Dealer installed new plugs in my 2004 5.4 F150 ($ 1,300, broke 6 of 8 plugs, replaced 4 coils). Truck ran perfectly fine before "service" (134K). Truck now has chronic lean condition on driver side (P0174) and misfires on cyl. 1. Dealer says it needs a new engine. Engine now has no power (huge induction noise), and sounds like it's choking at WOT.

Swapped coils on Cyl. 1, still misfires. Checked wiring harness, resistances are good, no shorts. Plug looked slightly wet. on Cyl. 1. Compression on cylinders 1 & 2 are both low at idle (100 to 120) but rising to 170 at 2500 rpm).

Suspicious of VCT system (has cam phaser noise for sure), but no codes are showing, unless I disconnect the VCT solenoid. Could be a plugged Cat. on passenger side, but what is the root cause, and why did this start after the "service"?

 

sounds like they dropped debris in the spark plug hole and you have valve damage because of that. Find a nice junkyard motor with low miles.. change the plugs on an engine stand before you put it in.

 

A bad valve caused from debris during the plug change would not explain the lean condition on the opposite cylinder bank though.

If the VCT is not functioning correctly it could restrict the air coming into the engine which would lower the compression test results. Both cylinders 1 & 2 had the same compression tests (what are the odds of debris in two cylinders side by side).

 

the missfire is causing the lean DTC...you need to do a cylinder leak down test. basically you put air into the cylinder with it at TDC on the compression stroke. Listen where the air is comming out(intake, exhaust, crankcase). May have a damaged valve or valve spring. A cam phaser issue will make the whole bank missfire.

dont forget a fuel washed cylinder from missfiring can also lower your compression reading

 

Good idea on the leak down.

The truck never misfired before the plug change (in regards to fuel wash idea) It also behaves like it has more problems than a single bad cylinder. Struggles to maintain 45 mph. At low throttle positions it's actually quite smooth and quiet. Dig into the throttle and major stumbling ensues. Longterm fuel trim shows very lean on driver side (+28%), but no misfires on this side? No smoke on startup, clean exhaust.

 

a few other things you can try after the leakdown test.
if you have a scan tool monitor FRP(fuel rail pressure) and see if it drops down when you lose power.
also use the FRP data to check if the system holds fuel pressure with the key on engine off. if it drops of quikly check for a stuck open fuel injector.
Try disconnecting the exhaust at the manifolds and retry your compession test, may have a plugged off cat.

 

what plugs did they use???

 

If the truck ran perfect before the service why did they change the coils?

 

Fuel Rail Pressure is good. 40 PSI and fairly steady according to scanner (also rail pressure would cause lean condition on both banks).

Not sure why they needed to change so many coiis. I just bought the truck and took it in for the infamous first plug change.

 

I'll check the rail pressure on shut off though. One or two bad injectors could be a possibility I suppose.

 

Sure sounds as if you are the victim of a dealer that has no clue what they are doing. Really hate that for you. Sounds as if they have really messed it up and started throwing coils at it.

 

Yes I'm not too impressed with the local Ford dealer.

Some more information too:

Changed upstream O2 sensors to see if this would help the chronic single bank lean condition, no change. Spark plugs are Motorcraft.

Could it be a plugged converter in passenger side (this is side that has the new miss) causing lean conditions in the opposite bank?

My assumption is the VCT is working ok since it does not throw codes (it's a closed loop PID positioning system). The VCT solenoid looks good (clean) and shifts when energized. I don't have a scanner that can read the VCT PID values though (any suggestions on a PC Based scanner?). But I think if there was a malfunction in the cam positioner PID loop, it would throw a code.

In fact if you drive gently, the truck has no codes at all.

 

Just had another look at the Ford servicing notes and mechanic replaced all four coils on passenger bank because IDS cylinder balance test indicated missfires on Cyl. 1 thu 4.

 

Has anybody looked at the CMC valve system? If it runs decent at low RPMs, it might be the drivers side is stuck partially closed and it may also be that the tech managed to disconnect the system on that side. It will have no power at higher RPMs because the engine can't get any air on that side. It'll also run like major crap because of the unbalance of air going into each side of the engine. I would assume the o2 sensors and the PCM are going to read this a s lean condition as the PCM is going to cut the fuel down considerably. Something to check anyway.
CMC= Charge Motion Control valve. It is an electronic device, a flap as such, at the end of each intake runner that speeds up the intake air at low throttle to create a tumbling effect so that the air fuel mixture is more easily and completely burned.

I'd also have somebody with a bore scope to look at the cylinders before spending the bucks for a new engine.......which it sounds like you don't need. Sounds more like you need to find a tech that has a clue about Tritons.

 

Yeah I've been thinking about the CMC as well, since it would indeed give large air imbalances as you suggest. So the driver side runs lean, would this not mean it's stuck open (too much air), and maybe passenger side is stuck shut (not enough air at WOT)?. I assume you energize the valve at a certain throttle setting to open up the secondary intake runners? I'll check the linkages. This is the one item that does not have position feedback (I don't think) so it could be stuck and no codes are tripped. Good idea.