Hi all.

The problem started only recently, but it's progressively getting worse. When cruising along about 75-80 mph on level ground, the engine runs fine.
If the load increases (press harder on accel, going uphill, etc.) a ping starts to develop. Again, only at highway speed... typically in 5th gear
If the hill is long enough and I hold it in 5th gear, it'll ping like crazy and eventually Cyl 4 will misfire, triggering the MIL, disabling the ESTCAS, and causing a strong vibration until I let off the accel a moment later.

Since the timing is ECU controlled, I suspect the problem is caused by the cracked exhaust manifolds (that I've had for a solid 18 months now and I still can't afford to replace) but I'm not sure since it only seems to occur if I'm driving 75-80mph in a high gear.

My thoughts:
Under a sustained heavy load in high gear, the large volume of exhaust gasses and lack of adequate back pressure caused by the cracks in the manifold allow abnormally faster evacuation of the gasses causing cyl 4 (where one crack just happens to be near) to eventually misfire from abnormally lean mixture.

Other info:
118k miles. I use only premium fuel. No other ticking/pinging or and other problems at all with the engine.

Am I way off? Any thoughts, experiences, additional insight?

Thanks

 

now try this empty that tank of gas tank, and run regular unleaded. see if that make a difference. usually this pinging will occur when you use a higher grade of fuel other that specified.

 

Gen III Monteros call for 92 gasoline.

 

Yeah, I only use 92.
I'm taking it to the dealer on Monday. I took it to them last Wed, but they could not get the scan tool to communicate with the car. They are telling me it'll be like a 4 hour diagnostic to fix what's wrong with the interface and diagnose what the problem is.

 

Are you planning on replace the cracked manifold before bringing it to the shop. That sounds like the logical place to start with repairs. For all you know the shop may spend four hours diagnosing your problem and end up telling you your manifold is the cause.

 

True, and that would have been the logical thing to do, but I don't have the tools or the time or a garage to tackle the manifolds myself. Not to mention, if one of those retaining bolts snapped off, I'd be screwed.
I thought about taking it to a local repair shop for the manifolds only, but I wanted a mitsu tech to make sure it was tuned right. That's how I arrived at the decision to take it to the dealer to have them do it all.... I hate it, but I really have to.
I will be sure to post what the findings are

 

Good Luck
I've had to take the hit of dealer prices a few times too.

 

Well, truck has been in the shop for a week and they haven't even gotten down to diagnosing the real problem.
After 2 hrs of diagnostic, the service dept called last week and said they could not get any data from the onboard computers. Long story short, I've been driving the truck for a year without the LCD screen in the RV meter because I thought the LCD died one hot day in the sun. Since the buttons still made beeping noises, I thought only the LCD was shot and removed it hoping to find a replacement. It turns out the whole unit must be bad.

New ones run about $800, so I found one from a salvage yard in Pittsburgh...
Will update again once it's installed and we can begin getting down to what's causing the pinging/misfire...