[DrD]

That was a great post - thanks! Maybe what I'll do this weekend is pull the plenum and swap injectors between 4 and 5 and see if the misfire moves, and if so, swap out the injector. As you pointed out, it would be interesting to know how a misfire is detected by the engine - I can disconnect coil packs, the engine idle goes down, but it doesn't throw a code (pending or otherwise) reliably - maybe the detection algorithm only looks periodically, and it has to be disconnected when it's looking... who knows. The diagnostic tree starts having you check wiring harnesses after this, and looking things over, I don't see any damage. I did replace a coil pack plug a little while back, but that was on cylinder 5, and you don't really stress the cable when relocating pins from one connector to another...

How were you measuring the misfire - I have a different code reader (AutoXray EZ Scan 4000) - I have had to wait until the van acts up enough that it stores a pending trouble code.

 

[DrD]

I haven't checked the compression yet. I am going to go ahead and move the injector - I will check compression after that (I plan to do that in the morning, then I'll drive it a bit to warm it up, and check the compression). I have two sets of o-rings for when I move injectors (drove the van to/from the store for that and it worked just fine... no issues at all. I haven't been able to get the van to do it when I drive, just when my wife is driving it (it's her daily))

My scan tool is an older model (I can't even find AutoXray any more - I think they got bought by Actron, but there's no info on legacy product) - I have looked into Torque Pro, but it's not clear what it can/can not see (I have played with torque lite, but it's pretty limited). I was looking at the manual for my scanner, and while it does show various misfire things, that's in the extended software package which they only had for domestic makes, and now I couldn't even get that since they appear to be gone!)

 

[DrD]

Here's a thread going on right now where there is a compression issue and it's easy to spot with a trained ear during the crank:


http://www.odyclub.com/forums/9-pro...s/9-problems-concerns/310105-starting-issues-after-timing-belt-replacement.html

I will just use my compression gauge. everything sounds normal.

Sent from my SM-G900V using Tapatalk

 

[DrD]

Ok - pulled the intake plenum - interestingly, the intake runner to cylinder 4 was pristine, while the the others had the normal carbony sort of deposit on them.

Pulled the fuel rail and injectors for the front bank - there were a lot of deposits (brownish) on the ends of the injectors - particularly on the nozzle plate (not sure what it's called - the metal disk with the 8 tiny holes in it) - swapped injectors 4 and 6, then cleaned all three of them using intake cleaner and q-tips and a plastic spudger. Figured I should pull the other fuel rail and inspect that, and sure enough, they were all gunked up, too. Cleaned them the same way, replaced the o-rings, and reinstalled the rails. Showed the wife the deposits on the injectors when I pulled the second rail and explained that she needs to start paying attention to where she gets gas (and I am probably going to more religiously run injector cleaner through the van)

I was concerned that since I had adjusted the valves about 9k miles ago, that maybe I messed up cylinder 4, so I pulled the valve cover and remeasured - they were right where I left them. Buttoned everything back up, fired it up, and its running well - idle seems very smooth. Let it idle for a while with no incident.

So for now, my wife is out driving around so we'll see if it throws a code. I am wondering if maybe the injector is sticking and releasing fuel after it should, and the extra fuel is washing the intake runner... hopefully the fuel system cleaner will do its thing and free it up if that's the case.

One thing that sort of pissed me off - for pretty much all of the injector sockets, the locking tabs were embrittled and snapped right off. I safety wired (used an insulated solid core copper wire) to hold them each in place, since there is a lip on the end of the injector where I can have the wire go and not be right up against the leads... if I have to replace an injector, I might go ahead and replace all of the connectors (if I can find them).

for now we wait and see if it throws a code again. I didn't get a chance to check compression yet - maybe tomorrow (definitely tomorrow if it throws a code while the wife is out and about)

 

[DrD]

Interesting! It was a really stark difference in the plenum, and the difference looked pretty similar to yours for the lower part of the manifold, with the leg for cylinder 4 being quite a bit cleaner. It was really weird on the plenum - it was pristine with no deposits in cylinder 4! We drove it a bunch this afternoon, and it was a pretty hot day. I just drove it to fill it up with gas (ran through a bit under a half a tank with a big bottle of techron in it, so that is hopefully cleaning things up) - filled it up with 12 gallons and another big bottle of techron (the one that treats up to 20 gallons) - will run this one through and see how it goes.

On the injectors, the guck on the plastic parts wiped off for the most part (just a thin layer) with a rag no problem, but the stuff at the end was more persistent. There were a number of injectors where one or more of the holes in the pattern of 8 seemed completely obstructed - afterwards, checking with a magnifying loupe, all of the holes looked clear - hopefully it's not too gummed up inside the injectors.

The van is running noticeably smoother now - didn't give the rough idle or throw any codes. Crossing my fingers that this was it!

 

[DrD]

And it's back. Not sure what to try next. I went ahead and checked the harness to the coilpack on cylinder 4, and it seems fine - pin 1 shows battery voltage, pin 2 shows ground. No changes when I wiggle around the harness or the connector. Tried cleaning the contacts, but that didn't help either. The rotten thing ran flawlessly all day today - no sign of issue. Then this evening, the misfire is back. I am wondering if maybe one of the valves is sticking now and then or something like that... maybe one is really carboned up? my hope is that the fuel system cleaner will take care of that. After watching the vids above, I am thinking the chemtool stuff is the next thing to try. I am not sure if soaking in a container of the straight material is the way to evaluate them, but there is clearly a difference, and it's hard to imagine one of the others doing better after being diluted in gas...

ugh.

 

[DrD]

Did a compression test this morning (warmed the van up, pulled the fuel pump fuse, removed all the plugs, then went around, doing 5 cycles per cylinder - checked all 6 multiple times) - compression was nominally identical cylinder to cylinder (about a 4% difference between the highest and lowest)

All of the plugs appear identical - no deposits/ash/oil.

And of course, the van is running beautifully this morning... idle is smooth, no misfires, etc. I just don't get it.

I am leaning towards maybe the cylinders are carboned up, and for whatever reason, cylinder 4 is particularly bad... considering running a top end cleaner and seeing if that helps.

 

[DrD]

Do you think it's deposits on the cylinder itself that would be causing the issue? I was thinking maybe on the valves, but would I be able to see that with a consumer borescope (can they look upwards fairly well? I have seen one at harborfreight, but I am guessing it's sort of junk...)

 

[DrD]

Unfortunately, I don't have a leak down gauge set. I have not checked fuel pressure yet - will do so this week if I have a chance. Wouldn't be too surprised to see it low (van has a bunch of miles on it, and while I have changed the filter, I have not changed the pump or pressure regulator) - I was thinking if it were a low fuel pressure issue, I'd be seeing a random misfire, with more than just one cylinder impacted. Not much else to check, though. I checked and cleaned the three connectors to the PCM, but didn't see anything amiss with them (just cleaned them for good measure).

I was wondering if the PCM could be the problem, but wouldn't think that would be an intermittent issue.

 

[DrD]

Just to confirm, you swapped injectors 4 and 6? Are you continuing to receive misfire on cylinder 4?

That is correct

Are you getting multiple cylinder misfire code?

No - only cylinder 4 (P0304) - no other misfire codes

Another thing is the clean #4 intake runner.
I vaguely recall that fuel is a cleansing agent, so too much fuel will cleanup carbon build up.

That was what I was thinking. Maybe one of the intake valves is sticking a little, allowing the fuel mixture to be pushed back up into the intake runner.

The clean intake runner for cylinder #4 has been bothering me for the last couple of days too, but I can't put my finger on why it would be clean. The deposits are due to the PCV system putting the crankcase air back into the intake manifold. Fuel does wash carbon buildup but the deposits are prior to the injector, aren't they?

yes - the plenum is definitely further up! That's why I was thinking something like a sticking intake valve - being slow to close

The problem is very intermittent. When it does it, the idle is poor and the van shakes, accompanied by the flashing CEL, and a stored code. Most of the time, it's been running beautifully. My wife drove it around all day today, and it ran like a top - no issue at all. Which is making me think carbon fouling, that's being cleaned up by the fuel system cleaner...

Everything seems fine electrically, and mechanically, as far as I can test, is a-ok as well. The heavy deposits on the ends of the injectors makes me think that there could easily be similar deposits on the valves...

 

[DrD]

when it's doing it, it's very evident, but I can't make it misfire. It was misfiring on Thursday (mid morning when the wife called in a panic) then was fine Thursday when I got home from work. On Friday, it was mostly fine all day, but did have a code when I checked it in the afternoon. On Saturday, it was fine in the morning, I moved the injectors, and it was fine all day driving around, until late in the day then it did it a bit. Sunday it was smooth as glass - did the compression test, etc. and drove it a bit during the day without incident. Only thing I did to it last night was pull the three big plugs from the PCM and clean them thoroughly with electrical contact cleaner, as well as the plugs on the PCM itself, let them dry, then plugged them back in. My wife drove all around today without a problem, either.

The clean intake runner suggests fuel is getting up there, which makes me think a sticking valve, so hopefully the cleaners are taking care of it. I want to try something more aggressive on the top end - I have seen a bunch of things on using water, as well as some of the top end cleaners... not sure what I'll try.

 

[DrD]

Well - everything is running fine since the weekends festivities. Maybe there was something in one of the three plugs to the PCM - an intermittent contact or something like that - or it was a carboned up/sticking valve that's freed itself now with the injector cleaner... so far, two half tanks, each with a large container of techron have gone through the engine, and I just put in 10 gallons (on top of a little my wife put in yesterday) with a can of BG12... if it stays ok, maybe I'll run another tank with fuel system cleaner through it and call it good. The van is running perfectly now - idle is smooth and constant - seems to be ok...