2002 F-150 misfire

[GregH]

After our drivability tech tuned up this truck, he noticed a misfire on #6. He had just installed plugs and coil boots and did a BG flush on the induction system. Truck has a 5.4L, and the mileage is about 130,000 miles.

 

Misfire is constant on #6, dropping about 15RPM during a power balance test. Noid light tests on the coil and injector produce a nice flash. Plugs, injectors and coils were swapped one at a time between #5 and #6 with no change. Compression tests showed about 125-130 across the entire right bank. Running compression was about 110 on #6 and #5. Cylinder leakdown was just above 0.

 

We're unable to run an injector flow test - the IDS tests the first injector and then shows "ID" for the rest of the injectors - and does not flow them. The IDS behaves in the same way installed on a like vehicle.

 

Sometime during testing, we noticed that the injector stopped receiving a signal to fire from the PCM. Wiggle test the wiring around the A/C accumulator, and there was no difference. Hooked up the breakout box and checked the signal at the PCM - only an intermittent signal was present on #6 injector. Ohmed the wiring - 0 ohms. Load tested and we can light a turn signal bulb solidly off of both injector wires. Replace PCM - pulse came back but dropped off again shortly thereafter. Of course, it was then that we figured out the PCM was going into FMEM and killing that injector to save the catalytic convertor... Red herring...

 

So, what are we missing? We've got good signals to the injector and coil. We've got good spark - we can lift #6 coil and hear the arc. Base engine seems to be fine. Ruled out the injector and plug through swapping. What's left?

 

We have not verified if #6 can flow fuel. That test is not functinoal in the IDS. None of us have the tool used to hear an injector firing while the engine is running. If there is no fuel coming from #6, then it would have to be in the fuel rail - and that looks clear. #6 plug usually comes out a little fuel fouled.

 

We have not verified if #6 coil and injector fire at the right time. A loss of timing on this scale seems unlikely without inadvertently switching the wiring around - but then we'd have a mirror problem somewhere else. The problem seems localized to #6.

 

No codes are in memory other than P0316 and P0306.

 

The problem is constant whether it is hot or cold. Test drives do not clear up the problem...

 

Any help would be appreciated...

[GregH]

An additional test we did while BOB was hooked up was to light the turn signal bulb using the wiring to the #6 ignition coil. It lit nice and bright.

[BrunoWilimek]

I would wonder if one of the valves was not opening. It would still have compression if the exhaust valve did not open, but as no exhaust could escape, it would be like a plugged catalytic converter, thus accounting for the wet plug.

[Matt Saunoras]

i had a broken intake valve spring on a 5.4 3v. it was a few years ago and i can't remember exactly the symptoms other than an occassional idle misfire. anytime anyone mentions a 3v misfire that always pops into my head

 

whoops. missed that 2002 part

 

seen valves sticking on 2 valves but it always showed up on running compression

[Brad Clayton]

Quote:

After our drivability tech tuned up this truck, he noticed a misfire on #6. I gotta ask how it ran before it was "tuned up" He had just installed plugs and coil boots and did a BG flush on the induction system. Truck has a 5.4L, and the mileage is about 130,000 miles.

Misfire is constant on #6, dropping about 15RPM during a power balance test. Noid light tests on the coil and injector produce a nice flash. Plugs, injectors and coils were swapped one at a time between #5 and #6 with no change. Compression tests showed about 125-130 across the entire right bank. Usually, a healthy gasser will be above 150 psi and most of the time right at 180 psi. Running compression was about 110 on #6 and #5. Cylinder leakdown was just above 0.

How much crud and dirt is on top of this motor? Hoping you meant left side on the compression testing. The running test seems high and the manual compression seems low. But that's neither here nor there. I would have to assume this engine ran fine before the service work.

I had a very similar problem back in the summer and it turned out to have a bent exhaust valve. It was only a little bent. This was pinned down by applying shop air into the cylinder with the follower fingers removed.