Bones1

I have a 5.4L '04 F150 with 105,000 miles on it. The truck had a slight stutter at around 45 - 50 mph under low acceleration. No noticeable problem when I punched it. It had been like that for about a year. The check engine light was not on at that point. I finally took it in thinking the plugs needed to be replaced and I had that done as well as the coil boots, not the coils.


The mechanic said that there was a cylinder 7 misfire issue that they wanted to try and diagnose. I said OK. They swapped the coil with a different cylinder and the problem stayed on #7. They then swapped the fuel injector with a different cylinder and the problems stayed on #7.


They then did a compression test. Cylinder #6 was 195 psi, cylinder #8 was 195 psi and cylinder #7 was 120 psi. At that point they recommended a new motor for $7000. They said these 5.4L engines are known for this problem and it needs to be replaced. Obviously, I am trying to avoid this.


I went to pick the truck up and it now runs significantly worse than when I took it in. It shakes at idle, it shakes significantly when accelerating. The check engine light is now on with a cylinder 7 misfire code. They said the only reason they can figure that it is running worse is because the plugs on all the other cylinders are now working correctly, so the compression problem is more noticeable on cylinder #7. I don't have a clue what to do at this point. Any help is greatly appreciated.

techrep

iTrader: (1)

did they ever swap the plug on #7 ? the compression test don’t lie if in fact they did it correctly...you can always get a second opinion... good luck

lewissa81

Does the motor make any abnormal noises? It's possible you could have a lash adjuster stuck, causing a valve to not close completely.

bart98stang

I recently had something similar happen to me on #4. My truck, '05 SCREW had 127, 7xx miles and there was a miss under load at about 40-65 mph so changed all 8 coils. Still had the miss and attempted to replace the plugs. I broke 7 of 8 and the last one couldn't get out. Took it to a local Ford dealer and they had to remove the head to get the broken piece out. Upon removing the head they found #4 piston was cracked and the wrist pin broke causing the rod to separate from the piston and had 2 bent valves and one of the valve seats had a nick. They gave me 3 options. Reman motor with install, junk yard motor, or replace the pistion, rings, rod and bearings on #4 so I went with the piston replacement. Not saying this is what's wrong with your truck but with the coils and plugs just replaced and it's running worse......... Also, since the motor was already torn apart I had them replace the chains, VCTs, phasers, tensioners and guides.

Bones1

Thanks for the responses so far. To answer your questions, they think they tried swapping plug #7 with a different one, but the response did not give me confidence that they did.

The motor does not make any abnormal noises, it is just running very rough.

Houbezra

Check for power to cylinder 7? just swapping the parts is assuming there is power at that pigtail would rule that out first even check the resistance in the wire. stick a scope in there to check things out. replacing the piston itself isn't a big job to be honest done it a couple times as a quick fix for clients that cant afford the replacement option. If i were to rule out electrical my next step would be to peel off the valve covers and look at the valves and springs then start digging in deeper like removing the oil pan for a good look inside. Do you have or had a exhaust manifold leak on that cylinder? letting that go for to long can burn a valve out.

Newfiedan

Check the wiring for that cylinder when I did my plugs I had the rubber boot for the plug move down and spread the pins in the male plug end for the coil causing a random misfire when I swapped my plugs. Check that first. I had to remove the pins and fix them with a sharp pick.

Bones1

Is it possible that a plug could be bad out of the box and be causing this? I just can't figure out why it seems like I have a different problem after the plugs were replaced. What was a slight stutter at a certain speed is now a consistent shake and a cylinder misfire code.

F150Torqued

Bones1: Sorry about your problems - hope my experience I can help. I had the IDENTICAL problem with my 04 5.4L starting about 120,000 and I fought it for two years / 60k mi. Sure I spent $2500 replacing parts and 200 hrs labor swapping, changing, talking to mechanics and reading posts. Many things would help - some make it worse but nothing fixed it. UNTIL, one day I decided "IF THE "F*?#$^@&" CARBON BUILDUP AROUND THE SPARK PLUG IS ENOUGH TO TWIST THE ENDS OFF UPON REMOVAL - HOW THEN CAN ONE EXPECT TO SCREW A NEW PLUG BACK IN THAT SAME DAMN HOLE WITHOUT DAMAGING THE SNOUT ON THE NEW PLUG OR "FRACTURING" THE CERAMIC INSULATION INSIDE THE SNOUT?" I had never read a TSB or post talking about this possibility. So I bought a (third) set of new spark plugs (Motocraft SP515 this time) and spent $19.99 on a set of steel thread brushes (similar to bottle brushes) with a "T" handle from Harbor Freight. While replacing the plugs, I took one of the steel bottle brushs (about the size my little finger) and cleaned the carbon out of the spark plug holes until a carburetor soaked rag would come back perfectly clean!! If not, I'd burnish the **** out of that hole again. When I got through, the new spark plugs screwed all the way down to the seat with my fingers just like putting them in a new engine. INSTANTLY - BINGO - perfect startup, idle, and about 8k miles later without a single misfire. My OBD II diagnostic tool indicates ZERO misfires on all 8 cylinders in the last 10 drive cycles. At 197,000 its a perfect pleasure to drive - gradual acceleration is perfect until it shifts down and goes on like it is supposed to!!!!


I believe MANY MANY people on the forum are damaging new plugs on install because of the same carbon that seized the old plug and broke it off coming out. This could possibly be what happened to your number 7 plug. If it was seized up bad and the mechanic removed / reinstalled it again to check compression or whatever - it could have cracked the ceramic inside the plug leaving it vulnerable to arcing over inside. I'm pretty sure this is why my first TWO spark plug changes did nothing but make the random misfire or intermittent misfire just move to different cylinders.
This is a fairly simple and cheap thing to try - and it made logical sense to me even though it sounds so simple as to be stupid.
If you try it, I would love some feed back. I'd like to know if this silly simple step is really what cured my annoying random misfire after having changed COP's, VTC Solenoids, O2 Sensors, an Injector, Boots ....... and a ****load of other stuff chasing the problem.
Good Luck.

lewissa81

I think there are a lot of things possibly causing this. It is a little odd that it's running worse now. I would get a second opinion from a known, trusted mechanic. The first one could have messed things up unintentionally. For instance, if he cross thread the #7 plug then the compression tester may not have had a good seal and given a false reading. I'm not saying that's what happened, but you never know. Definitely get a second opinion before you either shell out a bunch of money, or drive yourself crazy by speculating on possibilities.