Seems simple enough. I'll give it a shot.

 

Well, there's quite a few things that will induce the same exact failures. Now, to find the root cause, you've got to know a few simple things.

Misfires means, the cylinder is not firing or, that it's firing prematurely. Now, to map this out in your mind, you begin in the simplest of systems to the more complex systems as outlined below.

CAUSES OF MISFIRES

-Ignition wires low quality wires that are not wired to the TSB thus inducing induction cross-fire, ground out condition, voltage loss. Other: boot is not fully seated nor engaged at cap or plug or, poorly crimped contacts.

Poor Cap and Rotor cracks, bad pop rivet on rotor, arc / no arc condition

Spark Plugs wrong type / length

Faulty Dwell CKT at Hall Sensor throws timing off intermittently or does not work at all in some instances.

Intermittent / Faulty CPS will cause rough running / misfire condition

Faulty CKPS Intermittent CKPS. NOTE: will induce failures across all, not just one cylinder.

Bad Coil Usually shows up as OBD code 42 or 43 if my memory serves me correct but, sometimes it will not show up either thus induce misfire code instead.

Faulty Coil Driver CKT at the PCM coil CKT may be on all the time thus arcing inside the cap as the rotor goes around or, it may not be switching the ground in time.

-Fuel pump (which results in low output thus leading to a lean mix thus leading to a no-burn condition thus tripping an OBD code at the PCM level. Now, this also breaks down into more failure modes within this one system and they are listed as follows:

* clogged or restricted fuel filter
* low power at the pump
* bad Fuel Pump Relay at the PDC
* worn fuel pump motor

Faulty Injector

*clogged injector thus not allowing proper A/F ratio thus leaning out the mix thus misfiring.
* Jammed or sticking injector valve
* partial short or open coil
* clogged filter basket

Vacuum Leak: injector and intake level

* Dry rotted, lower O-ring. Allows excessive air thus leaning out the mix, thus misfire.
* Intake leak- usually caused by brake booster leak or, TB gasket leak or, IAC leak or, open PCV or, broken vac line/s and leaking tranny vac switch.
NOTE: this will usually induce misfires across all cylinders.

Map Sensor worn / out of range thus throwing the A/F ratio off. Affects all cylinders and is not isolated to one.

PCM Issues

* faulty coil driver CKT
* faulty injector driver CKT

Electrical / Wiring

* Fault in the wiring harness that supplies the injectors
* poor ground for injector ground
* poor ground for coil driver CKT

TOP END ISSUES

* sticking valve
* stuck open valve
* collapsed lifter
* cracked head- dry crack between valve seat and / or plug hole
* chipped valve
* weak valve spring. Insufficient force to keep valve closed thus, low compression.

Most of the time, it's usually the ignition wires that cause the problem nine out of ten times.

Start with the simplest thing first (ignition wires). Route your wires to the TSB first and then retest. http://dodgeram.info/tsb/1998/18-48-98/18-48-98-v8.htm

What brand of plugs are you using and which model? Some have longer than the OEM spec'd .750 length which puts them further into the combustion chamber.

CM

 

CM, thats an applicable and thurough reply but it dosent address the evidence from the picture to reduce the likely possabilities, it also jumps to conclusions that the issue is spark related, where a missing electrode is usually fuel related.

The electrode is missing, most likely, from extended detonation. This is caused by high CYL temps, caused by a lean condition. If his porcelin looked like my toilet I'd be all over the injector, but its kind of brown so no smoking gun.

I think a leak down test and ohm'ing or swapping the injectors is the best first step because its free. Your dead on with routing the wires correctly, and I would go further to spray them down with a water bottle, and look/listen for arcing. If your brave you can use your hand to feel for it.

 

I would say your #7 cylinder is running extremely hot. Seems like a lean condition. Swap injectors and see what happens. You may have gotten some crap in the injectors or fuel rail when you were doing the plenum job. Also make sure the injector is seated properly, and has a good electrical connection.

 

^^^ ya move it to cycl 1 or sumthing and see if it will miss and throw and code on 1

 

Well how bout a curve ball. CSX I think you may have been on to something with the crud in the injector. Last night I went home and took the fuel rail off and swapped injectors 7 and 5. Looked like the #7 wasn't really squirting at all. Didn't see any fuel residue or anything like that on it when I pulled it out. But swapped it anyway. Turned the key after I got it all back together to check for leaks. Low and behold I got a different code. TPS sensor bad. So went up and got a new one. Found that the one that was on the truck was cracked and had possibly gotten water in it. Changed the TPS and idled normal. Let it idle for 10 min no miss. Drove around town to warm it up let it idle. No miss. Drove on the highway for about 5 to 10 minutes. No miss. SO how is the TPS linked to the miss???? No idea how but it seemed to help. Throttle response went way up. Idle down is normal. Can anyone hit this curve ball?? I'm gonna drive it today and see what happends. If it comes back I'll report back. If not I'll see if it comes back at all. Maybe just taking the injectors out and moving them around cleared the gunk or whatever in the rail and the injector.


BTW CM I am running the champion copper core plugs. Don't remember the number. But its the same as the factory plug. Also I was talking to one of the guys at the parts store and he was saying it was possible that the injector was stuck open causing the plug to look like that. Dunno if that's true but thought I would throw it out there for validation.

 

I merely listed out all the possibilities for a missing condition starting with the simplest of components to the more complex system level failures. I did not jump to conclusions and in no way ever stated that it was spark related.

I started off by telling him how to troubleshoot as he had asked where to begin by starting off with the simplest of system components working his way outward. You can not just look at the injector only. You must also check the harness relating to that cylinder plus, you've got to check vacuum and compression on the cyl as well because, in all cases, if one of those is out of spec, it will induce a lean condition thus causing the same end result.

I would also never use your hand to feel for an electrical arc -EVER and, what your suggesting is going to shock end user with 20KV thus possibly killing him. NEVER touch the ignition wires to feel for arcing. Simply reroute the wires per the TSB and retest.


CM

 

Everything in the system is related and, the TPS feeds back voltage to the PCM. From there, the PCM adjusts the fuel rate and EFI timing in correlation to the TPS voltage.

Everything works together as a system. This is why I mentioned the part about sensors- MAP sensor in particular. Usually, when the TPS goes south, the idle oscillates (just like a bad IAC valve will induce) and, when driving, it lurches, speeds up, slows down. In my experience, I don't think it's your TPS. If it was, it would affect ALL the cylinders- not just no 7.

So, we look at what changed (that was a change of removing one fuel rail and swapping the No 5 and No 7 injectors and adding a new plug and finally, a PCM reset), what probably happened was you fixed a vacuum leak on the No 7 Cylinder that you didn't know you had.

I can't see a TPS fault inducing misfire on ONE cylinder- it's not possible. And, I think when you were removing the rails and injector, possibly, it was damaged during that time period otherwise, you would have seen that OBD code for that earlier. I don't think it was the root cause for your failure nor do I think it's a clogged injector as if it was- that problem would have tripped a code for the No 5 Cylinder instead. I think what you've got going on is that your chasing things around vs. finding out for sure what the root cause is.

If it's isolated to just one cylinder only, you can really target on that one cylinder and everything associated with that one cylinder. I would also check your filter baskets on your injectors. Did you look at the filter baskets when you removed them? Reason being: the rails have a tendency to rust on the inside thus flaking off and ending up in the filter basket thus restricting fuel flow and, when removing them, they either fall out or move around just enough to allow fuel to pass a while before clogging again. The root cause in my case was bad rails and, no matter how many times I replaced and / or cleaned the injectors, I kept getting the same code.

Now, another possible reason that it's now fine is due to a PCM reset. Each Injector is on it's own CKT and is controlled via the injector driver CKT at the PCM level. If this happens again, simply reset the PCM. If the problem goes away, it's PCM related thus requiring you to check the ground path on the faulting injector CKT and, if that tests fine- your PCM is malfunctioning.

I would test your truck out under full load going uphills under full operating temps. Now, FYI- the computer (when reset) will NOT throw any codes even if there's a misfire condition. I know this system inside out all the way down to the PCM level and, it's programmed by default to allow misfires over a certain time period. Only when the misfires exceed the maximum allowable within a set time frame will it trip / throw a code. Sometimes, it will occur after one to three KEY ON events. I have had this happen as well. Resetting the PCM made everything seem fine until, days later and, it threw the same code. It was running me in circles. I finally decided to inspect and test everything out in a systematic method that I would apply in my field of work. That's when I finally found the root cause was bad fuel rails clogging the injectors. I made a new set- problem solved.

Another intermittent problem is valve seating. During operation, the valve will sometimes seat fine while sometimes it will not thus not holding compression thus causing intermittent misfire / rough idle condition. It can go for a long time without failure to, being very annoying due to not seating for a while as well.

A cracked head will also intermittently cause the same exact failure and, depending on the environmental temperatures, it may close or open up thus running fine sometimes and sometimes not.

All of those are isolated to one cylinder specifically- usually. SOmetimes, depending on where the crack is (between two cyls) it can affect two clys vs. being isolated to just one.

One last thing: Champion plugs are THE worst plugs to use in my opinion. I never had any luck with them at all. Let me just tell you that a mechanic friend of mine had to go through boxes of Champion plugs just to make a set of eight that worked. He had the vehicle on the scope and could see how the plug was firing. They were all over the place. I would immediately change to NGK Vs. Do not use Platinum plated ones though. One other standard plug to use would be Autolite 3924s. I may have inverted the number there but, in any case, I highly discourage the use of Champion plugs.


CM

 

Give it a few days and see if the problem returns. If I recall correctly, the problem abated some the last time you changed plugs as well?? and then came back?

It could be any number of things if the problem is indeed gone. The vacuum leak as suggested by cmckenna, or, maybe the injector connector was just not making good contact, and shuffling them around changed that.

I agree that the TPS wouldn't cause a misfire on just one cylinder.

 

Right I agree that the TPS wasn't the problem. CM thanks for all the info. You're a wealth of info around. I thank ya for that. I am probably just chasing the problems. But for now its working. So maybe it was a vaccum leak that I didn't know about. I know that usually after i reset the pcm the code came back about 5 min later after idling or givin it he!!. But now idling and giving it hell have no issues. So I don't know. Oh yea I also know not to touch the ignition wire with my bare hands. Had that prank pulled on me too many times as a kind. Dad was working on the mower hey hold this wire while i pull on the string. ok AHHHHHH That thing shocked me and the Laughed. Know that trick not gonna do that again. Especially with 20kv forget that. Good idea but no.

Thanks for the help guys. I really appreciate it. I'll report back in a couple days or if the code comes back. Hopefully I can add this problem to the score. DF 5 truck 1