4.6 V8 running bad - need help !

[aliomi2003]

Hi, I hope someone can help here
Got 2006 Explorer with 4.6 V8 engine and it started to run really badly. Check engine light came on, at times it flashes, then it stays on. Code is P0302. I did the following on cylinder 2: new ignition coil, new injector, new spark plugs (all 8), new fuel filter, cylinder compression checked OK, fuel pressure OK, power runs OK for both injector(s) and spark plug(s), no air leaks anywhere. The engine runs badly, it shudders really badly although intermittently, sometimes at idling runs OK, when I take the foot of the gas also runs OK. When accelerating, it revs up but does not “pull” right, when I try to keep it constant at, say 60+ MPH it once again does it badly. It first started some months ago with getting some "bumps" when holding steady at some higher speed, in time it started doing it more and more until now I can't drive it at all. It does start tho and most times appears to be running OK at idling. I’m really losing my patience, I love this truck but this is getting frustrating, anybody has any idea? The work I’ve done should eliminate the following:
- spark plugs
- ignition coil
- injector
- air leaks
- valves bent (got good compression)
- fuel pump (got fuel pressure and when I accelerate it does go .. to some degree)

Anybody can think of anything?

Thank you in advance

 

[MustangP51]

Welcome to the forum.

I would try swapping a coil from another cylinder that you know is firing properly to see if the misfire changes to another cylinder. I have had a DOA replacement coil send me on a wild goose chase once before.

Crank the engine for a moment or to with the plug removed from the cylinder (Grounded) to see if it is actually firing. This will eliminate any doubt of an ignition system problem.

If the ignition system is working properly, I would perform a leak down test on the cylinder, a leak down test can expose problems that a compression test may not.

 

[MustangP51]

One additional thing, Check to see if the fuel injector is getting the electrical pulse from the wiring harness.

 

[aliomi2003]

Thanks for replying.
1. Yes, both the spark plug and the injector do get electrical impulse, I checked that

2. I also swaped ignition coils with other cylinders, not to mention I tried 2 new ones on cylinder 2, still the same code came on (after clearing the code first) and still runs badly.

I guess I'll have to try the leak test on the cylinder but since the engine oscilates between running good for a little while, then goes bad makes me think that couldn't be the cause. I'll try it though

Thanks for the input

 

[MustangP51]

Were you able to check for the electrical pulses when you were having the problem? Something that is intermittent like that to me sounds like a wire is shorting out (maybe there is damaged insulation on a wire, water getting in a connection), bad connection somewhere, or worst case scenario the computer. You are correct this doesn't sound mechanical.

 

[rpenner54]

Vacuum Leak on the back side of the throttle body.

http://www.explorerforum.com/forums/showthread.php?t=254270
http://www.explorerforum.com/forums/showthread.php?t=217062

 

[aliomi2003]

.....

rpenner - I'll check for vacuum leaks although my mechanic friend had it for almost a week in his shop, he also looked for leaks; I don't mind checking everything two three times ... before selling my offspring to pay for what a dealer wants to diagnose and fix.

Mustang - indeed to me seems like this is electrical, less of a wire short since it does it too "consitent" but electric issue none of the less.

 

[Explorer_PL]

When I had my 4.6 shaking badly, before I replaced the sparkplugs which in my case were the problem, my mechanic mentioned that the intake manifold is prone to cracking. They would do some type of "smoke" test where they would seal the ends and see if it smokes at the seems where its glued together. Not sure if that is related to your problem, but just my 0.02 to help.
Good luck.

 

[MustangP51]

When I had my 4.6 shaking badly, before I replaced the sparkplugs which in my case were the problem, my mechanic mentioned that the intake manifold is prone to cracking. They would do some type of "smoke" test where they would seal the ends and see if it smokes at the seems where its glued together. Not sure if that is related to your problem, but just my 0.02 to help.
Good luck.

Its possible, a cracked intake manual would show low vacuum and he says that's within spec.

 

[aliomi2003]

Makes sense. Of course it's not easy to check for a cracked intake manifold, I will see if I find a way to check it without taking it out.
Thanks guys for all the suggestions, at least now I feel hope

 

[aliomi2003]

So, I finally got it fixed, or so I think, here's the funny story: Last week I thought I will give it another try so I started to loosen up the spark plugs on the opposite banks of cylinders, the driver side (code was P0302 = cyl # 2, passenger side). Took the wireconnectors off, loosen the spark plugs, I was gettggn ready to tear into it when a friend shows up. We started talkign and he asks me to take it, again, for a test ride, just so he hears it running. I put the connectors bak but I forgot to tighten the spark plugs back. Go for a ride, it rides rough but not worse than before. Being fed up, I gave up and the next day I'm taking it to Ford dealership for a diagnostic. At the end of the day they called me saying they fixed it. What the problem was in their opinion ... two loosen spark plugs on the driver side cylinder bank !!!!!!!! I told them what happen but they said that was the only thing wrong and they tested for 20 Mi. Paid $350 and the damned thing runs like a champ since - WTF???? Can someone explain to me why a code for misfiring cylinder # 2 got fixed by tighten two spark plugs on cylinders # 6 & 8 ? now if this isn't weird, what is? Again, almost a week later, the truck runs perfect, no stumbling, no check engine code, pulls strong ...
Thanks all for the input, I wish I had a clear resolution to my problem but in the end I'm happy this thing got somehow fixed.