'03 5.4L runs great but occasionally when I am accelerating, I feel the engine miss and at that same moment I notice the Theft light blink. It is not the coil packs or the plugs. This has been doing this for a couple months now and seems worse with a full tank of gas (if that makes any sense...)

It's like the anti theft system is cutting out the ignition very briefly.

Any ideas?

By the way, there are no tripped codes or even any 'preliminary' codes as scanned by a Snap-on scanner.

 

Does it do it with your other key?

 

It is impossible for the PATS system to do this. After the engine has been running for a second or so, PATS has no further effect on the operation of the engine and CANNOT cause the engine to stop running.

More likely, you are experiencing an intermittent loss of power to the PCM. I'd start with a new PCM Power Relay.

 

Thanks for the replies.

I'll try the other key for what it's worth but the power relay idea sounds more likely. Just have to figure out where it is now... Searching now.
As for the full fuel tank, I suppose the heavier weight puts more load on the engine which makes the problem more noticeable.

I have read about radio capacitors causing related problems. I'm wondering if my capacitors are starting to short...when listening to AM radio I hear a huge whine associated with engine RPM. Does that make sense? Confirm the PCM fuse (relay) is located in the passenger compartment??

 

See owner's manual for relay location.

If the RFI capacitors on the COP supply circuit were to short, a fuse would blow and the engine would stop running. Yours might be open or disconnected. Also common is for the base of the antenna mount to corrode and loose its effective ground connection to the fender, allowing RFI to enter the AM receiver. I'd start there for the AM static.

 

Relay is on order and will be in tomorrow. By the way, I see the red factory alarm light on the center of the dash blinking sometimes too which I think is related to this relay.

Anyway, I can't find the Capacitors and believe they should be mounted to the brass threaded mount in the dead center of these pictures. Is this right?
If I did get capacitors, I don't see any connector for them to hook up to. I have the Haynes manual and it makes no reference to capacitors at all.

Left side of engine. (front towards bottom)



Right side of engine (front towards bottom)

 

OK I put in the new relay and it didn't make any difference. Still no codes either.

What about the capacitor location; or lack there of?

 

so no codes?

and how do you know the COPS and plugs aren't in need of replacing?

 

I have replaced them a year ago. The misfire then was accompanied by codes. Now I just have a fairly minor misfire that isn't bad enough to trip a code and hasn't got any worse in two months.

 

What brand plugs and cops did you use?

 

The COPs were some Chinese ones off of Ebay that people here had said were alright and I can't find the bill for the sparkplugs but I really doubt I would have used anything other than motorsport ones. (I previously had a Supercoupe and learned the sparkplug lesson the hard way there.)

 

sounds like you learned your COP lesson the hard way as well

 

I always thought that Chinese=$H!te but those COPs were the ones people on here were raving about. What's the recommended brand now? Ford at $70 each or are there any available on Ebay that actually work?

Any thoughts on my capacitor situation? Shouldn't they be visible in those pics?

 

Does anybody have capacitors on their 5.4L engines? If so, can you please verify where they are.
Thanks.

 

Most here (including myself) recommend Global cops from ebay...