Have any of you ever received this CEL code? If so where did you start to correct the problem?

After doing some reading on this code it could be 1 of 20 things.

Funny thing is! Ours only comes up after adding a fuel additive.

We changed plugs 10k miles ago.
Fuel filter 7K miles ago.

I'm fixing to replace all 8 coils.
I have read where a bad battery can cause this code also.

Then my last resort will be vaccum leaks...

One more thing. When the A/C is not on the idle is very smooth. When the A/C is on the 5.4L 3V has a slight vibration at idle.

Curious if any of you have advice on this P0300 code.

 

That's a random misfire code.

Do you have the old style boots (black) or new style boots (brown)? What brand plugs did you use? Did you replace the boots? Did you maybe overgrease them? Did you maybe use too much or the wrong type antiseize on the plugs? How many miles on the truck? What fuel additive are you using?

 

After reading this article I have a better understanding of the RANDOM misfire Code.

Since we just changed the fuel filter. I'm going to start with a new battery since this one is 5yrs old and then have the fuel pressure checked. With 180K miles if figure the fuel pump might be close to retirement. Then I will clean the Mass Flow Air sensor again.

If I read this right. The first place to start looking is a subject that effects all cylinders at once.

http://www.agcoauto.com/content/news/p2_articleid/283

Since the code had been cleared 2 days ago. We put 15 gallons fresh fuel in and drove on the highway 25 miles and in town some and the CEL has not returned. But I still will get everything checked out since my son will be driving this auto back and forth to college.

 

The fuel pressure can only be checked with a reader in the OBD2 port, there's no test port on the fuel rail like the older trucks. If you suspect fuel pressure issues, take a good look at the FPDM for corrosion.

Would be nice if you answer my other questions.

 

GLC: Sorry for not answering them. I was kind of excited about the article that explained more about this issue.

I had my mechanic of 21yrs change the plugs->I didn't have the time nor the patients at the time. He has change hundreds of theses.

Old Style Heads according to the build date of the 5.4L 3V-->Black Boots

Motorcraft SP515 plugs he knows thats the best plug for this application.

He told me the boots looked ok but he replaced with SPB150 boots. Here are the ones he replaced with!

http://www.oreillyauto.com/site/c/de...3758&ppt=C0334

I don't know if he over greased them? We never had a CEL for the first yr after the change, until I had the itch to add a fuel additive.

He did tell me he did apply antiseize-->Only on the smooth part of the new plugs not the threads. He also told me he knows me and I will have this truck for yrs to come and he wants this set to come out just as easy as this set. He has replaced hundreds of sets of these plugs so I think he knows the correct type. I hope!

I had these plugs changed 1 month after we brought it home-->170K miles-->{3/4 of these miles were highway miles} Back and Forth to Houston-->Sales mans pickup.

The truck now has 181K on it as of yesterday.

I really only use 3 brands
Redline SI-1------>Caused CEL
Techron Complete--->Caused CEL
Gumout Regane HM-->Caused CEL

Fuel Power from Lube Control is the only one that did not throw the CEL.

I am fixing to change out all the Coils and Boots before he leaves for college in August. Replacements are Visteon DG511.

I'm think I'm going to rule out a Vacuum Leak. He has put over 200 miles on the truck since I had the CEL cleared-->{Highway Miles} No CEL! I'm being honest here guys!

The Motor Never Throws this code until I add a Fuel Additive. LoL! I am not going to add anything to the fuel all summer.

I'm going to replace the Battery and Coils w/boots-->For reliability issues and Change Air Filter and Oil for the Summer and that's it. No more Fuel Additive!

I was thinking the O2 sensor might be getting very tired and the additive is leaving some what of a residue and it can't process the info properly and there for throw the code?

Any thoughts and advice is more then welcome. I will take the truck to O'reillys to see if they can read the fuel pressure with their machine. Anyone know what the correct Fuel PSI should be?

 

Well today-->I started replacing Coils & Boots. Replaced all drivers side--> Very Easy! All boots looked normal.

Started on passenger side--> #1-#2 -->Boots looked ok.

#3--looked like the bottom of the boot was dark-->like it was burned and had some oil on the bottom of the boot. -->Might have found my misfire-->P0300

I am curious if the mechanic just didn't get the SP515 snugged down all the way?
I will check this tomorrow.

Does anyone know what socket size the SP515 takes? I think I read where it is a 9/16?

#4 is really tough! Will tackle that rascal later!

 

yes 9/16, much bigger than the normal 3/8 spark plugs

28 ft lbs IIRC

 

Thank You--> Patman!