I heard a "thump" on the way to work and 2004 F150 5.4L (103,000 miles)started running extremely rough. I drove it to the shop (5 or 6 miles) and they said it is showing a vacuum leak code and a bad coil on the #1 cylinder, but they can not find a vacuum leak. It is putting out a exhaust smoke (white/grey) but their is no water showing up in the oil.

The mechanic told me my that is has a full vacuum in the crankcase when running. He said he could not remove the oil cap when the engine is running.

Anybody have any ideas?

Thanks

 

take it to a mechanic who knows what hes doing....vacuum in the crank case lmfao

also a vacuum leak will make it run LEAN.

 

A mechanic friend of mine (different state) said basically the same thing. he said it was probably a leaking vacuum line on the back of the intake (he said he has seen this before). He also said you have to take the intake off to get at it.

 

Whats so funny about vacuum in the crank case?

Thats what positive crankcase ventilation is all about.

Larry

 

Maybe that thump was a sparkplug that has blown out on cylinder 1. I would pull the COP and sparkplug on cylinder 1 and inspect it for damage.

Larry.

 

he said full vacuum as in like 18in

most common vacuum leak is the pcv elbow on the back of the intake and no the intake does not need to be removed. i cant really see it being a blown plug or it would have been more then just a thump. you would be sounding like a helicopter. get the misfire sorted out and go from there.

 

I guess I took full vacuum as a relative term as in a 1 oz cup is full and an 8 oz cup is full relative to the cup size.

 

I found out what was causing the full manifold vacuum I was seing in the crank case. Dealership performed a diagnostic test on the engine that measures the resistance of each cylinder in the firing order when the starter turns over the engine. The test identified that the #1 cylinder had 35% relative compression. The Ford tech said the low reading indicated a bad cylinder. He said air is passing around (or through) the #1 piston which is creating the vacuum in the crank case.

I found a low mileage replacement (from a roll-over) and I am planning to pull the old enegine this weekend. I will pull the head and post back if the diagnosis from the dealership was correct.

Has anyone else had this problem? My truck only had 104,000 miles.....so to say I am disappointed in Ford and their engines is an understatement.