Misfire under load.

I don't trust the code reader! I can go out to any ford I own and clear the codes and scan and have no misfires counts showing. Start it up and idle. Pull either coil connector or injector connector off one at a time for 2-3 cylinders for 10 seconds or so each.
Scan again and THERE WILL BE misfire counts.
Done this too many times.

In your current situation I would get it in drive at idle (safety precautions of course) and remove one coil connector at a time to see which ones make a big shake and rpm drop and which ones make less or no difference.

This will be the most telling test you can make now.

OK guys. It feels like day 792, and I keep doing the same thing. LOL.

In all reality I spoke with a coworker who used to be the head tech at a Mercedes garage, just to get more input and ideas. Not sure if this helps or not. He suggested as it only happens when load is present at stop to get the truck to operating temperature, crank the A/C, and turn the steering wheel lock to lock to load the system with power steering and A/C and see if it drops in RPM and stalls, or not. His though was that if it did it would clearly indicate an ignition issue, if not he was thinking idle air control, or that the PCM is not detecting load from the transmission. I did this and RPM dropped minimally if at all.


Next I smoked the engine again (through the brake booster hose) just to make sure, and nothing, except out the air intake opening. I then went and while watching the live RPM on my scan tool started and let the truck come to temperature, then disconnected each coil 1 at a time for about 45 seconds, then let the truck rebound and went to the next. All 8 coils responded the same, none more or less than the others.


Next I took one of my Motocraft coils that had .9 ohms resistance between the 2 pins, and started with cylinder 1. Swapped it out, started the truck and placed into R, RPMs dropped to about 570 with strong vibration again. Removed the Motorcraft and reinstalled the new accel coins and went to the next cylinder. Did this for all 8 cylinders, with the same result on each cylinder.


I cannot figure out what is happening. Can any body advise what your RPM's are at operating temperature, at stop in drive or reverse? Just for comparison.


Any ideas.

What about the throttle body itself or egr ports. Ok you've done your homework, eliminated the coils and wires to them. Are the throttle body and Egr both clean and unclogged? You got one of the tougher diagnosis here, but you'll get it. Does your idle problem happen hot or cold? Are you running rich or lean on any cylinders? Theirs been so many posts, I've lost track. Any one else want to jump in? I'm thinking either a small intake leak, or plug in egr, or something with the throttle body or port. You said smoke from throttle body? Just the butterfly, that's normal. Did you make sure your air filter housing and maf sensor are clean and tightly mounted? Considering where you started in post 1, it's amazing your this good now. Any body else want to give it a whack?


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1955moose said:

What about the throttle body itself or egr ports. Ok you've done your homework, eliminated the coils and wires to them. Are the throttle body and Egr both clean and unclogged? You got one of the tougher diagnosis here, but you'll get it. Does your idle problem happen hot or cold? Are you running rich or lean on any cylinders? Theirs been so many posts, I've lost track. Any one else want to jump in? I'm thinking either a small intake leak, or plug in egr, or something with the throttle body or port. You said smoke from throttle body? Just the butterfly, that's normal. Did you make sure your air filter housing and maf sensor are clean and tightly mounted? Considering where you started in post 1, it's amazing your this good now. Any body else want to give it a whack?


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Hey 1955moose, I just cleaned the throttle body and the MAF two days ago. I am not sure what you are referring to for the egr ports. I will look that up. It runs fine at cold which I mentioned to my coworker and he said that it could run better at cold because it is getting a richer mixture than when it is at operating temperature. I am not sure how to check if I am rich or lean on the cylinders directly. I can monitor the long term and short term fuel trims, but I dont know that answers the question. New air filter about 400 miles ago, housing is tight. Thanks again for all the help!

My truck will pause and sputtrer when cold. I tried the fix things, at 280 k. New coils and the works. It may be in the cats.??? a simple clog will do it. I cut Mine out of the system.

Easiest way to see if your egr port is clogged or partially clogged, is to remove hose from EGR valve, have engine warm, apply vacuum to Egr, motor should stumble badly, and want to die. If it doesn't do this, the port from the Egr through the intake is blocked with carbon, and will need to be cleared out.

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Okay. Today I had a mechanic buddy look at it, and we were still unable to find a specific point of failure. The vehicle is not misfiring. The oil pressure at hot idle (199F) is 23-25 and drops to 18 when placed in reverse or drive, above the modified 15 psi that ford now recommends. Fuel pressure is in spec at 65 psi. He did find an exhaust leak at the manifold and the connector that bolts to the cat on the passenger side. He also mentioned that it is running high on NOx/or Hydrocarbons, causing it to run slightly lean. Still no CEL or codes, he mentioned that he was wandering if the torque converter could be causing this issue.

2008 Expedition XLT EL, 5.4, 196,000, 5W-30, New Motocraft vct's, Motocraft S509 plugs, coils, air filter, battery.
Just to recap the problem is at hot idle, in gear when the truck downshifts for a stop it will drop low on rpm's to low 500's causing the truck to shake like subwoofers are on.

Any ideas?

Is there some type of solenoid or sensor that compensates/maintains idle when in gear?

aagitch said:

Is there some type of solenoid or sensor that compensates/maintains idle when in gear?

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Hello aagitch,

Thanks for your response. Not that I am aware of, I am currently at a loss.

Short of vacuum leaks, the only thing I know that will cause those types of conditions is the air bypass valve sticking. Maybe you could take it off and clean it out well with carb cleaner and work it back and forth or pick up a use cheaper for junkyard or a cheap one off of eBay.
I guess it's possible for a flat spot or a low fuel signal from the throttle position sensor but I doubt it. You should be able to monitor live data on a scan tool and maybe see more.