Hi everybody, I'm totally stumped as I have done many things to try to remedy this dreaded code. After searching the vast interwebs for solutions it seems many others have not been able to fix this or they never posted their fix. When I drive the freeway I can feel the truck shudder and misfire when im in 4th and 5th gear then the light will come on after about 80 miles from reseting the ECU. Occasionally the CEL will flash which is alarming because I heard this is very damaging to the cats. Street driving is fine. Rock solid idle and I get about 15mpg( body lift, suspension lift, light bar, tubular bumper, and 33x12.50 tires)

Before this code it was throwing a CEL for EGR valve something or other. So I changed out the EGR solenoid, and DPFE sensor.

Other parts I have changed recently include:
Spark Plugs (NGK)
Wires (NGK)
New Coil
PCV Valve
fuel filter

Compression check has each cylinder coming out between 150-160psi.

I do notice im losing quite a bit of oil (1 qt every ~125miles). There is a tiny drop collecting at the bellhousing but its not puddling at all in the street. Also during the compression test I noticed there was some oil on the threads of spark plug #1. Not sure if thats relevant though.

I want to do a leak down test and see whats going on with the head but I dont have access to a air compressor. I'm debating on whether or not to take the intake off and switch the injectors from #6 to another one and see if the misfire moves to another cylinder.


Any suggestions would be greatly appreciated as this is my daily to get to school and Im currently unemployed so I cant afford a tech to check it out. Thank you.

 

Welcome to the forum

Yes, flashing CEL means bad mis-fire in progress, and computer would shut down #6 injector at that time to prevent unburned fuel from going out exhaust and into Cats

If you have tried a new spark plug in #6 and check firing order on coil pack
3 4
2 6
1 5
Front

5 6 4 side gets me every time, lol

Then I would test injector, not hard to do
All fuel injection computers have a Clear Flooded Engine routine
Ford(and most of the others) use this to enter Clear Flooded Engine

Turn key on(RUN)
Press gas pedal down to the floor(hold it DOWN) all the way
Turn key to START
Engine will crank but should not start or even fire

Fuel injectors are shut off but spark is still on

If engine starts you could have a leaking #6 injector, or a stretched throttle cable, google: Ranger throttle cable mod

So engine didn't start, which is good
Now that we know fuel injectors can be shut off, lets see if they are all working
(just FYI, is use this Clear Flooded Engine every morning when I cold start my 4.0l with 350k on it, I get oil pumped up to the top then release gas pedal for it to start so I don't get a dry start)

Now disconnect coil pack's 4 wire connector, so no spark
Crank the engine a few times, but don't push down on gas pedal

Pull out #5 and #6 spark plugs, both should be equally WET with fuel, if #6 is dry or drier, then fuel injector is clogged up, replace it

reconnect coil and start engine
Turn engine off
Do same test, no spark, and use Clear Flooded engine
Pull out #5 and #6, both should be dry, if #6 is wet then you have a leaking injector


Your compression is good, leak down test won't tell you anything more
But the loss of oil and #6 misfire could mean bad valve guide seal
#6 is at the back of engine so #6 valve guides are usually covered with oil
Intake vacuum can suck the oil down the valve stem where it is sucked into the cylinder and ends up fouling the spark plug over time
What did the old #6 spark plug look like?

Old test for failing valve guides was to go down a hill in a lower gear using the engine as the brake to slow you down, this creates very high Vacuum in the intake, so will really suck in the oil if guides are failing, then at bottom of the hill or after at least a minute or two of engine braking, step on the gas and watch for tell tale puff of black/grey smoke out the tail pipe from burning oil in the cylinders

 

Thanks RonD. I believe the firing order is correct since I made it a point to not fudge that up but ill check again. Cool trick with shutting off the injectors via holding the gas down. I tried it this morning on the way to school and it indeed keeps the engine from firing. Ill finish the rest of the diagnosis procedure when I have time this weekend and report the results.

Also CEL came back today after driving 50 miles. I notice the truck drives much better when the CEL is on. My guess is PCM removed cyl 6 from the picture as you mentioned and I'm running on just 5cylinders.

 

It may also be switching to Batch Fire injection when CEL is on
Batch fire on a V6 means PCM will open 3 injectors at the same time, and alternate with the other 3.
Usually ODD and EVEN
1, 3, 5
2, 4, 6

This is similar to throttle body injection, one step above a carburetor.

It keeps the intake full of air/fuel mix, like a carb did, and the intake valve that opens sucks what it needs in.

With Sequential injection you waste less fuel, but an individual injector issue can effect that one cylinder.

Most PCMs/engines run Batch Fire at cold start, and don't switch to Sequential until O2 sensors start to work, when they are at 650degF
This can be one reason people report "it runs good until it warms up a bit", but there are other reasons for that as well so not a definitive symptom for fuel injectors issue

 

Sorry for delayed post. School has kept me pretty tie up.

I tried your wet spark plug trick RonD and found that neither of the plugs were very wet. I compared cyl 6 (the offending cylinder) with cylinder 3(rear left). Cylinder 3 did seem to have more wetness on the threads of the plug than cyl 6. I would expect the wetness to be on the electrode itself? Would that be conclusive in digging in and replacing injector? I also found a steep downhill to see if my valve guides were fudged and there was no smoke to be seen at the bottom. Im stumped. I notice the CEL will periodically go away on its own but come back at the same hill of my commute everyday. Freeway speeds 60-70 on an uphill freeway ramp. This is what plug 6 looks like anyways.





During the spark plug comparison I did find spark plug number 1(front left cylinder) to be totally fouled and covered with oil on the threads. What would cause a plug to look so bad. It was really gritty. Curious as to why I wasn't getting a misfire code for this cylinder as well. Heres a picture.


cylinder 1 spark plug

Also is it common to leak oil from the headgasket in the rear of the engine by cylinder 3? I think its oil. I went ahead and tasted it (lol I know) and it wasnt sweet so Im assuming oil.




some leakage.



Residue. Left is the transmission and right is the block and where the oil filter mounts if I remember correctly.




better vantage point. green plug for reference



tried to stick my phone back there and see what it looks like behind engine.

 

#6 misfire codes can be mistaken, its a computer(well more a simple calculator), so garbage in garbage out

After seeing that picture I would focus on #1 for testing
That could be oil or over rich mix causing that build up, inside of that cylinder will look the same

Yes tips should be wet, you may have some oil on the threads, try cleaning threads before reinstalling spark plugs for the test

You can get some seepage from head gaskets, especially at rear lower corners, thats where the drains are for the oil from the valve train going back to oil pan, composite gaskets absorb oil and it can wick out to edge of gasket

Computer detects "misfire" by a cylinder not providing the same speed advance to the Crank as the other cylinders when engine is under load, also idling
There is a 35 tooth Tone Wheel on the Crank, Crank sensor detects each tooth as it passes.
The tone wheel has 36 teeth - 1 tooth, so a tooth every 10 degs for 360 deg full circle
The missing tooth denotes #1 piston at Top Dead Center(TDC)
Crank sensor pulses tells the computer the RPMs, and the millisecond timing increase if speed is added to crank by a cylinder firing, or if timing doesn't increase because cylinder misfired and didn't add speed.
On a V6 a cylinder fires every 120deg of crank rotation, so 3 cylinders fire every 360deg, 4-stroke engine so 2 RPMs = 1 full cycle for all 6 cylinders

#1 cylinder fires right after #6, so computer could be making a mistake, considering the condition of #1 and #6 spark plugs, but thats still a 120deg offset so its a long shot but not a no shot, lol

Because misfire only happens under heavier loads, going up hill, it could just be dirty injector
I would run a can of Seafoam, or similar injector cleaner, in the gas tank ans see if problem goes away after 1/2 tank
I do this once a year on all my fuel injected engines
Really helps my 1994 4.0l idle better, should probably do it to that engine more often, but I am cheap, lol

 

Its definitely oil as there is a large amount of it on the threads of the plug. Is there a seal or something that leads to the spark plug? Ive run two bottles of concentrated techron in the past ( 6 months ago?). Figured that would be adequate for injector cleaning but ill try again I suppose.

During the test I checked different plugs to compare wetness and none of the tips looked all that wet but they did smell of gas. I was expecting them to be drenched in gas? Is that a red flag in itself?

 

No, cold engine start is a Rich mix, Choke Mix, but won't drench the spark plugs

And the gas will evaporate fairly fast, even in cold engine, because compression warms it up

If you have another vehicle handy you could do a quick test just to compare, point of reference

The threads get oil from the outside, not from inside the cylinder, it can collect in the depression of the spark plug hole
Unburned fuel can get on the threads and it does look like oil because most of the hydrocarbons have evaporated from the heat, so precursor to the varnish left over after "gasoline" has evaporated

 

Update incase someone finds their truck having similar issues. I continued driving with the misfire issues. Ended up replacing both heads last week. Cylinder 1 valve had a hole burnt straight through it as shown below. Misfires have been gone since. Hope this helps someone.

 

hey Rond I was doing these tests too because I have a misfire in cylinder 6 too. I started with a misfire in 5 and 6 properly gapped my plugs and reinstalled and went down to only a misfire in number 6. I tested my coil pack and they were good as well as my wires which were just replaced. I am down to my injectors and used the clear flooded engine routine and it didn’t started but when I disconnect coil pack number 4 my engine still starts so I’m not really sure how to check my injectors from here without removing them.

 

You should do a Compression test first, before looking at injectors as the cause of misfire, P0306

Compression test should always be first, but spark plugs are easy enough to change so are often done first

Compression numbers are good or bad, not really a grey area because it is a mechanical number, so once the test is done you know for sure what to do next, pull the heads or check spark and fuel