4.0 Missfire, perplexed...

[ABNRanger]

Hello and thanks for reading! I've browsed the forums and have seen about 16 or so missfire situations on the 4.0L V6 engines and I'm about at wits end as to why mine keeps doing it. I first noticed it when i would pull up to a stop sign, the truck would almost lurch back and forth. I replaced the plugs and wires as well as filter, oil and tranny fluid thinking it could be that. It still did it. I replaced the plugs again, the coil pack and the #2 Injector (BTW, it threw a p0302, cylinder #2 Missfire code and CEL). With the injector changed, it stoped for about 30 mins. Then started again. I've rechecked everything and still nothing comes to mind. I've heard about the possibility of it being a leaky intake man, but wouldn't that cause it to miss in more then one cylinder? Any help will be greatly appreciated. Also, I've cleaned the MAF and ran injector cleaner through it about 4 times.

 

[ABNRanger]

So, I also replaced the lower intake gasket today as well as the friggin manifold gaskets. The kit i bought came with a 1 inch circular gasket I didn't find a place to put so that's in the back of my truck. So, if maybe that helps anyone with a possible cause let me know. Tomorrow I'm replacing the O2 sensors. We'll see where it goes from there. Wouldn't it throw an O2 sensor code though? Again, thanks!

 

[Little Egypt]

Mine didn't throw an O2 code - it was just saying lean fuel mix. My problem ended up being a combination of bad lower intake manifold gasket and bad O2 sensors.

Cheers,
Aaron

 

[ABNRanger]

Mine keeps saying cylinder 2 miss. BUT I changed out the lower intake man. gasket and the CEL went away. BUT it's still missing to the point I can feel it at warm idle. O2 sensors the culprit?

 

[ABNRanger]

Okay well, I bought 2 new O2 sensors today and am about to change them out. If anyone else has any idea as to what could be causing this please let me know. Thanks again!

 

[KELLY88]

When it comes down to a situation like this it's usually a better idea to pay a shop to hook up the computer and tell you exactly where the problem lies. It ends up being cheaper than spending all that money on parts that you THINK might be bad.

 

[ABNRanger]

You're not lying. I just replaced the 02's and NOTHING CHANGED. Also, did a compression test. 1-115 2-90 3-110 4-115 5-115 6-115. I'm going to do a wet test, depending on the results of that, I'm going to have to take it to Ford. I asked a friend about that though and he said the only thing they're going to do is run a scan. Which will give me the same P0302 code I've been getting. Then tell me I need to fix everything I already have and charge me millions for it. Maybe they do have a magic, "this is EXACTLY the cause for your missfire, sir" machine. In which case would kick ass. But I'd really hate to spend 100$ for them to do nothing more then what I've done ya know? If the wet test fails tomorrow then I'll definetly take it to ford. Thank you for the response!

 

[Little Egypt]

Yeah, when I took mine to ford, they told me I had a lean fuel mix code. I have a code scanner and already knew that was the code. You can get the codes pulled from any parts store for free too. The only reason they told me it was the O2 sensor was because that was the only thing I hadn't changed (I gave them a list of everything I had done over the past year). They were right, but it was only a guess on their part - they kept saying "probably".

Ford doesn't have any magic machines that tell you exactly what's wrong with your truck. They have the same machines as everyone else - they just charge more. Since they specialize in ford vehicles, it's possible they've seen your particular problem before, but it's just as probable that the small shop down the street has seen that problem too.

Cheers,
Aaron