Hi all - I've been lurking in the forum since July when I purchased an '89 Montero LS, 3.0 V6, Auto and excited to be part of Montero group. The truck is mostly original and seems to be in great shape, both cosmetically and mechanically. Some very minor fluid leaks (as to be expected) and a shot passenger window motor seemed to be the biggest issues when I purchased.
Apologies for the length of the post below, but I wanted to give a thorough explanation of what I'm dealing with, in hopes that somebody has had a similar experience or troubleshooting ideas. I have some working knowledge, but am far from an expert. Any and all thoughts/ideas are appreciated. Thank you!
After purchasing the truck and a few days of daily driving without issue, it randomly died while I was leaving my neighborhood. No warning signs, no sputter, just went from running to nothing with all dash & accessory lights coming on. I pulled over and attempted to restart, truck cranked strong but wouldn't fire. Tried every few minutes to get it started, repeatedly same strong crank, but no fire. This continued for ~30 minutes, then without any apparent change/reason, the truck cranked and fired right up as if there were never an issue, and I drove home.
This has been a reoccurring issue for the last few months. 9 out of 10 times that I start the vehicle and drive, I have no issues -- this includes starting from cold, starting from warm, quick trips with frequent starting/stopping/restarting, and long road trips 250+ miles -- when it runs, it seems to run really great.
I haven't been able to pinpoint when/why the no-start and/or stall is occurring, but it has happened approx 20 times and has the same characteristics every time -- either won't start (more frequently occurs when warm vs cold) or it will start normal but die within 10 minutes of driving (I've never had it die once it's been running for more than 10 minutes, but that could just be a coincidence). While driving, it doesn't seem to have a "normal" time to die, meaning it's happened while accelerating, decelerating, while sitting in park, and while sitting at a stop light. After no-start/dying, it has always eventually started, sometimes it takes 5 minutes of periodic cranking, sometimes it takes an hour, but so far it has always started without me "solving" a problem and has no running issues thereafter.
After a searching service manuals and online for answers, I brought it to Mitsu for diagnostic. They were able to recreate the stall once, cleaned some corrosion from a connector and tightened contacts at the power transistor and sent it home. It died the following day so I sent it back, and in the past two weeks they have not been able to recreate the problem (most likely due to a lack of time/effort to try and recreate without a better road map on "when" it is occurring), thus no further diagnostic. I picked up the truck yesterday, ran errands, several start/stops with no issue. Drove to the gym this morning, an hour later it wouldn't start, and 30 minutes after that I was back on the road.
Any thoughts on what this could be? It seems like it must be electrical, but doesn't seem to be a battery, alternator, bad connection, etc. I've seen suggestions to replace the ECU on threads that have similar (but different) symptoms, but hoping somebody might be able to narrow this down before I implement guess and check. Thank you.
The things that come to mind are: ECU Power transistor (though I would expect this to fail completely) Fuel pump or fuel pump relay (would need to check pressure to verify) Distributor (IIRC there is something different about the 89 vs 90 vs 91 distributors)
There is a 89 Diagnostic Manual available. There are some thing different going into 90. But it might also give you some items to check.
Mitsu # 6 - 98 6G72 Montero Sport, R D Lock, 31x10.5
I just popped open the ECU and didn't see any obvious signs that it has gone bad. Connections and pins look good and no signs of any fried spots on the board. I was able to confirm that a "late click" after turning off the engine is coming from the ECU (link to video), can anybody confirm whether this is abnormal? Thanks.
I replaced the ECU with a re-manufactured unit from Cardone, but unfortunately the symptoms continue. No issues on Day 1 while running errands and test driving in the neighborhood with frequent stop/starts. Day 2 after ~20-30 minutes of driving the neighborhood with stopping/starting every few minutes, I started up as usual, put into drive and began to pull away, at which point it killed and all dash lights illuminated. I tried to re-start for the next few minutes and it would crank strong, but no fire, same as before. I tried to unplug/replug the ECU, but that didn't result in any changes. Came back an hour later and still wouldn't start. Went back this morning and it started right up, drove 2 mins home, and stopped/started several times in front of the house with no issue.
Both new and old ECU have the same delayed click (as shown in prior video) after disengaging the ignition/starter, so I'm assuming this is normal.
I'm guessing there isn't much wrong with the Air side of the equation.
Fuel - On a "No Start", do you have much of a raw fuel smell at the tail pipe? When turning the ignition "on", but before "start", can you hear the fuel pump relay click at the passenger side kick panel? What about the fuel pump?
Spark - On a "No Start", can you check for a spark at one of the spark plugs?
Mitsu # 6 - 98 6G72 Montero Sport, R D Lock, 31x10.5
MarkG, I appreciate the continued input, sorry for the delayed response. After the ECU replacement didn't improve the problem, I went back to the original ECU and replaced the Ignition Coil and Ignition Coil Module. It's been 5 days of frequent driving/testing, ~100 start/stops without any issues. I'm not allowing myself to be completely sold yet, but starting to think this was the necessary fix.
I had the same problem with my 89, turned out to be the ignition module harness. Even messing with the contacts the way the FSM said to, I wasn't able to fully defeat the problem. Ordered a new connector ($14) from Rockauto.com and has been trouble free the last 3 1/2 years. The part is from Standard, part # S745
89 SWB, V-6 5SPD, OME Shocks, 16.5X37's, 2"BL, SR axle, Gen2 brakes, Lincoln w/Superwinch
Thanks for the tip, I’ll be ordering a new connector tomorrow. The replacement coil and module seemed to help (had a good two weeks without stall), but now it’s happened a couple times again. Will follow up with an update after install and test driving.
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