SALT61

Hello, not sure what happened to my intro thread, submitted a while ago but I am going to start my "please help me" thread now in hope of getting some input before the weekend.

Truck is new to me, less than a month. 2001 F150 XLT Extended Cab w/ 5.4L SOHC FI. No apparent engine issues when test driven/purchased. First long drive/highway speed started to run rough after rest stop and Service Engine Soon light flashed but did not stay lit. No codes registered. Went away after second stop. It did the run rough thing on and off on city driving over the last week or so. Yesterday what I am assuming is an engine misfire happened again and this time the Service Engine Soon light stayed lit. When I got home I checked and there was a P0303 Cylinder 3 Misfire Detected code registered. Truck has 152000+ miles. I am thinking maybe plugs and or cops replacement. There was/may still be a vacuum leak. I was having a problem with the HVAC output switching from panel to dash on acceleration but stopped when I replaced the vacuum line from the vacuum reservoir, the one with the check valve. I am just hopping I can get this to work. Any all ideas and input would be appreciated. I do understand that I should use Motorcraft plugs only SP479 is the current for the original ASFW-22. What about replacing the cops (coil on plug). There are many after market, are they OK?

Look forward to talking.

Thanks,

SALT61/Stanley T'''

white89gt

Motorcraft or Denso are the ONLY way to go on these modular motors. Anything else just doesn't last, or doesn't work to begin with.

Check Rock Auto, they are usually the best price on Denso.

mbb

Make sure no coolant/water leaking into spark well

Swap coil from #3 with #1.
Does problem move to #1?

Yes- replace coil with motorcraft or denso....ONLY
No.....swap plug /injector with another good cyl.

If problem moves, replace bad part
If it dont....time to look at #3 compression, etc

SALT61

Thanks, makes sense to see if it is isolated. I assume I should not drive until I have figured the problem out?

mbb

When engine light flashes....it means misfire is high enough to damage cats with unburnt fuel....melt them basically.
Expensive enough.
But if that do happen, it can cook that side of engine, melt pistons, stuff like that

So yeah, avoid driving with flashing light

SALT61

I assume "cats" is catalytic converter? The Service Engine Soon Light is constant. It only flashed once for about 10 seconds at highway speed several days ago but did not stay on at that time and did not light again until yesterday morning and that was no flashing just light on, stay on. I sure hope I did not ruin the whole right side of the engine by not stopping on the highway. I guess we will see. I am going to swap out the plug and the coil from 3 to 1 and see what I get. One thing I wonder though is how would go about getting it to throw the error without running/driving? Should I just start, let idle and then stop and repeat? I think I recall that a code must be encountered 3 times to register. I that correct? If so then just start and stop 3 times? I do appreciate the feed back very much, glad I joined/came here. Thanks again.

white89gt

Yes, cats is catalytic converters. Mine flashed about 10-15 times when it first threw a misfire code, then went solid. No engine or cat damage was done. I only drove it another 15 miles after that though.

mbb

I drove 20 with it flashing one night, no damage.
Just saying, its not a good thing, and could be bad.


Your gonna have to drive it to throw code. Most likely. Mode 06 data will show it first.

R&TBabich

If problem doesn't move I would also check for 12v to the COP and injector connectors.
Then test for 12v thru the COP and injector to the PCM connector input pins.

SALT61

Thank you for all the ideas. Looks like I'm going to have a busy Saturday. Just to make myself feel a little better I went to the salvage yard today and found the 5.4L throttle body cover and a replacement out side passenger door handle and I took the tumblers out of the old lock and put it into the new one so now the passenger door key lock works. YAY me! I will let you guys know what happens over the next several days. Thanks again