Cylinder 4 misfires at all ranges

[craigwatanabe]

Okay I never got a response in another thread so I'm reposting my dillema here:

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Hi I'm new to this forum and have been addressing this problem with my 2000 MPV Minivan with the 3.5L V6.

I went to Checkers and they plugged in their scanner. I can't remember the code but they indicated cylinder 4 wasn't firing. Incidently there was a clicking sound coming from the area around the coil pack. The misfire occurs at all RPM's with an occasional backfire when accelerating from a stop. I'm concerned the backfiring will take out my Catalytic converter's elements so I haven't been driving this car unless I have to.

Suspecting an ignition problem I removed the number 4 spark plug wire and got spark. There was no difference in the engine sound (same misfire sound) so I suspected a bad spark plug. Ironically when I removed the spark plug wire (plug side or coil pack side) the clicking sound went away, coming back when I reconnected the plug wire.

I went ahead and replaced the plugs, wire set and coil pack with no change.

Fuel mileage wise I went from just around 300-miles per tank to less than 150-miles per tank running 89-octane gas when the misfiring happened.

I considered the O2-sensor but figured if that was bad the engine would cold idle okay and get worse as the engine heated up (I'm in Hawaii so no severe winters, never dropping below 67-degrees).

I'm thinking possibly the fuel injector for that cylinder but then the fuel economy wouldn't go down drastically over one injector not opening right?

I'm at a loss right now but somehow cylinder-4 seems to be involved as it's the only cylinder that has no difference in engine sound when I remove any of the spark plug wires.

When I checked the engine bay at night under total darkness, I was seeing spark tracings running along the #4,5 and 6 plug wires. I replaced all the wires when I saw this. A new set of wires resolved that issue but didn't cure the misfiring. I checked the secondary ground strap that bolts onto the coil pack and was getting continuity from the bolted strap to the engine to the firewall so I'm getting good grounding. The RF filter that bolts onto the other side of the coil pack also is okay and properly connected.

At this point I'm stumped and cannot figure out what's going on. Please anyone, is there something I'm missing or can correct? I'm not that mechanically inclined to test or remove the fuel injectors.

 

[jamesk]

ok first of all, around here a checkers is a fast food place. is it also a auto shop? i didnt know that.

second, theres 2 things to make a cylinder fire. spark and fuel. the first thing i would of check is the spark plug and coil pack and make sure that it is working properly. if that is working properly, check the fuel pressure in the fuel rail, make sure the fuel pressure is good and nothing is clogging the lines. also check the fuel injector in that cylinder. that seems like the problem since only one cylinder is not working. but a fuel problem is just as bad a spark problem. both is needed inorder for a combustion to work.

let us know when you check the fuel injectors out. good possibiliity the one gave out.

 

[craigwatanabe]

I kinda figured it would be a defective fuel injector, however like I indicated in my initial post, I don't know how to get to that particular fuel injector. Both the injector and the fuel rail is buried under the intake manifold and at that point is beyond my abilities.

The curious part is that the ticking sound (which was coming from near the coil pack) went away as soon as I removed the spark plug wire from either side while the engine was running. The ticking sound reminded me of a spark jumping a gap however at night there is no apparent sparking going on that I can see and that's in total darkness.

I've read in other threads that resetting the ECU may be in order by removing the battery connections in order for the ECU to recognize the coil pack and or spark plugs. I haven't tried that but am willing at this point before submitting to bringing my car into a mechanic who can probably fix this thing in a heartbeat and a hefty price.(shrug)

 

[jamesk]

well you have to determine if that cylinder is getting spark or not. try switching around spark plug wires and make sure the coil pack and spark plug wire and the spark plug itself is good. im not familar with the mpv, does it have indivdual coil packs or wires going into one?

 

[craigwatanabe]

I did indicate in my initial post that I'm getting spark and that it did use a coil pack. A coil pack is one module with individual coils for each cylinder, hence it is called a coil pack. A typical ignition system consists of a single coil, coil wire, distributor, spark plug wires, and spark plugs. The 2000 MPV utilizes a coil pack where there is no distributor, instead the ECU sends the timing signal to the coil pack where it fires off each individual coil to the corresponding cylinder.

The coil pack is receiving the timing signal, and is sending spark to the spark plug. The spark plug is energizing and producing spark. I mentioned all of this in the initial post.

I'm starting to believe it's a defective fuel injector. As such, if it is a stuck injector, that pretty much would indicate no gas getting into the chamber causing the engine to stumble. But my concern is from a friend of mine who told me that driving my van can result in the elements in the catalytic converter to get damaged because of unburned fuel detonating in the cat's chamber.

Now correct me if I'm wrong, but if the fuel injector is stuck and not pushing fuel into the #4 cylinder, when the exhaust valve opens and flushes out basically nothing, there shouldn't be any unburned fuel entering the catalytic converter because the fuel injector never injected any fuel to begin with right?

I can see if the injector worked and the spark plug not energizing, then there would be unburned fuel exiting the exhaust valve thus detonating in the cat, but in this case the spark plug is working so if there were fuel coming from the injector, I wouldn't be posting my problem at all right?

I'm really beginning to believe it's a stuck fuel injector.

 

[techspeak]

If you hear the clicking, then your spark could be shorting out along the sides of the spark plug well. Stuck injectors don't click, (as the solenoid is stuck) and injectors dont usually sieze unless stored dry for long periods of time. Stuck injectors can also be freed by putting a rachet extension against it and tapping it with a hammer. Try a new wire on that cylinder, check the old one for holes along the plastic extender tube, usually if spark leaks from it, then it burns a tiny hole.

Have you checked if the spark plug on Cyl4 is wet from fuel?

 

[jamesk]

the fuel injector could be stuck open and just drain fuel into the cylinder causing it to flood. then unburn fuel could reach the cat.

 

[craigwatanabe]

A stuck open injector...that could very well be the problem and could be the reason for the excessive MPG loss, averaging about 150-miles per tankful.

So with a stuck open fuel injector sending unburned fuel down thru the hot catalytic converter, the possibility that this post detonation of unburned fuel can cause damage to the cat's elements is very possible then right?

As for the ticking sound. I've replaced all the wires with new ones and have checked them at night in total darkness to check for any arcing. I've replaced the spark plugs as well and as I've indicated before the ticking sound goes away when I pull the #4 plug wire from the plug side or the coil pack side. It's the exact ticking sound you'd hear when you try to jump the gap from a spark plug wire to the engine and get that arcing sound.

You'd think with a sound that loud you'd see a noticable spark, but there's absolutely no visual indication of arcing. I checked the old coil pack, spark plug wires and plugs to check for tell tale carbon marks from any arcing and they're all clean. This is just blowing my mind.

 

[techspeak]

As for the ticking sound. I've replaced all the wires with new ones and have checked them at night in total darkness to check for any arcing. I've replaced the spark plugs as well and as I've indicated before the ticking sound goes away when I pull the #4 plug wire from the plug side or the coil pack side. It's the exact ticking sound you'd hear when you try to jump the gap from a spark plug wire to the engine and get that arcing sound.

You'd think with a sound that loud you'd see a noticable spark, but there's absolutely no visual indication of arcing.

Well thats got to be your problem! Just a note, you wouldnt be able to see an arcing spark sometimes, esp. a spark that was arcing off down in the spark plug well, which could be whats happening. Obviously there is an issue with spark that needs to be rechecked. The sparking noise and it going away when you unplug the spark plug wire is so telltale. How do the plugs look? could the insulator be cracked? When your friend mentioned the catalyst, he was right in that any unburned fuel (from a non-firng cylinder, not necessarily a fully stuck open injector, which is really unlikely) would have to burn off in the cat, which can cause excessive heat and melting.

 

[craigwatanabe]

I've replaced all wires including the plugs. The ticking sound is coming from somewhere around the coil pack.

The engine is transverse mounted. If you're standing in front of the van looking in at the engine compartment, the number four cylinder is the front left spark plug location.

The coil pack is mounted near the fire wall where cylinders 1,2 and 3 are located on the intake manifold. The ticking is coming from that part of the engine, near the coil pack. The number four cylinder is nowhere near the ticking sound.

Regarding the condition of the old plugs, they looked normal, including the number four sparkplug. No carbon, slightly greyish white, not wet.

Not wet. Yesterday after running the engine for about a minute and revving it up to 2000 RPM for a short burst, I shut it down and remove the #4 plug. It's hot and very dry just like the other plugs.

If it were a stuck open injector, would the plug still be wet? And no, there wasn't any smell of raw gas when I pulled the plug from the well.

So if the van is running on five cylinders instead of six with fuel starvation on cylinder 4, could that be enough to garner a 50% reduction in mileage (150 MPG instead of roughly 300 MPG) and can I then rule out any possible damage to the catalytic converter since at that point no unburned fuel should be entering it?

Then there's that ticking sound again coming from nowhere near the culprit cylinder.

Once again all spark plugs have been replaced, all plug wires have been replaced and the coil pack has been replaced. Pulling each plug wire out one at a time while the engine was running (and idling rough), resulted in a noticable drop in engine performance. The only exception was of course #4 where pulling the plug wire made no difference in engine performance other than quieting the ticking sound. #4 plug looks just like the other plugs (condition wise) with no carbon build up, and not wet with no scent of raw gas from the #4 cylinder (with that plug removed)

Right now I'm thinking stuck closed #4 cylinder fuel injector...but what about the ticking sound? And that it goes away when you pull the #4 spark plug wire? I can pull it from the coil pack side and it goes away. I can pull it from the plug side and it goes away. It's as if the #4 cylinder is loading down the coil pack somehow. Can a defective or stuck fuel injector do that?

As I've indicated in my initial post, Checkers (Checker Auto Parts) hooked up their scanner and found that cylinder 4 was misfiring. I can't remember the code but at that time the code did indicate that issue.

That's about as much info I've gathered from post #1.

 

[craigwatanabe]

Update!!!

Okay I think the problem is back with the coil/spark.

I found out where the ticking sound is coming from. A spark is jumping from the coil pack to the spark plug boot. Occasionally the spark will find it's way to the spark plug (hence spark plug isn't wet with gas). But the ticking is from that contact point between the coilpack mount and the plug wire boot.

I've checked and made sure the boot is snug and all the way down onto the coil pack post and onto the spark plug itself. I even replaced the #4 plug wire with a known good wire (#6 wire from the old set).

With the plug wire pulled from the installed spark plug I stuck another spark plug onto the #4 plug wire and started the engine.

While grounding the threaded portion of the spark plug to a grounded section of the engine with the plug wire attached to both that spark plug and the coil pack there was no spark jumping the gap on the spark plug.

Turned off the engine, pulled the plug from the plug wire, started the engine up again and was able to get a spark to jump from the plug wire boot to the engine.

So I'm getting spark down the plug wire but nothing at the spark plug. Replaced the spark plug and grounded the threaded portion of it and no spark. Is it possible I have two defective spark plugs coincidentally at the same cylinder? Tomorrow I'll try switching around the #5 and #4 spark plugs and see if I can get cylinder 4 up and running.

 

[craigwatanabe]

Switched out #4 and #5 spark plugs and problem persists. I'm totally dumbfounded.

 

[techspeak]

replcement coil pack also bad? remember, it IS an american coil pack.

 

[craigwatanabe]

I was thinking the same thing but what are the odds of two coil packs going bad on the same cylinder?

 

[jamesk]

hows your electrical system in the car? any lights going dim or anything like that at all? maybe u shorted out the coil packs. i have seem that happen before.

 

[craigwatanabe]

Nothing out of the ordinary with the electrical system.

Well it's Christmas Eve here in Hawaii and I'll think I'll take a break from this car until the weekend, time to enjoy the egg nog.

Have a great Christmas everyone, see ya on the backside!

 

[Rawdawg]

Double check coil ground to firewall

Do all the coils share the same ground strap? or do they all have separate ones..if they are spliced together at some point , that may be where the arcing is coming from.........or clean the firewall and connector and reattach.
Im not familiar at all with the config of this motor, but thought it may be sumthin for thought.. hope u get it fingered soon.. good luck

 

[craigwatanabe]

There is a single ground-strap point for the entire coil pack and is located on the front right mounting point.

As for the location of the arcing, it is definately coming from where the #4 plugwire mates with the coil pack. That connection is tight. I even replaced the plug wire with a known good one and same thing.

One would conclude the coil pack is defective but the original coil pack and the new replacement pack is arcing at the exact same location. Coincidence maybe but unlikely. The cost to find out would be another $150 for another coil pack. If that doesn't work I'll have three functioning coil packs since you can't return electrical parts at most auto stores.

 

[craigwatanabe]

I finally got my van scanned with a comprehensive scanner that gave me a printout of what the engine was doing when it was happening.

The result: Defective Crank Position Sensor.

Makes sense, the replacement sensor is in the mail and I should be able to tell all of you if this is in fact the reason for the misfire.

Thanks for all the help, I'll keep everyone posted here to see if this will fix my problem.

 

[craigwatanabe]

So the Crank Position Sensor didn't do the trick, darn.

I'm just about ready to just go ahead and change the O2 Sensor. I'm told it shouldn't be the problem since the misfire is happening during a cold as well as a warmed up engine and the O2 sensor should only cause the misfiring at warmer engine temps.

Now when the engine does warm up, the misfiring does get worse to the point of excessive backfiring.