2003 Mitsubishi Montero LTD P0300 Random Misfire & P0660

[jotill00]

Hi All,

Back in May, I purchased a used 03 Montero LTD with the 3.8 engine broken with the intent on fixing it up myself. I tore into it head on and found the bank 1 timing had jumped by 1 tooth due to a faulty tensioner. I replaced the tensioner and reset timing hoping nothing had done wrong in the cylinders, but it had. It did fix the awful clanking the engine was making, but not the P0300 code I was seeing as well as a backfire once it was warmed up. After leakdown testing, cylinder 3 had no compression and cylinder 1 had low compression.

I purchased a used cylinder head and had a local head shop fix it up for me for a fresh install. After reinstalling, the P0300 code is still around with the backfire as well. Additionally I have a new P0660 code for the intake manifold tuning valve control circuit open bank 1 . What direction should I go next to try and resolve these two issues? Do you think these issues are connected? Is the o-ring on my intake surge tank bad and need to be replaced?

Some helpful details:
Butterfly valves were completely removed by previous owners.
I've replaced the coils and spark plugs
The timing is confirmed to be in time with the proper installation torque for the tensioner.

 

[jotill00]

Update:

I ended up pulling the surge tank off and messing with the plug wires on the passenger side/ RH bank. I replaced them since that was the only thing I hadn't touched on the ignition system. I had already replaced the coils on the LH bank. This solved my misfire code and backfire, thank goodness! The other P0660 code was simply a plug that I had missed on the surge tank vacuum solenoid.

That being said, I still have a bit of an issue. There is some valvetrain noise coming from that RH bank still. I've taken it to a shop, but the only thing I can think of that would still be wrong is the hydraulic valve clearance adjusters. The gentleman at the cylinder head shop mentioned something about the seals not being in good shape from the old head.

Looking around on the forums, it seems there's a procedure for priming the hydraulic valve lash adjusters while its in the vehicle. I'll give that a try and report back.

 

[Michael Brown]

These engines are known to have some valvetrain noise, but it wouldn't hurt to replace the valve adjusters if priming doesn't work.
There is a tool to do this on the Mitsubishi engines without removing the valve springs.

https://www.amazon.com/Schley-Products-Hydraulic-Lifter-Removal/dp/B002YK75CU

You also may be able to quiet the noise by increasing oil weight to 10w-40.

Beyond that, you may find something in the FSM in my signature.