Plugs are a few months old. Problem originally appeared not too long after changing my plugs and wires during some maintenance last summer. I had installed iridium plugs so swapped in the copper hoping it would resolve the issue, which remained unchanged. Wires are 6 months old and I have swapped them around and it never moves the misfire. The wires are all receiving spark. Cap and rotor have been replaced 3 months ago trying to solve the issue.

 

If you can, I would be hooking up an o-scope to the crank sensor, and see what the output waveform looks like.

 

Is there a sensor or something in the transmission that could throw this off? I changed my transmission fluid and pan gasket in the service I did this summer shortly before it started throwing codes. Trying to think of what I could have boogered up.

 

Nothing in the trans is going to give you a misfire......

 

Sounds like it's time to let the mechanics at it with their diagnostic tools then. Darn!

 

Hello! I am back with an update.
I took the van in to the local mechanic to get a diagnosis on the misfire codes I've been unable to solve.
Misfires were present on most cylinders, most often 3 and 4. They attacked a vacuum gauge to the engine and saw that it is not holding steady vacuum and so diagnosed vacuum leak. Then they did a smoke test and could not find any external vacuum leaks.
Because of this they diagnosed it as an internal mechanical issue. The next step they said would be to remove the upper engine and service the heads to find the vacuum leak, I believe they mentioned sending the valves off for a valve job. They quoted me $3,500 for the next step which is what I bought the van for 8 years ago.
I am wondering what anyone on here might think about this diagnosis. What kind of internal mechanical problems could solve this; valves, head gasket, crack?
They told me I could keep driving it with bad idle, it just won't pass emissions, which is not an issue for me as I register the vehicle in Florida. Is this an issue I could continue to drive on for years? What does eventual catastrophic failure look like?

Thanks for any advisement. I am bummed it's a big fix but relieved I wasn't missing something stupid.

 

You could replace the heads with new ones for less than that......

If you have a compressor available to you, do a cylinder leakdown test. (Can probably borrow/rent the gauge set from a local parts store... I am rather surprised the shop didn't suggest that.....) That will tell you what kind of shape your cylinders are in, and where the problem is. If there is one.

 

There is a plate and gasket on the bottom of the plenum (intake manifold.) This is a notorious vacuum leak location, and it has its own TSB (TSB 09-05-00) for the repair. Assuming the rest of the crankcase related gaskets aren't leaking, cap off the PVC and breather hoses going to the crankcase, then connect a vacuum gauge to the oil dipstick tube and start the engine. If the gauge starts to show pressure, shut the engine down, you don't want that to go over 3 PSI. If the gauge shows vacuum, then the plenum gasket is leaking.

Here is a video that shows some of what I'm talking about.

 

Oops, forgot to attach the TSB to my last post, so here it is.

 

Okay. The ghost in the van keeps acting up!
I haven't had a chance to do the cylinder leak down test or manifold gasket diagnosis. I was waiting to get to a friends place with garage space and a compressor later this month.

Driving yesterday the engine stopped firing as I was driving down the road. Wouldn't start right away but I got it going in a couple minutes and was able to finish my trip. Since then the problem has been intermittent but mostly not working.
There is no spark coming off the ignition coil. Sparks intermittently return and engine runs.

I replaced the ECC in October after I had intermittent electrical failure, but in that instance I lost instrument gauges and dash read "No Bus." It is not doing that currently. No codes.

So options are this is a new novel problem OR related to the electrical failure in October but separate from the misfires OR it's all one problem.

Any help diagnosing this would be appreciated! Something electrical and upstream of the coil. I haven't been able to find anything looking off with the grounds or harnesses yet.

Ignition coil was replaced in December.
I replaced the crankshaft position sensor with Mopar in February.