[Jatka]

Recently bought an 02 Grand Caravan that stutters hard under 2k rpms at about 45-55mph on acceleration. If I turn O/D off, it doesn’t do it because it doesn’t reach top gear, or if I give it enough gas that it downshifts, it’s fine. It has a slight miss at idle, only gets about an avg of 19/20mpg on the freeway, 13-15 in town. The stutter feels like when you hit the rumble strip on the freeway, but HARD.

Changed the spark plugs which were horrible with no improvement and changed the oil because I know that needed done. Not sure where else to start looking, beyond firing the parts cannon at it, which I really don’t have the funds or patience for. Done some research and nobody seems to have had quite the same problem.
Additionally, the CEL is on for a cyl 2 misfire, which I don’t believe changing plugs fixed, as well as an EVap leak. Plug Wires seemed to be intact.

Any help appreciated, I can give more info if needed. Praying it isn’t the tranny, the fluid is at the appropriate level and still has good color. SLIGHT black particulates if anything. TIA.

 

[BobNewhart]

If it were me, I would try to find a way to rule out the coil packs. Rule out the misfire. If it's not the misfire, then I'd start looking at the transmission.

 

[marvinstockman]

On a dark and rainy night, and with engine running, open hood and spray away with a water mist. Bad wires will show themselves.

 

[atoman]

No need for parts cannon, rule this out first:

Melted injector wiring harness 2003 Town and Country

Finally! I found it! I had codes p0300, p0302, p0304, p0172 and many others. I changed so many parts. the wiring harness was melted together, just under and behind the power steering reservoir. I taped it all up with a mile of electrical tape and gave it a lot of heat protection wrapping...

www.chryslerminivan.net

 

[Jatka]

Figured out my issue🙃
I have a cracked head or a blown head gasket. Thinking the former rather than latter. It was so small, They were able to hide it on the test drive, and keep me guessing for 3 months of driving it about 2k miles.
This first 90 degree day we had, I took it on a 100 mile trip and it said Peace ✌ about 3/4 the way through, gave me 3 hard kicks in the gas pedal and started running even more rough than usual.

Turns out, cyl 2 must have had a pinhole leak somewhere that was letting gas out and coolant in, but not enough to overheat it, to let white smoke out the exhaust, to use almost any coolant, or to mix any with the oil. So without a compression or head gasket tester, I wouldn’t have even known until it blew like it did.

This was causing my misfire, it was either mixing enough coolant or sucking enough unmetered air into the combustion chamber that it couldn’t ignite the Air fuel mix under 2k rpm, which is when I assume the piston built up enough friction and heat to ignite it and just barely fire(cringe). Cyl 2 now has no compression, the plug is sparkly steam cleaned, the cyl has NO carbon, and I can see AROUND the piston from the SPH, but it limped me home safe the last 20 miles, so thanks Chrysler for the smooth, reliable engine.
Amazed she lasted as long as she did with the PO’s serious neglect and surprised how far I was able to drive it with that cylinder being dragged by the others and mostly only running on 5. You wee

 

[Jatka]

Cyl 2 plug on the left, 4&6 beside it.

 

[atoman]

cyl 2 must have had a pinhole leak somewhere that was letting gas out and coolant in, but not enough to overheat it, to let white smoke out the exhaust, to use almost any coolant, or to mix any with the oil.
Cyl 2 now has no compression

Unless you see mixing oil and coolant or excessive white smoke, I wouldn't jump to conclusion of head gasket or crack... (valve issue seems more likely) PCM shuts down any cylinder it detects continuous misfire on, so clean plug and lack of carbon (on relatively new plug) may not mean much. Coolant leaking in the cyl would leave residue unless only water was in the rad.

Also, did you check compression on other cylinders?

PS: are those Champion OE spec plugs?

 

[Road Ripper]

I'm guessing head gasket. Well, unless there's a coolant port next to cylinder 2 intake port on the head (lower intake manifold gasket leak). You can leak just enough coolant to kill the cylinder sometimes, and the level drops so slowly you barely notice it. I had a Datsun 620 Pickup in college that did this, until one day while driving to school it started a HARD misfire. When I finally took the head off, there was a pie chunk of exhaust valve missing from the first cylinder = NO compression. That first plug was steam-cleaned when I pulled it out trying to diagnose a light miss during cruise, and I had to top up the radiator just a little bit now and then. Hey, I was learning (I was in vo-tech for auto mechanics). Nowadays I'm like "why didn't I see the warning signs long ago?". There was hardly any steam from the exhaust either.

 

[marvinstockman]

What is the tach doing when the van is stuttering/shuddering?

 

[Valhallalla]

PCM shuts down any cylinder it detects continuous misfire on

The PCM does NOT shut down misfiring cylinders. I have seen others post similar statements here before. I don't know where this bit of misinformation originates but it is simply not true. The PCM will limit engine RPM in the event of serious misfire in an attempt to minimize catalytic converter damage but it does not shut down individual misfiring cylinders.

I do agree to not jump to conclusions here and that further evaluation should be undertaken. If a cylinder has a large enough compression leak into the cooling system that there is no compression at all there would be significant over-pressure of the cooling system. It would be more pressure than the 15 psi or so of the radiator pressure cap. In other words there would be more issues than just low compression and cylinder misfire.

If a compression issue is suspected I would perform a compression test on all cylinders. Depending upon the compression results a cylinder leak down test would help determine where the compression loss (if any) is going.

 

[atoman]

The PCM does NOT shut down misfiring cylinders.

And this bit of knowledge is a fist hand experience? please enlighten us fools who have seen it behave otherwise.

Note: Most Chrysler PCMs will disable a fuel injector for a hard single-cylinder misfire. So it is common to have 1 or more injector drivers that will not cycle.

 

[marvinstockman]

Valhal, cylinders are shut down to prevent the cat from destroying itself from unburned gasoline.

 

[Valhallalla]

And this bit of knowledge is a fist hand experience? please enlighten us fools who have seen it behave otherwise.

Chrysler Engine Performance - Cylinder Contribution: Misfire Monitoring

Fuel-Based Misfire Diagnostic Tips Low fuel pressure and fuel contamination can cause misfiring with no codes, but may also cause a P0171 and/or P0174. However, the following less common faults can also cause misfiring without any helpful codes: Injector Faults Injectors electrically short or burn o

www.linkedin.com

First hand experience and the fact that I have never heard of such a strategy in all of the years of Chrysler factory training I received in the past. Lots of driveability classes in there BTW. Plenty of other boring details were covered but never once was anything like this mentioned in all those training classes.

Of course I can't prove that this strategy doesn't exist. That would be trying to prove a negative. So I ask, do you have any proof that this strategy does exist other than a brief aftermartket training group article? I'm talking about an actual Chrysler source.

Also you say you "have seen it behave otherwise". You have witnessed the PCM disable an injector on a misfiring cylinder? How did you know it was being disabled?

I will gladly admit I was wrong if you can prove it. I'm not that hard headed.

 

[atoman]

Also you say you "have seen it behave otherwise". You have witnessed the PCM disable an injector on a misfiring cylinder? How did you know it was being disabled?

It behaves exactly as described in ATG training material, if PCM detects repeated (hard) misfire on a particular cylinder it disables that injector pulse. It does not disable random/all injectors from random misfire... When you reset the codes (PCM) it starts with the pulse only to shut if off again as soon as it detects same misfire (until misfire condition is corrected)

If you know otherwise, it's fairly simple to pull off a plug wire and demonstrate with a meter or scope (or even a probe) that the sparkless cyl is still getting a constant injector pulse - no need in "trying to prove a negative"

Also, note that it says "most", meaning there could be outliers but all Mopars from mid 90's and up (since OBDII) that I've seen disable misfiring cyl injectors.

 

[Valhallalla]

It behaves exactly as described in ATG training material, if PCM detects repeated (hard) misfire on a particular cylinder it disables that injector pulse. It does not disable random/all injectors from random misfire... When you reset the codes (PCM) it starts with the pulse only to shut if off again as soon as it detects same misfire (until misfire condition is corrected)

If you know otherwise, it's fairly simple to pull off a plug wire and demonstrate with a meter or scope (or even a probe) that the sparkless cyl is still getting a constant injector pulse - no need in "trying to prove a negative"

Also, note that it says "most", meaning there could be outliers but all Mopars from mid 90's and up (since OBDII) that I've seen disable misfiring cyl injectors.

I have no desire to mess around with old and possibly fragile wiring and electrical connectors on my van to prove your point so I won't be doing the experiment that you suggest. I can only go by what you say. I have no reason to doubt that you have witnessed what you claim. I find your posts here to be straight up, honest and almost always helpful.

That said, I am still not convinced. The main reason is that in the many Chrysler training classes I attended over the years there was never a mention of such a cylinder deactivation strategy. I went through some of my old training manuals and still find nothing referencing this. There are plenty of other minute details about the operation of Chrysler's EFI and emissions monitoring systems but not the slightest mention of a cylinder deactivation strategy.

I find it to be remarkable and unlikely that Chrysler would withhold such information from their technicians when it would be very important and even critical in diagnosing problems on their vehicles. Sure, manufacturers will keep certain information proprietary. Something like this would probably not be kept secret.

So, unless you have some better documented sources other than the brief mention in the ATG article (preferably something from Chrysler) I will continue to believe that Chrysler did not employ a misfiring cylinder deactivation strategy.

 

[atoman]

So, unless you have some better documented sources

I'll let you spend the time and look for the sources that satisfy you, but before you say something categorical like:

The PCM does NOT shut down misfiring cylinders. I have seen others post similar statements here before. I don't know where this bit of misinformation originates but it is simply not true. The PCM will limit engine RPM in the event of serious misfire in an attempt to minimize catalytic converter damage but it does not shut down individual misfiring cylinders.

you better have some way or source to back it up...

BTW, some FSM diagnostic procedures do mention it, you just haven't read it or bothered to pay attention:

NOTE:
When a Misfire is detected for a particular cylinder, the PCM will shut down the Injector Control circuit for that cylinder.

Or right here..

 

[Road Ripper]

That's 5th gen with a totally new computer system. I also believe the 4th gen never implemented this. How else could you get hard misfires on vans with melted injector wiring, and they STILL fired away?

Our 2005 Dodge Magnum had cylinder deactivation on it's 5.7L V8 for fuel economy while cruising, and it also had the drive-by-wire throttle body. I think anything that came with that drive-by-wire throttle body had the newer computer system and thus, cylinder deactivation.

 

[atoman]

How else could you get hard misfires on vans with melted injector wiring, and they STILL fired away?

SBEC vans with melted injector harness caused ECU to loose control of injector pulse (and often burned out injector drivers)...
Injectors would short to ground and open wide or would short to another cylinder and 'fire' in pairs.

Again, the test is simple. Pull a plug wire off and see if it keeps the injector pulse going.
The ones I've had to troubleshoot, all disabled injector for the misfiring cylinder. I suspect it has more to do with the 8/80 federal emissions warranty than anything else (PCM, DBW, or comm bus) - what manufacturer would want to replace cat converters from misfiring engines if it can be easily avoided.

 

[Road Ripper]

I have the oddball 2004. Still has the problematic injector harness, but has an NGC computer - one year wonder. I do want to try some different experiments with it one of these days, so this could be another thing I fool around with.

 

[Valhallalla]

BTW, some FSM diagnostic procedures do mention it, you just haven't read it or bothered to pay attention:
https://www.justanswer.com/chrysler/9vek2-hav-problem-2014-crysler-town-country-3-6lt.html

Or right here..

Awesome. That's exactly the type of verification I was looking for. Straight from Chrysler's mouth. You have convinced me that the misfiring cylinder injector deactivation strategy exists on a 2014 minivan. Besides the fact that I don't own a copy of it, the main reason I have not read or bothered to pay attention to the 2014 FSM is because I don't have a 2014 minivan nor do I work on one. Why would you expect me to have read the service manual for a 2014?

Thing is, this thread is about a 2002 minivan. Does what is written in a 2014 service manual apply to a 2002 minivan? I don't think so. I can post about two dozen pages of the diagnostic procedures from the 4th gen FSM for the same misfire DTCs. This includes both early (SBEC) and later (NGC) systems. On none of those pages is there any reference to deactivation of the injector as a result of misfire detection like there is in the 2014 manual you cited. That implies to me that 4th gens don't have this strategy otherwise it would have been noted by Chrysler in the same way it was in 2014. Maybe you just haven't read or bothered to pay attention to the 4th gen service manual? Do I need to post the pages here or will you take my word on this? I really would rather not screenshot all those pages but I will if you insist.

I think we should call this one a draw. We are both partially right and both partially wrong IMO. I don't believe the strategy exists on 4th gen Chrysler minivans. So far I haven't seen anything to indicate that it does. I have no doubt that it does exist in 2014. You have shown that. Somewhere between 2008 and 2014 the strategy was adopted perhaps when engine controller types were changed.

And lastly, thanks. I learned something new today.