Hello,
Looking for any ideas.. Working on 2011 F250 w/6.2L.. Came in missing on 6 cylinders 1-4 ,7 & 8... Spark & Injector pulse good, compression good on all cylinders except 5 (one that is hitting) which is down 20% by scanner and about 30psi checking with guage..Spark plugs were not soaked.. Tried injectors no change.. Vacuum guage fluctuates rapidly.. Codes were misfire related.. Pulling hairs here.. Any suggestions would be greatly appreciated..

 

MOTOR Magazine Article | MOTOR Information Systems

If vacuum is steady at idle but lower than normal, the ignition or valve timing may be retarded. Low compression, an intake leak or tight valves also can cause low vacuum at idle.

If the vacuum reading fluctuates within the normal range-the gauge needle bounces around a lot-uneven compression (broken rings or leaking valves or head gasket in one or two cylinders) is a likely culprit. An uneven air/fuel mix, erratic ignition timing, a misfire, misadjusted valves or a manifold leak near one or two cylinders also are possible causes.

If vacuum drops intermittently at idle, one or more valves may be sticking open or dragging. Higher-than-normal vacuum at idle is a common clue to overly advanced ignition timing, while low vacuum can indicate retarded timing.

Low vacuum also can be an immediate clue to a plugged exhaust. To check further, run the engine at about 2500 rpm for about 15 seconds. If vacuum drops during this period and does not increase when you close the throttle, you're almost certainly looking at a restricted exhaust.

 

If compression lost you have a few different culprits-head gasket leaking, bad valves, or a cam issue. Possibly in the bottom end.

 

Sorry, I did not word the compression part so clearly.. #5 is about 30 psi below the rest.. It has about 120psi where the rest are around 150.. The vacuum guage is fluctuating rapidly at idle...

 

120# is acceptable.

You have checked all coils and wiring to the coils correct?

 

On that engine it is near impossible to get wired incorrectly.. That is not an issue.. From what customer said it dropped 6 cylinders at the same time.. About 30-40 miles after refuel.. Fuel quality does not appear to be an issue either though..

 

Have you tested the pump to make sure it is giving adequate flow?

Are you sure they didn't put diesel in accidentally?

 

I might say one thing , Water in Fuel . I have had 3 trucks towed in, in the last 3 weeks . They all had water in the fuel . I have also had 2 drive in with similar miss fires . The ethenol in the fuel attracts more moisture than the old fuel blends . Just a thought !

 

If number five is the only one without a misfire than it has not had its fuel supply taken away yet either, working harder to cover the dead weight of other cylinders, diluting the rings a bit prolly. I would look at the fuel very close. Sometimes its hard to smell out the diesel/gas depending on the mix if thats what happened. Sometimes you just get a skanky batch of fuel that smells right and looks right but the volatility is off. These newer engines these days don't tolerate questionable fuel like the old days. Emptying the tank and adding known good fuel at the very least will eliminate variables for you at this point going forward.

 

I would also examine the engine closely for vacuum leaks.

 

For sure.....with that many cylinders missing your looking for something that affects all cylinders. Bogus sensor input is a possibility as well.

 

Truck was filled at very busy station.. Fuel volatility has to be fair enough if can run on two cyl's , literally will run on 5 & 6 with all other coils unpluged.. Water in fuel possible and too easy not to check for.. Again though, replaced all injectors with no change.. Do believe have an effective vacuum leak in possible valve problem on 5... Having a problem believeing this is killing 6 cyl's though.. My thinking is corrupt software or bad sensor input also.. Keep in mind same cylinders are being affected consistantly.. Many of thoughts I have had and some of the suggestions should be affecting all cylinders randomly.. Thanks for the imput, will check a few things you all have suggested.. Will be later this evening though..

 

That's why I suggested a possible wiring malfunction

 

Mike, Not following your last post???

 

What ended up being the issue on this truck. My dads truck is doing the exact same thing.