I have been getting a code 306 for sometime now, ignoring it as the engine didnt seem to be missing, however, I finally got in there to get a look and found the spark plug was loose in the cylinder. Well, I tightened it back and connected everything back. While under the hood, I could hear a vacuum leak. Looked, sprayed what I could see with WD-40, never could pinpoint the leak. Throughout the day today, it ran rougher and rougher. I replaced a couple of suspect vacuum lines, appearing to be rotten, but not showing leaking with the WD. After I changed the lines, it idles just a little rough, not bad, but enough to notice. But boy, when I put it in gear, look out. It gets real rough, and I think I can still hear a vacuum leak in there, no check engine light ( which makes me more sure that I have a leak), but I dont know?
Can someone enlighten me on this, am I thinking the correct thing here? Thanks in advance.

 

What truck/ what motor? Fill in the information in your profile so we can help you,

 

When was the last time you changed the fuel filter?

If its a COP, change all of them, and get new plugs.

 

There is an elbow that is notorious for leaking. Check out the picture in this post #45 from jbrew...

https://www.f150online.com/forums/sh...k+elbow&page=3

Another possibility is that the diaphram inside the EGR valve has a hole in it.

 

I changed all of the vacuum lines that I could see, even what I think is the notorious one, checked compression, 150 lbs each cylinder. If I unplug the 4 and 5 cylinder wires off of the coil pack, the engine doesnt respond, which is why i went wires and pack. It still idles rough and all but dies out when put in gear. I don't know what other vacuum lines I'm missing. Anyone else got input?

 

So you disconnected the packs to cylinder 4 and 5 and the engine did not seem to run rougher?

You then replaced the coil packs on cylinder 4 and 5 and disconnected each pack and the engine still did not run rougher?

How many miles are on the vehicle and when were the spark plugs last changed?

 

144,000 miles, I just replaced the plugs, wires and coil pack. Engine still running rough. I plan on checking fuel pressure this afternoon. I am pretty sure I have replaced all the big vacuum lines, and I also think that I still have a leak, but not sure where. I pulled off teh vacuum off the brake booster and I have a very strong vacuum there, also checked vacuum at pcv, it feels strong there too. Not sure.

 

What a treat a memory is....I was talking to a friend about this and AHA! I remembered that before I put gas the last time before this problem, I ran it past E, damn near sucking fumes. Replaced the fuel filter (very brown gas coming out of it), checked fuel pressure, 30lbs just like the book. Still missing worse than ever. I also put my spark plug tester inline at the plug, I have steady fire there. So, just for the heck of it, I pulled off the plugs to see if 4 and 5 were still not firing. Again, with 4 and 5 wires off the coil pack,(at the same time) doesnt affect the engine at all. What I'm thinking is cause I ran my tank so low, I more than likely picked up some trash from the bottom of my gas tank. I'm going to pull the rail off and clean all of it out, and hopefully, I find some trash n the rail or stopping up thest 2 injectors. I think I'm getting close. Thanks.

 

That explains it - 30 lbs pressure ? That's a bad pump, replace that and you'll prolly be set. Unless you used Autolite or Bosch plugs - Then your screwed until you use the right replacments for that 99. = Motorcraft ONLY!! If you want it to run right. Some will run for short time with the wrong plugs, but not good. Some - Like my 98, wouldn't start w/Bosch Plugs and ran on 8 cylinders for only 40miles w/Autolites.

BTW - That's good compression - 150 - same on all 8 AND - These pumps are all bottom feeders , they suck from the very bottom of the tank 100% of the time.

That should give you some idea .. ?

 

I used OEM plugs, I don't like to drift too far from OEM when replacing parts. The Haynes book says 30-45 lbs of pressure for my 4.2, I know Im on the low end, but you think it could still be the pump? Just not enough for the 4 and 5 injectors to have? I don't know, u know 100 times more than me, believe me. But, here's a little something I woke up with also. The schrader on the fuel rail is between cylinders 5 and 6. My problem seems to be somewhere before that. Injectors for this truck are around $50. So, knowing what I know about the fire going to those 2 cylinders, shouldn't I be going straight to those 2 injectors? I would have no problems changing a pump, trust me, I am just not getting why you are thinking pump (I need most things drawn out like a picture), could you please run that by me again? I am trying to type all this out and not seem like a wisea$$, believe me. If I knew it all I wouldn't need to be in here in the first place, I appreciate your help, just not understanding the logic here. Thanks.

 

Here's the latest... I'm going after the fuel pump, cause my pressure is at the low end of the scale, and knowing what I know about fuel injection, can't be a good thing even if I were to lose just 1 pound of pressure its all jacked up. Then I'm going to change both 4 and 5 injectors

 

Now I'm lost. I replaced the fuel pump, both suspect injectors, fuel pressure is 32-34. I still have the same original problem, I don't know what else to try! Does anyone have any suggestions? Thanks

 

I found it. . I had two wires (banks 5 and 6) swapped on the coil pack. Sometimes the easy things are the hardest to find. Just something to keep in mind , the cylinders are 123 on pass side front to back, 456 on drivers side front to back. Well. the coil pack is 123 pass side front to back, continuing clockwise around the back of the pack 465. I had them exactly clockwise. Thanks for your help . Appreciate it. Jamie.