2006 Ford F-150 Multicylinder Misfire code P0300

MIEC

MEMBER
2006 FORD F-150
5.4L
V8
4WD
AUTOMATIC
84,000 MILES

I keep getting the multicylinder misfire code on my vehicle. I have replaced plugs and coil packs, run injector cleaner through the tank, checked for vacuum leaks, intake leaks, cleaned the mass air flow sensor, checked electrical connections on the injectors. All appears to be in good working order. You cannot tell the engine misfires and I do not notice any performance issues. The only reason I know there was a misfire is that approximately every 200-300 miles while I am driving down the road the check engine light comes on. I reset and it repeats. I am wondering what could be the issue or what I could try next. I have read that a blocked or bad catalytic converter could be a cause. Any ideas.

Thanks.

8 Replies

HMAC300

MECHANIC
48,601 POSTS

Check your fuel pressure with a gauge it may be low. Other than that take to a local pro so he can scan it in real time to see if any sensors are messed up. These are hard to find and it can be any sensor messing up causingthe problem. Cheapest way with this code is to take to a pro.

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Friday, October 9th, 2015 AT 9:45 AM

MIEC

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Could you forward my question to another tech please.

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Saturday, October 10th, 2015 AT 5:15 AM

JACOBANDNICKOLAS

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The first thing we need to determine is which cylinders are misfiring. Do you have a real time scanner which can show you where the problems are coming from? The interesting thing is that you don't feel the misfire. Thus, it could be fuel pressure, a bad regulator, even spark plug gap.

Let me know if you have the aforementioned type of scanner. If you do, watch live data which should show specific cylinder misfires while you drive and freeze frame them to review.

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Tuesday, October 13th, 2015 AT 10:57 AM

MIEC

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Thanks for the reply! I don't have the real time scanner only the code scanner. It does give some real time info, but does not tell me which cylinders are misfiring. It is also an intermittent code as it is currently happening every 200-300 miles. I don't have any convenient place on the fuel rail to check to check fuel pressure unfortunately. I could replace the fuel filter, but it actually looks fairly new. Vehicle only has 84,000 miles. The spark plugs and coil packs are new. Plugs are iridium type and you cannot adjust the gap. I cannot find any vacuum leaks. I get the concept of watching real time data, but the chances of experiencing the misfire during the test is low. Any other ideas?

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Tuesday, October 13th, 2015 AT 11:34 AM

JACOBANDNICKOLAS

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First, sorry for the delay. I had a family emergency out of town and just got back.

I totally understand what you are saying as far as identifying which cylinders are causing issues. However, most times, the cylinders will misfire once or twice. Not enough to set the light. So even thought it may seem like it only happens every 2 or 3 hundred miles, it most likely is happening all the time, just unnoticeable.

Okay, this makes things a little tougher because a random misfire could be any of the cylinders. I did some research to see if there was anything listed under a Technical Service Bulletin and found nothing. As far as the fuel pressure, it is possible. Have you checked the fuel pressure regulator? Also, if there is no schrader valve on the rail, the easiest thing to do is to tap into where the fuel filter is located.

Other questions. Do you ever get a strong fuel smell? Has the fuel mileage dropped? Can your scanner tell you real time info on things such as the coolant temp sensor, short and long term fuel trims or anything that might help identify the fuel usage or what the computer thinks is happening?

Thanks,
Joe

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Monday, October 19th, 2015 AT 5:40 PM

JACOBANDNICKOLAS

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After thought.

You asked if the converter can cause this problem. Yes; however, it usually ill set other codes such as a P0420 (converter below efficiency) or codes related to the O2 sensors. Cars used to be quite easy to work on, but now everything is tied together in a giant web.

If you have any concerns related to the catalytic converter, after driving the vehicle for some miles and having the engine completely warmed up, take a look at the converter. If it is plugging, they will usually glow red hot due to restrictions.

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Monday, October 19th, 2015 AT 5:45 PM

MIEC

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Still getting P0300 random misfire code at random intervals. Code is set during high speed interstate driving and appears to come on during loaded or even decelerated conditions. I have replaced spark plugs, coil packs, fuel filter and the main vacuum line. I have checked for vacuum leaks and have not found any. I can read some live data on scanner such as MAF.5 lb/min and O2.68 V. I don't see any red glow in the catalytic converter, but I also do not feel much back pressure (with my hand) on the exhaust system in general. I don't know how to test for what adequate exhaust back pressure should be. I don't believe misfire is related to spark or fuel. I have checked to see if there are pending codes prior to seeing the light and there are none. You cannot feel or notice the misfire and it clearly is not happening all the time as I would expect a pending code to show up as soon as I reset the check engine light. In fact I can drive for days after I rest the light before it comes back on and it only comes on while driving on the highway at higher speeds.

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Saturday, October 31st, 2015 AT 7:33 AM

MIEC

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Also gas mileage is good 17-18 mpg. I don't smell any fuel issues. Also I do have coolant temp and some other live data in the scanner. Everything shows up pretty normal.

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Saturday, October 31st, 2015 AT 7:36 AM