Got a 99 F-150 XLT 4x4. Triton 5.4L

Codes pulled: PO300 (random Miss), PO306 (Cyl 6 Miss), and PO401 (EGR reading Not suffic)

From a cold start, engine RPM and power seem to be OK, but after engine has warmed up, she starts to sputter and stutter. I do know I need to replace my entire exaust system very soon, but other than that Im unsure. Plugs and boots where changed this time last year.

Any help pointing me in the right direction would be nice. Thanks in advance.

 

i would lean toward plugs/coils or wires wich ever your truck uses. though you already replaced the plugs i would start there with a good quality plug from the local parts store. as for your egr valve start by seeing that it opens correctly bu applying vaccum to the the valve. this is best done with the egr removed, put vac. to egr to see that the egr opens fully when the vac. is applied, then when vac. is removed the valve should complety close. if not you my friend are in need of a new egr valve......good luck

 

Yes, as long as it's a Motorcraft.

All 5.4's use coil on plug.

That is easiest done by disconnecting the vacuum line from it, starting the engine, connecting a length of vacuum hose to the EGR, and sucking on it. The idle should drop and it may stall.

 

so far ive switched No6 coil with another cyl coil. still missin on 6. I'll try a new plug.

If plug doesnt help my situation, what could it be after that? I'm not quite sure where to go after that. Thanks to all.

 

Got it,

I forgot to clear the codes after swaping the coils. Trouble code followed the swap.

 

If you have a rusted open EGR tube at the manifold, 4xx codes will follow.
A seperate issue.