High RPM faint misfire, unsolved mystery

[09_misfire]

I am nearly at my wit's end with my '09. 2.5i non-turbo.

 

I bought it in January 2016 with 203,000 on it (All highway,  original owner,  full maint log, good shape, ran great).

 

Noticed it had a significant oil leak from both heads (head gaskets, external oil leak)

 

Pulled motor this fall, resurfaced both block and head with the manual block-sanding method, installed new gaskets, torqued as per specification, reinstalled motor.  Noted oil on plug wires,  replaced valve cover gaskets and got cheap auto-parts store wires* (we'll come back to this shortly), installed new NGK iridium plugs.  Reset valve clearance to stock (was slightly loose by a few thou on most valves)

 

Shortly after getting it back together it got a flashing MIL on hard acceleration (misfire codes  on cyls 1 and 2 (P0301, P0302)).  Didn't really feel the misfire however, it is very faint and only noticable under full throttle,  light throttle to redline and you can't feel it,   sometimes the mil will flash on part throttle pulls, but will ALWAYS on full throttle pulls.then the light goes out,  only comes back if I push it over 4000 and over 1/2 throttle,  enough of these will result in it staying on and getting the flashing cruise control (perm codes set)

 

Figure well the coil is probably ancient,  I just changed the wires, with the HG job, so lets replace the coil.

 NO CHANGE

 

So I tried a new set of plugs (NGK iridiums)

 NO CHANGE

 

So at this time I'm figuring that the ignition system is completely replaced (with the exception of the main ECU), I turn to fuel.  

 

clean out MAF (non-chlorinated brake cleaner + compressed air)

 NO CHANGE

 

This one has an in-tank filter instead of the nice easy to replace one of the pre '05 models, so it was cheaper to get a junkyard pull full pump assembly instead of the fuel filter itself,  so I got a pull from a car with 78k miles and install it,  

 NO CHANGE

 

So I figure, maybe the one I got has a clogged filter, so I rig up rube goldberg fuel pressure gauge I can watch while driving,  

 52 PSI all the time, even at full throttle pulls when the MIL flashes the misfire blues..  so it's not the pump or plumbing up to the engine.

 

Googling seems to indicate a remote possibility of the timing belt being off by one tooth, so I drop the coolant, pull the radiator, and pop off the covers and double check, nope it's SPOT ON, and the tensioner is fine (not leaking)

 

So googling some more seems to indicate all but OEM or NGK plug wires are garbage,  so I order a NGK FX-101 set and install them (fits great),  

  NO CHANGE

 

Running out of things to replace.

 

Only thing I can think is left is a possibly burnt valve, or a bad pair of injectors (that are flowing less than they should)

 

Using my OBD-II tool (Obdlink-SX and OBDwiz) shows the misfire counts are highest on cylinder number 1, and about 1/4-1/6th as many on cylinder two,  never any on cylinder 3 or 4.

 

Was going to swap the 1&2 injectors to the 3&4 position next to see if the problem follows it..

 

Anyone else have any suggestions?    I don't have a leakdown tool, but I'm sure amazon does,  though the engine cranks evenly, so if it was down on compression it would typically be noticeable during cranking from the weak cylinder..

 

-- frustrated....  I really miss my '98 OBW with the 2.5 NA quad-cam

 

 

 

[1 Lucky Texan]

kinda want to ask about the plugs - are they the correct part number? did you check or adjust the gap?

 

re-check for oil in the plug tubes?

 

looks like you are very close to needing a timing belt system service - kinda wonder if cam timing could drift enough to cause problems if the tensioner is weak?

[Fairtax4me]

Dynamic compression is different than static compression.

Static compression is what you'll measure when cranking the engine during a typical compression test.

 

Dynamic compression is measure while the engine is running. Testing dynamic compression can show you if the compression in one cylinder is dropping at higher RPM due to a valve problem.

 

Typically high rpm misfires will be due to fuel starvation or incorrect valve timing, which can be caused by several things.

 

I would pull the valve cover on that side and readjust the valve clearance. Loosen them up some, especially the exhaust valves.

 

Another thing I notice is you say the fuel pressure sits at 52 psi all the time? Even at idle it's still 52 psi? That's indicative of a stuck or clogged fuel pressure regulator, or the vacuum hose to the regulator is broken or no longer attached to the regulator or intake manifold properly.