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6Bucs, Ford Senior Master
Category: Ford
Satisfied Customers: 889
Experience:  Ford senior master tech, 18 years experience.
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I've got a misfire on cylinder 3 (p0303) and a too lean on

Customer Question

I've got a misfire on cylinder 3 (p0303) and a too lean on bank one (p0171) on my 2006 F250 with 188K miles. The vehicle runs roughly both in idle and while running but it constantly fluctuates and will run smoothly for a second or more and then revert back to running roughly.
I've already swapped out the spark plug, coil, and fuel injector with components from other cylinders but the misfire does not follow any of the components. I put a light up spark plug tester on the plug #3 and it blinked consistently and steadily. I just did a compression test using the harbor freight quick-connect compression tester (#95187) which supposedly gives low readings and I got a reading of ~148psi on a cold engine.
I also sprayed some water around the outside perimeter (but not inside perimeter because it is too inaccessible) of the intake manifold since someone suggested that but it didn't disturb how the engine runs like it's supposed to if I have an intake manifold leak.
I sprayed starter fluid around the intake and nothing happened. I also put a noid light on the fuel injector plug and it blinked regularly like it's supposed to.
I should also mention that the misfire happens less when the engine is cold and gets much worse as the engine warms up.
FYI, when I first got this vehicle, it had numerous error codes.
P0011 - camshaft 1 timing over advanced
P0012 - camshaft 1 timing over retarded
P0021 - camshaft 2 timing over advanced
p0300 - random multiple cylinder misfires
P0303 - cylinder 3 misfire
P0304 - cylinder 4 misfire
P0340 - camshaft position sensor 1
P0345 - camshaft position sensor 2
P0430 - catalyst efficiency below threshold
To fix these errors I've done a lot of work so far. I cleaned up all the plugs and coils - some of which were actually rusty and I think a coolant line was leaking onto coils 3 & 4. Installed new camshaft sensors. Swapped vct solenoids and found that the error codes followed vct #1. I've ordered a new vct solenoid but am still waiting for delivery. The catalytic converer is no doubt shot from burning off too much unburned fuel but that's not important.
Here is a picture I took from my phone based OBD scanner while in park with a warm engine. You can the little surges in fuel and fluctuations in RPM. I'm not sure if those little surges are due to the cylinder finally firing or if there is another cylinder that's stuck open sometimes.
So if you could provide me any help with this problem, I would greatly appreciate it.
Submitted: 1 year ago.
Category: Ford
Expert:  HDGENE replied 1 year ago.

Ok does the engine smooth out while driving and only run rough at idle?

Customer: replied 1 year ago.
It runs rough when driving too. In fact, I get a flashing check engine light.
Expert:  HDGENE replied 1 year ago.

Ok and you have injector pulse and spark on that cylinder, You mentioned compression testing, did you only test the one cylinder or the whole bank/same side?

Customer: replied 1 year ago.
The cel stops flashing when idle so it probably is worse when running. It's more likely to flash when driving fast on the highway. I have limited engine power then too and can't go much faster than 55mph.
Customer: replied 1 year ago.
I only tested the one cylinder.
Expert:  HDGENE replied 1 year ago.

Ok, need to test compression on the one side to make sure cylinder number 3 isnt low, you should have no more than 10% difference inbetween cylinders or it will misfire, these engines are known for valvetrain issues as well as phaser issues with the 0012 and 0022 codes. make sure base compression is goo or it can indicate an issue with a worn intake or exhaust valve or worn rocker arm/camshaft lobe.

Customer: replied 1 year ago.
I will go test compression on the other bank but I can already tell you right now that compression is nearly ideal for cylinder 3. I have done some calculations for adiabatic comression of air just now ( based upon the cylinder displacement, air temperature at time of measurement (~40F) and the internal volume of the compression tester hose line. The ideal psi calculation I got for cylinder 3 is nearly the same as my measured value.Also, I disagree that a mere 10% variance would be enough to cause a misfire. It would usually take more than that.
Customer: replied 1 year ago.
i.e., the variance is already less than 10% from the theoretical ideal.
Expert:  HDGENE replied 1 year ago.


Customer: replied 1 year ago.
Ok, I've tested cylinder 5 which is on a different bank. It's compression was 125 psi.
Expert:  HDGENE replied 1 year ago.

Ok first when testing compression you want to check it when the engine is hot at normal operating temperature. If there might be an issue with engine timing you need to test compression on all cylinders since you have codes for vct timing issues

Customer: replied 1 year ago.
Look, I did the compression test. Do you have any ideas or not about the misfire?
Expert:  HDGENE replied 1 year ago.

You tested 2 cylinders out of 8 when cold. that is not an accurate test. I will opt out and seeif someone else can assist you.

Customer: replied 1 year ago.
Only one cylinder is misfiring so why would it be necessary to compression test all 8 cylinders? I tested the one and tested one other for reference as you requested originally to begin with.
Expert:  6Bucs replied 1 year ago.

Hello, different expert here. My name is***** you tell me which engine is in your truck?

Customer: replied 1 year ago.
The 5.4L 3 valve gasoline.
Customer: replied 1 year ago.
Customer: replied 1 year ago.
I have an endoscope, btw.
Expert:  6Bucs replied 1 year ago.

It's common on this engine for an intake valve spring to break, or a roller rocker to seize and wear out. There are 2 intake valves per cylinder, so it won't show up on a compression test. This may show up on a running compression test. Remove the shcraader valve on the compression tester hose and check compression on that cylinder while the engine is running. You should see half of what the manual compression was, roughly 70 psi. Less than that indicates a problem. It may be necessary to remove the valve cover to inspect the rockers and valve spring, as there isn't enough room to inspect through the oil filler neck on the valve cover back to cylinder #3.

Customer: replied 1 year ago.
I have tested the cylinder while running and warm like you asked for.Cylinder 3 showed 40psi while hot and running. 125psi while dry cranking and hot.I also tested cylinder 6 for comparison. It showed 50psi hot. 120psi cold. 120psi while dry cranking and hot.Also, recall that I was getting timing over advanced and timing over retarded on bank one previously and swapped vct solenoids between banks 1 & 2. The timing problems follewed solenoid 1 so I ordered a new solenoid which I installed yesterday.Yesterday, I changed the oil & filter for the first time since purchasing this truck. The old oil didn't smell much at all. The new oil was 5w20 as ford recommends.After the oil change, the truck ran worse. After about 20 minutes of driving, I got the cylinder 4 misfire again which I had thought I had eliminated before. Also I got the code for multiple random misfires. I also got the timing over retarded and over advanced codes again on bank one even though bank one was running using the vct solenoid that was originally on bank 2 which didn't show a problem before. Bank 2 did not get any codes.I was suspecting that I might get problems after changing the oil because a lot of people say that the thin 5w20 oil doesn't provide enough oil pressure in an old 5.4l engine to the variable cam timing system. I wanted to take off the oil pan to check out the oil pump but was unable to do so because I parts of the frame crossmember were blocking my access to some of the oil pan bolts. Some people had said the oil pump often starts failing or is inadequately tensioned on this vehicle when old.Would it be useful to try to see the valves with the endoscope using the fuel injector port or is that not possible?
Expert:  6Bucs replied 1 year ago.

You can look at the valves and seats through the spark plug hole with the scope. You may or may not see anything there.

There is a misfire on cylinder #4 now?

Ok, so for the timing issues, typically what happens is the phasers do not receive sufficient engine oil pressure to run them. You need a minimum 25 psi at hot idle of base oil pressure. What we often see, especially at that mileage is wear in the cylinder heads due to insufficient base oil pressure, either from a failed oil pump or excessive lateral crankshaft endplay. At this point, I would recommend removing the passenger side valve cover. You can look at the valve springs and roller rockers on cylinder 3 and 4. Remove the camshaft journal caps one at a time. There are no bearings in the cam journals, as they ride right in the cylinder head. Look for grooves worn in the cylinder head and camshafts from lack of oil pressure. If there is wear there, the cylinder head and camshaft will need to be replaced.


Customer: replied 1 year ago.
there is a misfire on #4 now. The code for it came up. However, it's not consistent. I switched the oil to 10w-40 plus some 85-90 gear oil and that misfire went away.However, I wanted to report on the additional info I have found out.Investigating the valves is a good idea but I suspected that something was wrong based on the fact that I was able to pull the fuel injector plug with no effect as I previously reported.I thought that maybe the noid test was wrong for some reason since the plug pulling test was contradicting it. I watched some videos online of other people using noid tests and I noticed that their noid lights were much brighter than mine despite the noid module itself looking the same as mine. I tested the noid light on my other vehicle, a Subaru and it was brighter on it but still not very bright.I decided to put a multi meter on the fuel injector plugs and see what that would show. I was suspecting that there was no fuel injector pulse despite the boid light having shown otherwise.I used a cheap harbor freight multimeter. I don't have an oscilloscope available.For the subaru, I was getting readings of 0.5v dc, 0.9v acFor the ford I got:
#3 cylinder - 12vdc 0vac.
#5 cylinder (for reference) - 12.5vdc, 26.8v ac.The #3 cylinder was not getting a pulse. I don't understand how the noid light was able to blink on it without any ac current going through it.I ordered a new computer for the ford and am waiting for it to arrive at this point.I will also be changing out the phasers soon as well.
Expert:  6Bucs replied 1 year ago.

Alright, let me know what happens. When the valve covers are off, make sure to remove a couple of the cam journal caps to look for wear. If there are grooved worn in the journals that you can feel with your fingernail this indicates an oil pressure problem.


Customer: replied 1 year ago.
I got the new computer a while ago. The misfire problem is gone now. There is still a problem with the engine being too lean on bank 1. I've been wanting to change the cam phasers but it's too cold to work outside now and the vehicle is too big to fit into my garage so I'm kinda stuck.