3.0 Misfire

My 2005 Ranger with a 3.0 has a misfire, P0303. When the engine is cold it starts up and runs great, after I drive it a while and get into stop and go traffic it has a miss and eventually the check engine light comes on.

So far I have replaced the following items:

Fuel pump and filter

Coil pack ( twice to make sure )

Plugs and wires

# 3 injector

Crankshaft position sensor

Throttle body gasket

Plenum gaskets

PCV valve

Cleaned MAF sensor

Spark tested # 3

Checked injector wiring harness with a noid light

Compression test and # 3 is very close to the same as other cylinders.

Cleared the engine control computer.


The PCV valve was hung open and completely worn out, I smoke tested it and I had a bad vacuum leak at the throttle body gasket.

After replacing the PCV and throttle body gaskets it runs better but after driving 50 miles it starts idling rough and eventually I get the P0303 engine code telling me that # 3 cylinder is misfiring.

Could it be weak valve springs on # 3?

 

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About the only thing you haven't replaced is the O2 sensor or the CAT. You said the compression was "very close" to the other cylinders, so I wouldn't think a valve spring is at fault.

 

I had trouble with the idle on my 4 cyl Ranger. I cleaned the MAF a couple times . I even bought the official MAF cleaner.
I finally had the chance to put my buddies MAF on my to trouble shoot. What do you know fixed it right away. I think it
was $60.00 or so to buy one. The fact that you are getting a specific cylinder code seems like it should mean something.
A weak spring would be weak all the time. Keep us posted this one is interesting.

 

Any code originates from a sensor detecting something's not right with whatever it is the sensor is monitoring.
When its not the exact thing that the sensor monitors, the problem is something associated with that part, affecting it in a way so as to cause a code....what's got me is....what is "associated" with Cylinder #3 that would do that?
Well, you did find some gasket leaks in the intake system, could there be more?
Does the intake split in half like the 4 cylinder engines do?
...things to look at.
Another thing that just hit me....cracked head, at the spark plug hole, thus misfire via insufficient grounding. That one's a reach, I'll admit, but I've heard that happening before.


Dean

 

I cleared the PCM and separated the catalytic converter from the exhaust pipe with a long socket to see if it was stopped up, it ran good then p0303 came up. I also put a new oxygen sensor on that side and cleared the PCM again and after driving down the road the same code came back.

It runs perfect when cold but when it warms up and the misfire starts it runs terrible.

 

I just read this on a forum that is called Diagnosing Ford Misfires


Many techs have wondered why on some Fords the Check Engine light does not come on right away when a misfire is present. This is primarily due to the misfire count not exceeding the limit. But there’s another way Ford protects the catalytic converter during misfire conditions. The misfire section of the OBD II document explains that if the PCM determines a cylinder is misfiring, the fuel injector can be turned off to protect the catalyst from damage. Once the fuel injector is turned off, the cylinder is now basically an air pump, which reduces the potential for catalyst failure.

 

I read this too, never knew this.

The Fuel Tank level must be above 15% for misfire monitor operation. It’s not uncommon to be working on a vehicle that’s low on fuel, but if the fuel level is less than 15%, misfire monitoring is suspended

 

You may be right, a friend of mine bought a F250 and brought it over for me to look at because it had a misfire. I scanned it and found the cylinder and pulled the plug, the plug looked fine, I got some anti seize and was going to put the plug back in and felt the threads in the hole and part of the threads were gone. Some idiot had pulled the plugs out hot and the threads came out with the old plug. He ended up having to buy a head. I bought my Ranger new and I have done all the maintenance so I know that my threads are ok but like you say, I may have a crack. Tomorrow I plan on putting # 3 on TDC and pulling the plug and smoke test it again. See if any smoke comes out of the plug hole.

 

...and just so we have it in writing, after you changed those gaskets, you found no other vacuum leaks, right?

 

I smoke tested it twice and no vacuum leaks, it only misses and shakes at low RPM at 1000 it runs great. the lower the RPM the worse it runs. I may be wrong but I think if it was a burnt valve it would run bad all the time. I just took it out and drove it 100 mph for about 5 miles and it ran great. I cleaned the camshaft sensor today, the MAF sensor (again) and the idle air control valve.
I didn't have a new rubber gasket for the idle air control valve so I cleaned the old one and turned it over. I live 35 miles from the nearest parts store. It is not leaking.

 

Not a burnt valve, but a cracked head....remember?...

This one is definitely a brain teaser. Seems like you've checked everything.

 

hi folks ==just a thought from an old guy =years back cam lobes were soft in fords SO I'm wondering if a lobe has wore slightly allowing miss fire at slower rpm and higher speeds the lobe is still able to lift valve high enough to work ok with that extra centrifugal force plus the movement of the valve ==maybe check valve lift by rotating manually with plugs out ===just a wild thought ===after re -reading your problem a cold engine will run richer so again this may be ok to fire cylinder and after warm and leaner fuel mixture valve wont allow enough fuel to fire cylinder ==good luck ==

 

Funny you write that, because if you ask a Ford guy, its the Chevy's that have soft cams. HaHaHa!

 

hi there =well a co -worker had an older ford and he had the problem with cam lobes ,, we found out after some research as to why he had this misfire=this occurred in a older v8 -and the car had ''FORD ' on the hood emblem, so must be a ford ??right ??

 

My dad had a '53 Mercury with a 255 in it. When I was a kid, he'd tell me never run a regular engine on Sunoco 260 gasoline, because that's how he burnt the valves in that car.
Years later, after diesel school, I got a better handle on how engines worked and repair techniques involved.
With the old flatheads, the lifters were just a solid block of metal and you ground one end down until you reached the specified clearance for the valve.
Turns out, dad didn't grind down the lifters enough and they didn't let the valves completely seat when closed.
Bingo! burnt valves.
Granted, my father was a master technician and had years and years of experience in automotive, marine and industrial engines and drivetrains. When he passed away, the world really did lose a treasure.
However, this happened many years before. I guess that was one to learn from.
..."Sunoco 260 "...good one, dad. =D

 

hi dean =the ford V8 i was referring to was a 1956 ford over head valve =soft cam lobe problem

 

Sorry, your comments reminded me of that story.
So it actually was a Ford engine?
...let's see, if memory serves, that should've been a Y-block.
272 by rights, but Mercury had a 256 at the time, too and that would probably fit, as well.


Dean

 

no apology dean -thanks anyway=i couldn't remember the displacement-but-272-Y block would be it....after stan reeves tried all the fixes I just thought of that problem years ago and chirped in =I hope he found a solution to the mis-fire =If i recall right ,back then cams were made off shore and did come back softer than specs,in some cases =thanks Dean for the info you sent I appreciate it = I'm from the old
''dwell angle'' days''' when electronic ignition was still out in space =take care

 

Not trying to be "Mr. Know-it-all" here, but most memorable of the old Y blocks from the 1950's and early 1960's were 292 cubic inches. The "Thunderbird Special" used the same block, but was a larger bore and stroke yielding 312 cubic inches. Loved those old engines; they had a sound all their own!

 

...and the supercharged 312's went like stink!