifold gaskets it ran better for a week or so then seemed to run worse. The CEL remained off for more than a week of daily driving, the longest since I have owned it, the idle wasn't perfect but noticably better?? Currently if I reset the codes the CEL will stay off for no more than 2 days. Changing the gaskets was the last thing I tried. I was going to have a look to see if any of the fasteners had backed off but I did torque them all down to the appropriate spec. I will have another look this evening, I have been after this problem for 3+ months.
Expert:  Dieseljunky2 replied 7 years ago.
When you say you changed the intake gaskets, Did you change the upper and lower gaskets?
Customer: replied 7 years ago.

Upper and lower, this is the SOHC model with the molded plastic intake, I thought this set-up only had the oval o-ring type gaskets?? These seals go directly to the heads? I am working from a Hanes manual which isn't all that great!

What about the PCV, there isn't one on this engine is there??

Expert:  Dieseljunky2 replied 7 years ago.

Had a brain fart there, you are correct on thhis model there is only a one piece intake. Did your bolts have the rubber grommets on the bolts, if so, did you change them also? Here is the pcv system.

Positive Crankcase Ventilation (PCV) Valve

  1. Remove the components in the order indicated.

Part 1 Of 2

Part 2 Of 2

  1. To install, reverse the removal procedure.
Customer: replied 7 years ago.

On my system I have a hose connected from the air intake tube (just after the filter) to the passenger side valve cover and a strange connection on the back side of drivers side valve cover which has a larger and small hose coming off of it, the drivers side one doesn't seem to come out, neither of which go to or have a PCV connected. When I went to my local parts supplier asking for one they didn't carry one. My assumption to date is that there wasn't one???

I am almost done here and have to leave, how do I continue this with you once I check out a couple of things??

Expert:  Dieseljunky2 replied 7 years ago.
Reply to this message. The pcv is on the driver's side in the valve cover. It is only available from ford. It twists in like you are trying to screw it in. Pull out on it with a counter-clockwise turn while pulling out.
Customer: replied 7 years ago.
I did purchase a PVC and replace it, no change. As for the rubber grommets on the intake fasteners, no I did not change those when I replaced the gaskets.
Expert:  Dieseljunky2 replied 7 years ago.
I would replace those, they are the main cause of vacuum leaks on the gaskets, because the don't put enough pressure downward on the manifold to hold the seal.
Customer: replied 7 years ago.

I will try that I guess, I am running out of options!! I have had it to a ford dealer (they confirmed injectors and valve spring) and all they wanted to do was pull apart the engine, didn't make sense to me and they were proposing spending thousands of dollars. No engine noise, good pressure, no broken or damaged springs, no oil loss, no anti-freeze loss, no other options or opinions just this is what we want to do and this is what it will cost. Would you have any other ideas for me before I accept??

Expert:  Dieseljunky2 replied 7 years ago.
That is all I can think of. You have just about covered everything. The pcm will be all that is left after this. As far as an engine tear down, I would avoid that, it makes no sense.
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