I have a 03 F150 with a bi-fuel 5.4 engine an it has 195000 miles. I have had trouble for some time now with misfires. I bought the truck in october of 2011 with 125000 miles and replaced all the coils and spark plugs because it was misfiring badly will running on CNG. It was fine on gasoline and never had any codes. After I replaced the plugs and coils it ran fine on CNG and gasoline.
This summer 2013 it began missing badly at highway speeds only when running on CNG. If I accelerated the miss would go away until I was light on the throttle again.I checked the misfire count and found the bad cylinder and replaced a coil. Then a day later same thing on another cylinder. I swapped a coil from another cylinder and problem went away for a day. Eventually I chased the misfire around all the cylinders on the engine until I had ended up either replacing a spark plug or swapping a coil on all the cylinders. And I still had a misfire. It seemed to be worse on days with temperatures above 90 degrees. Eventually I got it to stop misfiring.

So now 5 months later I am back again with a misfire. This time it is misfiring on both gasoline and CNG and under any throttle conditions, except coasting. I have no codes. And the misfire monitor is sending me around the engine again. I have replaced a spark plug in two cylinders and swapped 4 coils.
I'm ready to buy all new coils, but I want to be sure that it is not a waste of money since the old ones only have 70000 miles on them.
Two days ago I had the misfire monitor saying #4 in the evening and the next day without me having done any work on it it was saying #6. Later that same day it said #7 and I still hadn't done anything other than drive the truck.
I checked the connections at the firewall on the drivers side with the three large plugs that are held in with a 10mm bolt, they looked fine, no corrosion or burnt pins. I checked the connection at the ACFM which also looks good. I will check the connection at the PCM in the next day or so.
Some other problems that may be contributing:
1. I occasionally get a U1262 code (scp fault)
2. Sometimes when I check the misfire monitor it only shows 7 cylinders, sometime 9 cylinders. I am using an Innova 3160 scanner.
3. I have either a leaking valve cover gasket or leaking head gasket, because I have oil dripping from the rear bottom corner of the passenger side cylinder head right above the exhaust pipe.

I'm sorry for this long post, I just wanted to be through in explaining my problem.

 

To boil down your situation, you may have a head gasket leaking oil on the passenger side.
The head gasket would have to be replaced. The oil leak is close to the outside edge of the head to block seal where oil is supplied to the valve train under pressure.
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The rest of your issues would suggest you start over again in thinking about the misfire issue.
Due to all that has been done, confusion has brought you here for possible help.
To start with, the dual fuel setup is quite complex.
With misfiring on both fuels at what seems random, my first thoughts are to check the crank sensor plug for good seating.
Next check the fuel trim tables for possible lean condition.
The tables would show rich trying to adjust for the excess air or lack of fuel volume. Look at the gas fuel pressure.
The next misfire possibility is the EGR system. Leaking EGR valve, EVR sticking open a bit allowing vacuum to pass to the EGR and opening it a small amount.
Random misfires often will not set codes and are cancelled if not a hard fault.
What are the misfire monitor telling? Are they high or acceptable.
Which cylinders are the highest etc.
Never 'expect' all cylinders to be zero count at any given time for a number of reasons. Fine if they are but may not be.
I noted your misfire monitors showing 9 cylinders etc. These Scanners get confused at times and need time to gather info from the PCM in serial form so is a bit slow down loading to the Scanner, sometimes. They do V10 motors but you only have 8 cylinders.
If you still have misfires after addressing the above, suspect faulty coils.
Never rely on the thoughts of how old any part is because they can fail out of the box new or at anytime and cause you to run in circles chasing troubles.
Try working from this point and gas operation only first, and see what you come up with.
Good luck.

 

Should I replace the head gasket before I take care of the misfire problem? I have been putting it off until I have time off work and money at the same time. Who knows when that will happen.

So far I have used all motorcraft parts. Should I stick to that if I find any sensors are bad?

What do you mean by good seating for the crank sensor? I assume you mean that it is not loose.

The fuel trims look good to me, both the STFT and LTFT are usually right around 0.8 to 2.3 +/- Sometimes the STFT go up to about 10 +/- when I am decelerating, but they drop back down after a second or two. Both banks are usually very close to each other in the readings.

I have not checked fuel pressure for either fuel. The scanner does not show fuel pressure, so I would have to get the type that attaches to the fuel rail.

During the summer I tried disconnecting the vacuum line from the EGR to see if that helped and it ran worse I believe. (I did plug the vacuum line when I tried this)

What are the misfire monitor telling? Are they high or acceptable.
Which cylinders are the highest etc.
Never 'expect' all cylinders to be zero count at any given time for a number of reasons. Fine if they are but may not be.

The misfire monitor is displayed in hexidecimal. Usually I get a reading of 0051 when I have a misfire. Sometimes it is 02FA or 0755. The 0051 reading is the lowest I believe since any other reading is when the truck feels like I'm riding a bucking bronco on a dirt road. When the truck is running smooth the monitor shows 0000 for all cylinders.

I noted your misfire monitors showing 9 cylinders etc. These Scanners get confused at times and need time to gather info from the PCM in serial form so is a bit slow down loading to the Scanner, sometimes. They do V10 motors but you only have 8 cylinders.

Today I had 6, 7, 8 & 9 cylinders displayed at various times when I was checking. I also have to check it several times before it will show any misfires. In other words the engine is clearly misfiring, but the monitor shows zero count for all cylinders.

If you still have misfires after addressing the above, suspect faulty coils.
Never rely on the thoughts of how old any part is because they can fail out of the box new or at anytime and cause you to run in circles chasing troubles.
Try working from this point and gas operation only first, and see what you come up with.
Good luck.

Today I got the U1262 code again, I believe it maybe contributing to the problem since I had trouble getting the scanner to link up with the PCM. I think the wring at the firewall may be suspect since the communication problem got worse after I checked those plugs.

Thanks for your help, I really don't want this problem to defeat me. The frustration has got me thinking about going old school and getting a 70's or 80's truck with carburetion.

 

I would clear up the misfire issue before the head gasket job.
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The crank sensor is at the front down behind the A/C compressor.
If the crank sensor has any issue nothing else works correctly.
This sensor is the reference for all other functions.
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Fuel Trims are acting good.
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There is no PCM readout for fuel pressure. Only by gauge on the fuel rail.
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Disconnecting EGR hose should not have shown any effect because it normally is not active anytime except in OD at low throttle openings and in third at low throttle openings.
Maybe this is your misfire issue.
Any uncontrolled exhaust feedback will upset drivability.
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The U1262 code is indicating a communications buss issue that could affect the use of a Scanner.
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Misfire monitors do indeed present the count data in Hex.
Use your computer to translate Hex into decimal from the program list under Accessories that brings up a software calculator. Input the Hex # and hit DEC for the translation.
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The Scanner should tell you 'High' if the count is outside acceptable limits.
The mode 6 function can show issues before they set a code.
The monitors will register, moisture caused misfires, boots with pin holes, plug issues, coil issues and cylinder mechanical issues. It just can't tell you which ones are the cause.
It does all this by one simple operation, that of measuring crank rotation time every time the a coil is timed to fire.
What does this time measurement? the Crank sensor.
Hang in there. You have to show the computer you know how he works.
Good luck.

 

OK, so I checked the connection at the crank sensor and it looks fine. Is there a way to test the sensor?
I ordered new motorcraft coils. I replace the coils on #7 and #8. I got the misfire count on #8 to drop from about 762 to 81. I tried another new coil on #8 and no change. So I changed the spark plug on #8 and no change. I tried another new spark plug and changed the gap from .053 to .056 and the count went from 51 to 408. I changed the gap again to .051 and the count stayed the same. I checked the compression on #8 and got 110 psi, I didn't check any others since this didn't show signs of a bad valve or bad rings.
1 So could the coil wiring be suspect?
2 What kind of problem with the EGR could cause this?
3 Could a broken valve spring be the problem?
4 could the injection port the gasoline injector shares with the CNG injector be partially blocked?

Thanks for pointing me towards the hexidecimal convertor that helps a lot.

 

Making a change won't show up in the misfire monitors quickly so you might have gotten misled.
I takes time for an update to occur.
The cylinder's ignition plug gap is not that sensitive to a small change or you would be putting plugs in every 20,000 miles.
If cylinder 8 has compression much lower than the average it will be seen as a misfire because it's rotation time is measured and would be below the average time for all cylinders..
Pull he hose of the EGR and plug it.
If the misfire goes away you found one source. A leaking EVR solenoid.
Good luck.