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03 Montero Limited 3.8L start-up tapping & misfires while driving
10-08-2014, 02:16 PM
Post: #1
03 Montero Limited 3.8L start-up tapping & misfires while driving
I have a 2003 Mitsubishi Montero Limited 3.8 liter/V-6 4x4, 156,000 miles that I bought with a problem that has gotten worse as I’ve tried to fix it. Since buying it about 8 months ago I’ve put about 1,000 miles on it, town and highway. Upon startup it randomly makes a fast-paced loud clicking noise that gets completely quite after a few seconds to 3 minutes maximum. The seller thought it was a rod knock but I didn’t think so…he wasn’t a mechanic and didn’t have it checked out by a mechanic (so he says). This clicking noise has not gotten worse however, but the misfiring that may/may not be related has gotten worse and more often. Shortly after buying Montero these lights began showing up: Check Engine, Road Slippery, and Traction Control Off. The Montero also began vibrating from something that feels like the engine is missing and/or being controlled to slow down by the ECU. When this happens I’m always going above 65 to 70mph. When I let off of the gas pedal the vibrating will stop as long as I don’t speed up again past about 70mph. When the vibration starts at high-speed all 3 lights I previously described will pop on simultaneously, or the Slippery Road and Traction Control Off will come on a few seconds/minutes prior to the Check Engine light. It use to just do this, but recently, after the high-speed spasm it will begin running really rough (missing and clacking/tapping) for short periods (or constantly) after I turn the Montero off and it slightly cools and is restarted/driven. Sometimes it runs so poorly after restart it will stall or barely move (lurching forward as misses).

After I reset the ECU (just last night) the Check Eng, Road Slippery, and Traction Control Off lights stayed off for about 5 miles. Immediately before all lights returned (almost simultaneously) I felt the engine softly miss/stumble at various times from 15 to 50mph as I sped up and slowed down, for about 3 minutes. As I pulled into driveway and stopped to back up into parking it stalled instantly, but restarted again immediately and backed up into parking. When engine was missing/rough my headlamps would mildly flicker, hardly noticeable though. The next morning upon start-up the clicking happened for about 8 seconds and then went away and it continued to run rough and misfire some.

This is what I’ve done so far:

Ran an OBD scan that told me Bank 1 Lean and Cyl 6 misfire. Removed intake and inspected (it was clean). Changed spark plugs and slave plug wires. Changed oil/filter. I disabled to ABS by removing the fuse to be sure the ECU was not slowing the Montero with ABS system. I flushed the injectors with transmission fluid (in the gas) as well as injector lube/cleaner. I’ve checked the transmission fluid and levels (clean and correct it is). I’ve inspected the vehicle for wiring chaffing or damage (such as mice chewing). I’ve changed the air filter and checked the radiator for oil/dirt. I’ve looked for electrical arching/shorts and also sprayed carb cleaner around the intake looking for leaks and listening to idle. Cleaned the MAF Sensor with sensor cleaner. After this I rebooted the ECU (or so I think) by disconnecting the battery for 40 minutes (it did reset the error lights for a few minutes but did not help any problems).

Nothing I’ve done has helped and after I replaced the plugs/wires and inspected the intake the misfiring problem and rough idling and various-speed misfire became worse and almost constant. It is slightly different from day to day. Sometimes it’s fine when cold, sometimes not. Sometimes it misfires when hot, and sometimes it doesn’t. The only sure thing is the problem is getting more prevalent and has caused me to stall a few times at lower in-town driving speeds. I’m afraid the constant misfiring will cause hard damage sooner or later.

This is what I don’t know of the Montero history: Whether or not timing belt or water pump was ever changed. Whether or not the Harmonic Balancer is good. Condition of in-tank fuel pump, seals and filter. Condition of Oxygen Sensors (however computer said they were ok). Condition of 3 Ignition Coils. Condition of Fuel Injectors. Is there any vacuum leaks that could cause this (computer said I didn’t have any though)? And is any of these relevant to my symptoms?

Ideas as to problem? The only thing that changed any traits was when I sprayed carb cleaner around intake I did get some very mild idle change for a short period but everything is tight and appears ok around intake. It was very, very mild change when I sprayed the intake down, nothing that caused it to stall or misfire.
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10-09-2014, 12:13 AM (This post was last modified: 10-09-2014 12:13 AM by Rupe.)
Post: #2
RE: 03 Montero Limited 3.8L start-up tapping & misfires while driving
I am not really familiar with this vehicle but the basis for a decent diagnosis should be pretty much the same for all with OBDII so that means you need to find out the exact codes for all systems and address them in the order they show up on a scan. Post them here for further chatter on the subject. Your "reset" of the systems via pulling the battery cables doesn't erase or reset anything except short term fuel trim and may actually cause it to run worse for a few minutes. This is where you need access to a full function scanner. You also need to sort out that noise because it may be the root of a mechanical issue and at that age I feel you will want to know if there's major $$ repairs in your future. It may cost you a cup of coffee or $100 to have a consultation with a decent mechanic but I feel it's worth it in the long run.
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