Hi yall,
My boss has a '00 F-150 running a 4.6. She's got about 125,000 miles on her clock and is an absolute bear to drive. Today I hooked up a vac gauge and started her up. In park the needle holds in the green, albeit on the lower end, but still in the green. When I put it in gear the needle drops down into the late ignition timing region. If I start driving her around the needle drops down further into the late valve timing region. As a result Gas is flooding into the oiling system

The computer is spitting out cylinder misfires along with 1151 (lean O2 Sensor). I replaced both O2 Sensors today but to no avail.


The plugs are all new, I've tested every COP at least twice, those are all normal. I've tried listening for vac leaks but I don't really know what I should be listening for specifically.

He keeps saying that it seems to run worse in humid weather but to me the truck doesn't ever seem to run well. Maybe this comment will help you guys.

Around 1400 RPM the vehicle shudders like a cheap motel bed. Higher octane gasoline (93) used to be able to stop all the hesitation, stumbling, & lack of power but now, does nothing.

If anyone can give me some advice as to where I should go next please let me know, I'd be very greatful.

Thanks folks
Chuck

 

Check the exhaust system. See if it's plugged. Easiest way is drop it loose from the manifolds for a short time and see how it runs.

 

I think I'd also try cleaning the MAF sensor and check closer for vacuum leaks. Rather than just listening for a leak I like to spray Carb-Medic spray carb cleaner at the places I think there might be a leak. If there is a leak the idle will change as soon as the Carb-Medic hits it. A good place to look for a leak is the PCV hose.
You could possibly have a stuck open EGR valve as well but that should set a code.

 

"gas is flooding into the oiling system"

Do you have gas in the oil? Shudder sounds like a misfire, worse in humid weather...sounds like water on top of a plug...COP boots dry? Check the boots and plugs on the coded cylinders for liquid, P1151, as Racerguy said, look for collapsed PCV hoses (on each end of plastic tube).

 

I'd place my bet on either a vacuum leak at the PCV line or a bad lower intake manifold gasket. I'd check the PCV line for cracks. Part of it is rubber and part of it is plastic. Look for splits in the hoses, particularly at pre-molded bends and plastic/rubber junctions.

In the shop, we have a smoke machine to look for leaks. You will only hear a leak if it is really massive or through a really small line.

Does it have a plastic intake manifold? Those used to have gasket failures. If you restrict airflow to the throttle, the motor will rev up if you've got bad gaskets. Also, look for cracks in the intake hose anywhere between the filter and the throttle. The MAF is located in the Air Filter Housing (Side closest to the motor). That's the other thing...choke flow on the other side of the MAF if you can.

I have another not previously seen item to offer as a check, but I would kinda expect it to set a rich code rather than a lean code. Is the fuel pressure regulator OK? I'd also check the fuel pressure and make sure the regularot isn't leaking gasoline into the vacuum line. I'm a fan of shots in the dark from time to time, and I've seen this happen before.

BTW, does your scanner break down the Lean/Rich condition by Engine Bank? If it's just one bank but not the other, I'd be more inclined to point toward a lower intake mfd. gasket.

 

Multiple misfires? New plugs were installed? What kind? Triton's are a bit finicky about plugs.

 

Thanks for the help so far guys.

Bank #2 is shot back as leaning out.

The plugs are all Autolite Platinums. I'll run through this list tomorrow and see if I can score a hit. I've got the day off today so I'm gettin my grand wagoneer back into shape.