so im a newer member of these forums, this & one other one . deep roots in ford with my family, my dad still has his 1st car...68 mustang coupe...68-1/2 actually. LOL. doesn't run & she's far from mint but she's all there together with all her badges & still able to make anyone feel time warped when u touch her. LBVS. anyways I LOVE FORD!!!! that s still being subtle...lol So, i got 206 f150 5.4 4x4 as yal may already know from previous trouble shooting on here. truck had rough idle when it her almost a year ago but passed inspection 100% at 173,xxx for $2,400 was giving it to my boy who's 16 this month so I've done a full run through & tune up but now seemingly more than before. I can distinctly hear a hiss from moment it starts through entire running until I shut it down, seems to come from drivers side engine area or fender well. its steady & constant. I've already installed or serviced: new air intake manifold gaskets, new IWEs, New 4x4 hose assembly, new abs sensors, new fuse box with new relays, new throttle body, new O2 sensors, new thermostat, new coolant crossover & gaskets, new vacuum solenoid, new platinum motocraft plugs & edelbrock coils, new starter, new alternator, new battery & cables, new fuel filter motocraft, new intake runner control arm module, new fuel pressure temp sensor, new air filter, new oil filter & oil change Motocraft, differential inspection front & rear, transfercase drain & fill new, coolant drain & flush, transmission drain & flush new filter & fluid, new erg hoses & connectors....still has hiss like a vacuum leak & grinding at front end like the issue with the bad iwes & a moaning or rubbing sound from rear end & idles rough like missing engine light on but i obd2 it daily from my scanner & i clear ir all out it but its reading too lean bank 1 & 2, cyl. 3 misfire so what did i miss or what am i not seeing?

 

check the vacuum box for the hiss, the vacuum box is located by the battery. #3 misfire could be several things, what's the actual DTC ?

 

welcome to

 

my vacuum box is good & its on passenger side behind battery lol mine only has the one battery. could it be the exhaust leak? Exhaust manifold maybe? P0171-too lean B1, P0174-too lean B2 & P0303-Cyl. 3 misfire, all Generic, not pending or current on OBD2 scanner im plugging into laptop now to try for a more detsiled print out

 

swap the plug on # 3 with #2 and see if the code follows, if that don't work try the COP and then the injector. Lean means you have an air leak/vacuum hose. check the foam gasket around the air cleaner box, that get rotted and fall a part. Check the seal on your gas cap.

 

Check the vacuum behind the intake manifold. Check both the line going to the fuel rail pressure sensor and to the 4x4 solenoid plus the big vacuum line going to the evap canister purge valve. And make sure your gasket is seated correctly under your intake manifold. Those sometimes shift last minute and if it's not seated correctly will definitely cause serious issues. Also, if you don't have one go and purchase a smoke machine on Amazon less than 100$ and smoke the top of the engine and that will help you know for sure where your leak is at. I normally use the vacuum line going to the brake booster to plug into when I use a smoke machine. If you suspect a leak on the exhaust manifold you can also use the smoke machine by plugging it in at one of the o2 sensor locations. Preferably the downstream because it's easier to get to and remember to tape off the end of the exhaust pipes when checking the exhaust. Clear packing tape works great. But I bet you will find a b leak on the intake manifold gasket or the vacuum lines coming from the back of the intake manifold. That's the most common locations for this engine. Your cylinder 3 misfire might be caused by poorly seated spark plug or check the spring inside the coil pack. Make sure it's making good contact and of course the plastic plug connectors get brittle and if they don't snap when connecting them replace it. You can get a set of 8 off Amazon for 12$.. as well as fuel injector plugs same price. I learned after troubleshooting over and over that splicing a new connector onto the wire harness and giving the engine fresh wire connectors makes a world of difference. The wire that's plugged into the back of the connectors get bent and look like a crooked mess. If they look like that most of the time the wire is broken inside the casing and it might look like no problem but actually it's not making a good connection and causes misfires over and over.