My 03 montero sport has been fairly problematic the 3 years ive owned it. Got a great deal on it, knowing it was neglected and needed some attention. I ended up having the engine rebuilt 12k miles ago. Then a head gasket blew(i think the rebuild kit was cheap chinese stuff but i was too naive to ask at the time.) During (and before) all this work the vehicle always had this pesky P0300 that would pop up ONLY if i brought the RPM up toward the 5k mark. LIke clockwork, the code would arrive about 5 minutes later. Now the problem is no longer intermittent and the code arrives no matter how hard i drive it. Does this sound familiar to anyone? I'll be removing the plenum today for plugs/wires/plenum gasket/fuel filter replacement. If anyone has any suggestions for troubleshooting while the plenum is out PLEASE LET ME KNOW!!! I will have the plenum out of the vehicle for a week give or take.
***update*** i found oil in two of the spark plug tubes covering the bottom of the wire boot and the plug. The tube seals look totally new and i know they cant have more than 12k miles on them so i dont know what to do about this.

 

I'm also concerned about the cylinder bore from the rebuild is effecting the air fuel/ratio to the point of misfire? I spoke to the dealership, there are no software tweaks they can perform to modify the fuel trim etc..

 

What exactly do you mean by this?

 

The cylinders were bored out during the engine rebuild which makes the engine larger in terms of cubic inches. The computer in the vehicle is fine tuned to deliver a very specific air/fuel amount. I guess i'm concerned if the compter cant compensate properly and causing the engine to run lean...???

 

I wouldn't worry about that. Engine management computer adjust amount of fuel added to the combustion mixture on the fly based on how much unused oxygen remains in the exhaust stream. The range of fuel ratio adjustment is from -25% to +25% relative to the "normal" or expected one before the computer throws ether Rich or Lean codes. Unless your cylinders got bored to over 25% extra size (not likely), that would not affect the fuel/air mixture at all. There are likely other reasons for misfire code. Pull the freeze frame data for P0300. I'd rather see that data first before trying to guess/estimate the underlying causes.

 

Unfortunately, i have the plenum off now and the battery removed so the freeze frame data is most likelt cleared. I'm waiting for new plugs, wires,plenum gasket and fuel filter to arrive and once i get these parts installed, if the code comes back i will post the results. Also HunterD i see you're in washington..You should just stop by Oroville and have a look at my rig, I'll buy you a beer.

 

 

You couldn't possibly get any further north and still be in Washington, can you I's tempting, lets see what happens when you can get the codes retrieved.

 

sounds good. parts come in today. I found oil down in cyl 3-4 plug wells. new tube seals. came with the head gasket kit 7k miles ago. i tightened down the valve covers a bit more hoping the seals will make better contact with valve cover. also found an injector connecter unplugged and i doubt it came loose when i pulled the plenum as there is nothing under the plenum to grab or snag that wiring..?? we will see. Is there any way to check the timing other than visually look at the timing marks?

 

Having an injector unplugged could be one of the contributing causes to getting those codes prior to the disassembly.
If you are getting oil in the plug wells with new seals - remove valve covers and check the sealing surfaces to make sure you don't have a piece of old seal stuck there on the mating surface creating a gap and causing the leak.

I agree with Larry - run a full compression. With the plenum off, it is the best time to do it.

As far as checking timing, the only way to do it is to visually inspect alignment of the marks on crank shaft and both cam shafts. Make sure you have a small mirror and look perpendicular to the belt (in line with the teeth on the gear) for he marks aligning with the ones on the engine case. Just eyeballing it from the top will not work due to parallax error.