Hi All, bought a cheap used 2005 F150 with some problems. I've been told it has an exhaust manifold leak, and before I cleared the codes I had a code for a faulty ignition coil, which looks to have been caused by a poor connector to the coil. I've got it seated now so I don't think it's a problem. I also have a code for a poor injector on cylinder 3. I removed injectors on cylinders 3 and 2 and cleaned the best I could and swapped them.
I'm not getting any codes now, which in some sense is nice, but it still has a very rough idle, and it doesn't seem to go away over time, driving around and stopping at lights it still has a rough idle.

I bought an OBD2 to usb scanner and forscan, but I'm not sure what to look for. It's not showing any misfires, which is odd because it's shaking quite a bit. I could start replacing stuff like ignition coils and spark plugs and injectors, but I don't want to waste money "guessing" on a fix if that makes sense. I tried spraying WD-40 near the back of the engine to see if there's a vacuum leak, but I didn't see anything suspicious.

Any ideas for troubleshooting further? I've attached a video of the truck at idle.

 

How long has it been since you cleared the codes? It can take a while for the truck to go through a full drive cycle and re-populate any codes.

What's the mileage? It may be time/passed time for plugs anyway for this generation. Lots of folks avoided doing them because of the 5.4L spark plug problem this gen had.

Re: not wanting to spend more money guessing, smart. If you're at this point in your thought process, it's time to start thinking about taking it to an actual Ford service center and paying for a diagnostic rather than doing more guessing. It could end up being cheaper than throwing parts at it when all the cheap stuff is done.

 

I would definitely start with a fresh set of motorcraft SP 546 plugs and some new boots and springs, clean the maf and throttle body change fuel filter and check the air box for leaks and a clean filter.

 

• Did they say where the leak is? If it's at the exhaust manifold, it could be causing the O2 sensors to send incorrect signals to the PCM

• See below

• 100% agree.

• Focus on finding whether there is an exhaust manifold leak. If so, repair it first. JB Weld may be useful.
• Use Forscan to check fuel trim and O2 live data parameter id's (PIDs). This could help diagnose whether there is a problem with the fuel mixture. Also check the PIDs for MAP voltage, engine temperature sensor, closed or open loop, and RPMs.

We can help further with the additional information.

 

First you want to see mode six ,it tells you by cly how many raw computer counts it is seeing towards setting a code,which is quite high . Next see youtube and build a diy smoke machine , it is far away the best to see vacuum leaks . Also you can have leaking injectors that cause misfiresand can ndestroy engine . Lay them out on rail put them on dry newspaper , turn key on none should leak . Hint ---at 270 k i am on my third set of new injectors. Of course you should start with all new plugs /boots .

 

Thanks for input all, sounds like I have a lot of work to do. Will update or make a new thread after I've done more testing.

 

update this thread please.

 

While you're at it, check all the vacuum lines that have the quick connect fittings that snap on. Make sure they are actually clipped on tight. Vacuum leaks will make it idle rough and it's one of the things that's easy to miss or not get 100% right when reassemble after doing some work.

 

Brief update: I managed to change the spark plugs - damn that was some effort, thank god for youtube guides. The spark plugs definitely looked pretty rough - some of them had some soot on them, I guess indicating running rich. I managed to start and after some initial smoke coming out it seemed pretty steady. There was some rough idle, but I haven't had the chance to actually take it for a spin, and also it might be partially in my head - I've never owned an f150 prior to this so I'm not sure exactly how smooth I should be expecting it to be, but it's definitely better than it was.

I just took out the throttle body to clean it, but honestly it already looks fairly clean, see pictures below. I'm wondering if I should be replacing the fuel injectors, or if maybe I have a leaky fuel injector? Oh and I checked the engine air filter and it looks to be pretty much brand new. I might try a new fuel filter too since that doesn't seem to be super expensive, will have to see how difficult it is.

I might just try driving it around a little bit, like I said it's running a lot better than before. Happy to hear any ideas though, I really appreciate everyone's input.

 

Hey again, managed to change the spark plugs, very difficult and thank god for youtube guides. Some of them looked to be in pretty bad shape, with a lot of soot, guess running rich. I managed to start it, and it was running *less* rough than before, but not sure if it's still got issues or not, I'm not exactly sure how normal 5.4l f150's run, how smooth etc. I might end up driving around a bit just to see how it feels (I only started it and let it run idle).

I checked the resistance on the coils, all seem very consistent (1 ohm across connectors, 5.7kohm from boot to connector).

I also checked the air filter as suggested, looks to be brand new, very clean. I took out the throttle body to clean it, but it already looks very clean, pics attached. I may look into the fuel injectors next, since I can't think of anything else that would cause it to run rich, looking at buying the SKP injectors since the Motorcraft ones are more than twice as much.

I may also look into the fuel filter, since it doesn't seem too difficult to change out, or costly.

Any other input greatly appreciated, thanks all!