NOT Firing on all cylinders - Gen 2.5

[tyty13]

Could be a crank sensor failing form the crank sprocket issue before .
http://easyautodiagnostics.com/mitsubishi/3.0L/crankshaft-position-sensor-test-1

 

[nwoods]

Okay, I got the news from the autoshop, and its not good news.

Reading the following three codes:
P0120 - Throttle Position Sensor http://www.autocodes.com/p0120_mitsubishi.html
P0335 - Crank Position Sensor (hard fault - will not clear) http://www.autocodes.com/p0335_mitsubishi.html
P0301 - Misfire on Cylinder #1 http://www.autocodes.com/p0301_mitsubishi.html

I guess the good news is that it appears the timing belt didn't slip a notch. Bad news is that at the very least, I have to do the tear down to water pump level again and replace or fix the crank position sensor. Maybe.

The major issue is that they pulled the spark plug for Cylinder 1, and the spark plug was heavily fouled, and the porcelain was BROKEN OFF! The mechanic then ran a compression test, and instead of the factory recommended 171psi, they got 50 psi. NOT GOOD.

I am very hopeful you wise and wonderful Montero maestros can offer a plausible theory other than the need to replace a holed piston, broken piston ring, or bent valve.....


Here is one possible theory:
Per the linked narratives on the P codes, the signal plate (timing plate?) behind the crankshaft gear could be bad. This is very possible, as the original one was broken when we did the tear down initially. It was replaced by a new, used unit from a donor engine that TyTy13 had. Also, the little pin that sticks out of the crankshaft gear into the pully was sheared off, not once, but twice! Potentially, the pin sheared again, the signal plate is not properly measuring time, and the crankshaft sensor is throwing a hard fault, and triggering the misfire. That doesn't explain the low compression problem though.....

 

[nwoods]

on a related question, what years Montero Sport share the 3.5L SOHC engine with the Gen 2.5's?

 

[BOPOH]

i wouldnt worry too much about loss of compression. If i'm thinking this right - your engine is misreading timing and turning off first cylinder, cylinder walls and rings are not heated to proper size so compression is reading bad. It's like doing compression on a cold engine, day/night difference. Fix timing reading plate and then check compression again

 

[Salonika]

If timing reading plate was messed up wouldn't that screw up timing for all cylinders?

 

[BOPOH]

it probably did, but it also may be just a bad spark plug not firing or maybe somebody forgot to plug in some electrical connection(or not good enough) thus causing cylinder one to skip - told you should've checked it first

 

[IncorpoRatedX]

broken spark plug would be why the plug was fouled, it wasnt sparking, it couldnt.

50 psi, hmm. If that cylinder has been getting fuel pumped into it and not burning it off, check and likely change your oil since it will probably have fuel in it. might've boogered the timing a touch at some point and bent a valve, but also, could be a bad read, best to deal with it afterwards but it could mean a total tear down.

Major thing here is to not run the vehicle anymore. likely the crank trigger plate or the crank sensor is damaged from the pulley getting loose. I thought I mentioned this already in your first post? a hard fault usually means damage to the sensor. what i've seen is the plate getting some movement and just chopping the sensor to pieces.

WHILE YOU'RE IN THERE
maybe replace that hydraulic tensioner with an OEM unit?

 

[nwoods]

Weather was cooperative today. Finished the tear down of the front end. Man did I have a tough time with those two bolts behind the compressor holding on the mounting bracket. After about 2.5 hours, I got those two bolts out and the rest was easy.

Good news so far. Timing marks look great. Belt does not appear to have slipped at all, and the crank sensor and timing plate look okay. I know the crank sensor is reading as bad, but I was afraid it had be sliced up by a loose timing plate or something, but it all looks okay.

Passenger side engine bank:

Driver side engine bank:

Bottom end crank gear and sensor mount:

(ignore the second washer on the crank bolt, that's just there so I don't have to screw it in all the way)

Does anyone see anything obviously wrong? If so, I'm not seeing it. Please let me know!

 

[jaccox23]

Correct me if i'm mistaken but isn't there supposed to be a small stud on than crank sprocket? the one so that the harmonic balancer lines up and doesn't spin against the sprocket. I see what looks to be where it used to be in that final picture but it looks to have broken off and the crank and harmonic balancer were not spinning in rhythm but rather the crank was just grinding against the harmonic balancer under load. Maybe its the position of the crank in that pic and the little stud is on the bottom. Not that it will help your situation it was just an observation could possibly end up backing the crank bolt out later down the road if you don't have the little stud on the crank sprocket.

 

[nwoods]

Good eye! Actually, it's there in the photo, it just got driven in when I tightened the crank bolt to turn the engine to align the timing marks. I'm pretty sure I can drive it back out again when I remove the crank gear to replace the timing plate. If not, I'll source another one from the junk yard.

 

[skid]

i wouldnt worry too much about loss of compression. If i'm thinking this right - your engine is misreading timing and turning off first cylinder, cylinder walls and rings are not heated to proper size so compression is reading bad. It's like doing compression on a cold engine, day/night difference. Fix timing reading plate and then check compression again

I would worry the most about low compression. Engine will never run right and can cause other issues. Minimum 120 psi is what I like to see, but seen 200 on some engines cold. Leak down test to trace leak.

Sent from my SM-S978L using Tapatalk

 

[nwoods]

So its decision time. How much money do I pour into this thing? I am sckeptical that I have the right tools and ability to rebuild the engine. Consider that the only thing remotely like this I've ever done was a one cyclinder lawn mower in high school shop class 30 years ago.

I can replace the timing plate and crank sensor for under $50.

I can remove the intake manifold (I'm pretty confident I can do that), and replace the valve cover seals and gaskets. And I know I need to do the spark plugs and wires.

But that won't fix the low compression in cylinder one. Am I wasting my money investing in new parts if I can't fix the low pressure issue?

 

[nwoods]

Made more progress today. Successfully removed the intake manifold. Wow is there a lot of bolts to that process. Will be interesting to see if I can reinstall that thing correctly in a few weeks!

So I finally pulled the crank sensor and found something very odd. Check this out:

Then I pulled out the spark plugs to see what they might be saying. I wish I knew how to read spark plugs. Any interpreters here on Expo? Here's what I've got (bank 1 - cylinders 5, 3, 1, with 1 at bottom of image):

Spark Plug #1 is the one that has a small part of the porcelain broken off. It's very small, but it is missing, and presumably could have damaged one of my valves.

A leak down test will help me figure out where to go from there.

#3 and 5 look okay to me. Gap is about right, a bit chalky at the base of the anode, possibly sparking across to the base instead of to the tip?

Bank 2: Cylinders 6, 4, and 2 with 2 at the bottom:

Spark plugs 6 and 4 have ZERO gap. Plug number 4 is heavily fouled. Why? How did #6 and #4 loose their gap? I have no idea what's going on here. However, #2 looks pretty good to me.

If I wasn't having compression issues on #1, I'd say just replacing these spark plugs would solve my issues, but i don't think I'm going to get off quite that easy.

Next step, get a compression tester and check all cylinders, then do a leak down test on #1 and maybe #4

So that's what the valve covers look like!

 

[nwoods]

Bonus question. What should I do about cleaning stuff up? My valve covers are filthy, and the inside of the plenum...yikes! What do you recommend I clean this stuff with? Also, should I wipe down the intake inlets that leads into the cylinders? Or would crud fall into the cylinders and cause more harm than good? These things are filthy dirty. Check out this photo of the inlet at the bottom of the plenum:

 

[Salonika]

I'd just remove it and clean it, you've gone this far, why not? I believe the fuel rail is the only thing stopping you and I think you can just lift that up and out right along with the injectors. FYI if you do you'll need to replace the compression washers with new ones. I made the mistake of reassembling with the old ones and ended up right back in there about 3 months later with a coolant leak. They are marked as one time use only in the FSM.