2000 DOHC Taurus P0306 Miss on cyl 6 at idle

Hi guys,
Hope some has an idea what this could be. I'm getting a P0306 Cylinder 6 Misfire Detected. So far I have switched the coil pack and plug with cylinder 5, no luck same code. So then I switched the fuel injector with cylinder 4, no luck same code. <---What a a pain that was!!! Checked compression, it was at 150psi and 5 was at 180, don't think that would be enough to cause the problem. That's higher than my mustang on a good day lol. Problem is that it only misses at idle like when I'm sitting at a long stop light. Anyone have this problem? Need help!!

Thanks,
John

Generally the rule of thumb is 15% variance between cylinders is the max allowable in pressures, possible you have a burnt valve or a lot of carbon that's keeping it from sealing, what happens to the pressure reading when you put some oil down the spark plug hole?

Not sure didn't try that. I'll do a leakdown test this weekend to see if there is a bad valve or ring. I'll post what happens.

Well I did the leakdown and the cause of my problem is definately in one of the exhaust valves. I could only hold 70psi of air in that cyl and had a steady flow coming out the tailpipe. Checked cyl 5 to compare and it held 110psi (that's the line pressure I'm working with) no problem . Grrrr... I'm going to put some Seaform in it just to be sure that carbon isn't holding it open. But I seriously don't think thats it.

I have changed cylinder heads on a pushrod motor but never on a DOHC moter. Is there room to do it in the car? Sure don't look like it@! If someone has done this before please let me know what is the best way to go about it.

Thanks,
John

Check the valve springs on that cylinder before condemming a whole head job. Springs breaking are pretty common, unfortunately I've never done too much engine work on that engine but a good Chilton's manual should be able to walk you through it or if you don't have the tools time etc, maybe cut your losses and call a professional. Ithink you can change the springs without removing the head if you keep air in the cylinder

I was thinking the same thing, I should be able to see it the valve is completely closed with the valve cover off. Believe me I don't want to change that head, doesn't look fun. Think it might be easier to take it to my father inlaws, he has a hoist, and raise the car up off the engine and trany. Doesnt look like the drive train is held in by much...lol ya right..
But on the other hand if the sping was broke I would be getting valve float and at high RPM, and this car runs great except at idle (sometimes). I'm still going to check that spring, you never know, it would be sweet if that was the problem!!

Thanks for the advise,
John

valve won't necessarily float, broken spring will keep valve from coming up all the way, if valve is open it'll either carbon up and or burn, Probably that cylinder misses all the time but without scanner too watch it all a speeds and loads you won't see it.

I have the same problem on my 2000 taurus. What did you find out was wrong with your engine?

Thanks

I replaced the motor because of the miles on it. Purchased one from the boneyard for $600 with around 45000 on it. It took an entire weekend but really wasn't to bad to replace. Didn't open the old one up beside taking the valve cover off, springs were fine. That cylinder was always down on compression even when it wasn't missing. Had to be a valve guide or maybe the valve was tagged by the piston and slightly bent or burnt.
Runs like a champ with the new motor, we have over 100k on this motor now.