Trouble shooting a misfire on Cylinder #1

[nwoods]

I finally got my Monty back together again after 5 months of being in pieces in my driveway. 1998 Gen 2.5 with the 3.5L SOHC engine.
The good news is that it runs! The bad news is that it runs poorly, and is missing Cylinder #1.

Not being a mechanic, I really don't know how to trouble shoot this. I pulled off the spark plug wire at the ignition solenoid and saw sparks (and got a nice little zap in doing so), so I don't think its the ignition system. Also, when I pulled of the plug wire, there was no change in the way the engine ran. The spark plugs are new and properly gapped. Is there a way to see if the wire is bad?

Other potential factors are that the pressure in Cylinder 1 is low. Target values per the Manual is 170 PSI or thereabouts, and I got 30 psi dry, and about 130 psi with a spoonful of oil poured in. The truck does not smoke when running, but it is clearly running on 5 of the 6 cylinders. My previous problems of timing seem to have gone away with the installation of the correct model year timing plate (about 15 degrees different!) and new crank sensors, etc...

If I can get cylinder 1 to fire, it would be awesome. If my rings are shot, I can live with a bit of oil consumption and tailpipe smoke

Thoughts, suggestions? Sympathy's?

 

[jeep-N-montero]

Are the wires new NGK?

 

[Toasty]

Injector plugged in? and operational?

 

[nwoods]

Are the wires new NGK?

No, I reused the wires that were on it. They are OEM, but I have no idea if they are original. I bought the truck with 180k miles, now at 205k. Is there a way to test if the wires are bad? I suppose I could swap wires with #5 or whatever, but that's a PIA due to the need to remove the intake and all that.

 

[nwoods]

Injector plugged in? and operational?

Pretty sure plugged in, no idea if operational. How to test?

 

[normal_dave]

I guess I should read through all of your older posts to get up to speed, but let's start with what you have in front of you.

Do you know it is cylinder #1 due to pulling the check engine light code?

If so, then just swap the two paired wires at the coil pack, # 1 to # 4 and #4 to #1, clear codes, then test again to see if the failed cylinder code suddenly appears on #4. If that is the case, then you simply have a bad wire. Our coil packs fire two cylinders at the same time, one is on the exhaust stroke and of course is wasted, when that cylinder comes back to the compression stroke, of course it fires compressed fuel/air, and the other cylinder fire is wasted on the exhaust stroke.

You could also swap one coil pack for the adjacent, leaving the wires in their original place and see if the problem moves to another pair of cylinders. I think you should also be able to resistance test your plug wires with a digital test meter set to around 25,000 ohms. They should read somewhere around 25K ohms, but you would have to pull the spark plug end of the wire to test. black lead to one end of the wire, red lead inside the spark plug end of the wire. btw, too low a range setting on the meter won't read at all.

Here's an image of our cylinder numbering and firing order. If you confirm the problem to the #1 cylinder, can you possibly fish the spark plug wire out of the tube without removing the intake on the #1 cylinder?

While you're at it, physically trace every wire back to the coil pack using the above diagram. Won't say how many times I've messed it up (forest vs. trees issue).

Last, I'm a little concerned about the low pressure on the compression test. 30 psi in any condition leaves a lot to be desired.

Good Luck, you've certainly done quite a bit of mechanic work so far, might as well keep going.

 

[nwoods]

Thanks Dave. Yes, borrowed OBDII reader gave us P0301 after about 20 miles of driving after the reassembly.

Yes, I can access Cylinder 1 with everything in place. I'll try the #1 to #4 wire swap tommorow. It's possible I have a bent valve in that cylinder. A small piece of the old spark plug ceramic cone was broken off at some point. It got out somehow

I'll post a video tommorow of it running. The audio is clearly missing one cylinder in operation, but I don't know if valves would cause that or what it would sound like if it was.

As for the wire tracing, yes, I screwed that up the first time two. I thought I was smart and labeled the wires before removing them, but somehow mislabeled 3 and 5 and after reassembling the intake i realized the problem. Fortunately I was able to tease out the spark plug tower connectors by removing the throttle body and loosening (but not removing) the intake assembly, and fixed the wire order before ever starting up the truck.

 

[Pntyrmvr]

Not being a mechanic, I really don't know how to trouble shoot this. ...pressure in Cylinder 1 is low. Target values per the Manual is 170 PSI or thereabouts, and I got 30 psi dry, and about 130 psi with a spoonful of oil poured in.

Sympathy's?

Rings are done. Valve issue wouldn't change cylinder pressure with spoonful of oil added.

Leak down test will prove it. You'll hear air at the oil filler.

"Talk is cheap. Whiskey costs money."

 

[jeep-N-montero]

Why would you go through all of that work and not replace the wires while you had it apart?

 

['round n' back again]

Never mind my bull **** here Normal Dave nailed it.




go ahead and swap wires around. if the miss follows the wire that was on cyl.1 then you really need a new wire. or somewhere along that wire there is a short to ground. check your boots carefully. (spark plug boots not your shoes)
this is definitive check to isolate that wire as the problem child. if the miss is still in cylinder one, suspect your coil. work your way back through the ignition voltage to its source. a simple problem.
its not necessary and is often a waste of money to replace good wires. don't do that unless you know with certainty the wires are shot. a simple ohm test will tell you that.
inspect them carefully . there are a lot of tutorials online im sure that will tell you what to look for in a bad wire.


your compression is a lot less simple though the culprit is far more obvious. research online for any clever fixes. my only clever fix is a tear down re ring and a hone/bore if necessary.


BUT: be sure you did your compression test properly. a person i know quite well once performed the above suggestion only to find that his problem lie not in the rings but in the insertion of the tester incorrectly (ok,ok so i was a kid in them days when i did that.)

 

[nwoods]

Rings are done. Valve issue wouldn't change cylinder pressure with spoonful of oil added.

Yeah, I agree, but would that cause the misfire?

 

[nwoods]

Why would you go through all of that work and not replace the wires while you had it apart?

It was yet another $100 potentially thrown away if it didn't solve a problem. This cheap car is bleeding me dry. My Land Rover was far less expensive to own than this Monty.

 

[normal_dave]

I can't speak from direct experience on the Rover, only reputation, but I can attest to the worthiness of the Mitsubishi, once you get ahead of the maintenance curve.

I believe the majority of our Montero's have just had basic maintenance done to them, from owners who may not have ever used them as they were intended to be used, or taken the extra steps to take care of those nagging Mitsubishi gremlins.

On both of my trucks, it would have been easy to curse the Mitsubishi engineering department and walk away in frustration. After sticking it out, I've determined that the reliability and design issues aren't worse than any other make, and as I get older, have about decided that when properly cared for, are better than most makes, certainly the most capability for the dollar of anything I've experienced, along with a decent level of luxury (Limited models) found in makes costing 3 times as much.

Monteros seem to be worshiped in other parts of the world, I just don't think they ever caught on here. This also generates a lack of knowledge and skills in the repair market. By the time we get a hold of one, well there is a large hill to climb in terms of catching up items that should have been done all along. Some of us have been lucky to find the rare meticulously serviced trucks, not me. For example, our engine blocks have a high nickel content, making them serviceable and strong for a long time, provided the other maintenance doesn't fall down.

You are the only one to decide when to throw in the towel, but I recall you said you really liked the truck, and got it at the low end of the cost spectrum. So look at your overall expense vs. capability situation and make a decision. Just know that I think you can in short order and with reasonable cost (but lots of labor) get "ahead of the curve" and enjoy the truck once you take care of what the previous owner neglected. If not, then cut this one loose, take your money and experience and apply it to a more worthwhile Montero candidate that hasn't been neglected as much.

Sometimes better the evil you already know...?

Good Luck whatever path.

 

[nwoods]

Good news, the wire for #1 spark plug was bad. New wires on the way. I have a loaner installed at the moment from 145,000 mile Monty that is being rebuilt. Engine definitely runs much smoother on all 6 cylinders Now you can really hear the cracked exhaust manifold on the passenger side. Sigh.....

 

[normal_dave]

Great news, troubleshooting for the win!

If you are going to do the plug wires, I know we've all been there before, but I found this step by step from DougC to be so handy, that I use it every time. I was making the job harder than it needed to be. Also, it's written for a Sport, so skip the step or two that doesn't apply to our Monteros. Wish I could make it a "sticky" note here.

http://www.justanswer.com/mitsubishi/4t9po-mitsubishi-montero-sport-change-spark-plugs-2003.html

I'm guessing things look a little better today.