2004 f150 5.4

When I start the truck it runs fine for roughly ten seconds then it shuts off power to two of my injectors. Or so I thought. With a noid light on, I was getting shutdown on cylinders 1 and 6 as per the codes ten seconds after starting. I assumed this was as intended to stop raw fuel from entering the cats.

So far this is my findings.
Noid light-shuts off the two cylinders after ten seconds. But will pulse again later before shutting them down again. Truck idles better, but never seems quite perfect. Could just be how 5.4's are though.

Swapping injectors did not change codes.

Coil packs are working on those cylinders. Spark test checked out and plugs are firing. They were replaced at some point with oem motorcraft plugs.

ohm test showed wiring to those cylinders was fine. Wiggle test showed the same.

The truck revs and sounds great before it shuts off power to the cylinders. I cannot assume a mechanical failure at this point. I have not ran a compression test on it yet as, in their great wisdom, Ford determined they had to be different than the rest of the planet with spark plug sizing. Adapter will be here tomorrow for me to verify that part. I have checked around quite a bit so I apologize if this has been somewhere else on the site and I missed it. I have exhausted everything minus a compression test. I can only point a finger at the computer currently. But I am not quite sure how to verify that is the issue. And quite frankly, I have never seen a computer go bad without outside help.

On a sidnote, the truck starts very hard at times. Like a car that has heavily advanced timing. It could actually just be a starter issue though. I figured I would get to that after I find out what the other issue is.

 

@Fred Robertson
I trust, from your post, that you know what you are doing but I would like to know more about just how you have determined that the PCM is 'shuts off' cylinders 1 & 6 - reporting the condition as misfires.
The injectors (like the COPs) are sourced +12v with the PCM pulling the negative side to ground through an transistor switch in the PCM. That 'switch' can certainly fail and they are susceptible to failing after the current (& voltage drop) across them heats them up. [but two separate ones - like almost simultaneously?] Have you checked for 'current' in the circuits or presence/absence of a 'square wave' at the PCM end of the circuits? Do you have an engine performance wiring diagram or diagram of PCM connector pin-outs? If not, I have one and can provide a copy.
Also, your post sounds like you have a code reader / or scanner. I would be curious what fuel trims and O2 sensor graphs look like, and freeze frame data. If the PCM is shutting down injectors - it would without a doubt effect O2 readings and fuel trims.

 

I determined shutdown of the cylinders only by using the noid light. I figured it was the computer shutting them down based on the fact that it was the same timeframe each time. Start the truck and it fires on all cylinders(so it seems)for ten seconds then would shut down those two. I do not believe they are simultaneous due to the engine changing notes randomly. IE developing more or less shudder. Sometimes it is none, or one, or both that are off at a given time. I will go recheck the truck with a live data feed to tell you what I see as far as oxygen sensor readings since I do not recall them off the top of my head.
I do not have a diagram of the harness pinout. As far as the square wave, in all honesty you have lost me there. The reason I am concerned about the computer is solely based on what diagnostics have checked out. No harness issue to the injectors at fault, no coil or plug issues, and wiring testing fine. I am somewhat at a loss as to what else could cause such a condition.

I just noticed I had not mentioned yet that the issue is severe enough that the truck will go into limp mode at any type of heavy throttle application also.

Fuel trim is at basically 0 on bank 1 -11 percent bank 2.

 

A completely reasonable deduction. And I have no knowledge otherwise.


Before deciding, I would be curious if the PCM will shut down an injector on an otherwise WORKING circuit plugged into only the noid light. Understanding or reverse engineering of a program requires thinking like the original programmer. Certainly, the cylinder is not firing with the noid lite plugged in, and the PCM knows it in the same way it normally detects misfires (absence of pulse from Knock Sensor and absence of a momentary spike in frequency from Crank sensor ring). The PCM WILL certainly shut down the injectors on a dead cylinder - to save the cat as you suggested in the OP. This however is usually accompanied with a flashing CEL (which you haven't mentioned), although you did mention it going into LIMP MODE. That consists of shutting down cylinders in an alternating pattern, - but not just a couple.


My earlier suggestion of an output transistor overheating is not likely because: The noid light (if that's how you witness the cessation of pulses), draws so much less current than the injector coil - it would never overheat an output switching transistor.


However - I believe I would prefer to do this test by piercing the injector wire with a needle and use alligator clips and an analogue (NOT digital) multimeter. That way you could tell if there's a loose connection in the + side (because it should NEVER dip below +12v at all), and the switch side of the injector should read good solid +12v with ignition on, and bobble downward with pulses at the rate the noid light was flashing with engine running. If the switch side goes to +12v & stays there - either the PCM has shut the injector down, or its output circuit has failed, or an bad connection between injector & PCM (at which point I would move this test to the PCM plug pin for this circuit to verify that). If the switch side sags to or near to ground with only slight bouncing, the internal coil of the injector is going "OPEN CIRCUIT" when it heats up.

I have temporarily placed a wiring diagram on my server here: http://www.devoll.com/public/f150-5_...nce-wiring.pdf and a diagnostics reference chart from the Ford Factory Service Manual showing many pinouts on the PCM Plugs that is often very helpful here: http://www.devoll.com/public/5-4L_3v...nce_values.pdf You should be able to download them and print them out or save them to your computer.


Fuel trims were not helpful just yet. I am curious when the last spark plug change was and how cleanly it was done. It occurs to me the source of this could originate with a damaged plug shorting over inside as the combustion chamber heats up. I have some rather strong opinions about plug changes on these engines, written about here: https://www.ford-trucks.com/forums/1...l#post15059177 and a lengthy discussion about it here: 5.4 issues - misfire - F150online Forums


Maybe this will give you some other ideas or avenues.


Keep us posted.

 

Since you verifed that the pcm will infact shut down the injector due to a misfire, I think I may have gone about this wrong. When I originally saw the injectors shutting off, I ran all diagnostics on injectors and injector wiring. I will have to verify tomorrow that the coil wiring is ohming correctly and also not grounding. I know the coils were firing each time I pulled the wires and checked for spark but that does not mean it was not grounding momentarily at another point. I really appreciate the diagram. I have not found one elsewhere. I only pulled a single plug out of the engine since I knew these have a tendency to break. I will pull both of those tomorrow and verify those cylinders for sure are fine on that end also. Thank you for the ideas.

 

Ok so this only caused more confusion. I bypassed the harness altogether on cylinder 1. Hooked the hot lead up to battery and the coil lead directly to its corresponding wire a few inches from the computer. Still shutting off the injector. Pulled the plug out of the cylinder. Looks perfect. It IS firing as I started the truck with it in the coil and verified this. There is absolutely no reason whatsoever for a code about a coil circuit unless it is inside the computer itself failing.

Bypassed injector directly also. Same thing...

 

Damn! That's not good. I assume by now the PCM connector has been unplugged and plugged enough times to eliminate the possibility of a bad or high resistance connection. Though somewhat unusual - the computers do fail. And though somewhat unusual it can occur on two circuits simultaneously. If we could know the internal circuitry / traces, there could be a common element somewhere.


I couldn't ask for more thorough diagnostic effort - even if you were working on my own vehicle. But it sounds like it's time to suspect the PCM. I have NO experience with changing them out, so you are now above my pay grade. But have seen info here suggesting it is not too expensive, and not too much trouble provided it is the same make / model and or code numbers somewhere.


Good luck - and please report back




======================= AFTER THOUGHT ============


I just read back over prior posts. Much attention was on Injectors. Before giving up otherwise ..... have we swapped a COP in place of #1 and make sure the problem (just in case it could be an internal COP failure) doesn't move. That would be inexpensive and useful test.

 

I swapped in a new known working coil at one point. Swapped back to this after I was able to verify operation. The only other thing I have found is the hot side wires, which are on a plug by the computer show continuity to ground with the key off. Key on they are only getting continuity to power. Scanner is showing the computer infact getting over 12 volts of power also. Is there something else that controls the injectors or coil packs in any way before I splice this all back together and order a computer?
As far as changing it, they mounted the thing directly above the exhaust manifold and ac condenser as all electronics should be placed. Near heat and against a metal object...

And usually I am doing this work on other peoples cars. So I am always pretty thorough as to not waste time or their money on parts that are not needed. This just happens to be one I purchased to fix and get down the road. Ridiculously nice looking truck. But I never like keeping them becuase of the gremlins they have.

 

That would make sense. It should - in the same way the hot side of a head light bulb (or any load) would when power is shut off.


And no - to my knowledge there is NOTHING else that controls the injectors (that would selectively shut down ONE or TWO). I don't think O2 sensors can even react quickly enough to determine a single cylinder needs to be shut off. Best it can do is adjust the fuel trim for one bank if one injector is over active (leaky) or under active (plugged up / dirty).


There are several custom PIDs that could be investigated (misfire counts and so forth), but with computer suspect already I don't know if I'd trust them. Guess it could still be a rabbit trail, but I think the next thing I would try is change the PCM.

 

You are the second knowledgeable person to agree with me that the pcm seems to blame. I will order one and respond as to whether it fixed the problem or not. Or, if I find something else then I will let you know. Thank you for your help.

I have run into a second issue now. I believe any 2004 ford will be pats equipped? How does a person order a computer for one that will work?

 

Hummm. ... as I said


Guess I'm not so knowledgeable after all. Wish I could help more. I will poke around in my factory service manual, but don't recall seeing anything about that.

 

I actually towed it to a dealership near me yesterday. They supposedly are going to test the computer for me. It is probably a waste of money but if they at least get what I asked them done then I can find out what is going on with the truck.
Oh, and the pats system does need programmed. Luckily, there is a company who takes the vin, programs a computer, and sends you two new uncut keys that will pass the pats system. You get the keys actually cut at any locksmith and you are good to go. Whole deal only cost $300. Cant complain.

 

Ok so I picked up the truck today. They said one injector is stuck open and another is the incorrect injector. Evidently they changed the way they determine injector size now. Used to be color coded. So hopefully I can track injectors down for it today. Will let you know what I come up with.

 

Looking forward to knowing - and problem solved.

 

So I received my new injector set yesterday. Also installed another harness I found cheap, just in case. Not a single thing changed. Same two codes. Im truly out of ideas here except for a computer.