I sincerely hope this isnt a double post. My last attempt seemed to vanish when I tried to preview my post. Grrr.
I apologize for the length, but I have a lot to tell.
For over a year my van would occasionally die at stops or slow speed and start right back up. This got worse, to the point of multiple starts to get out of a parking lot. OBD codes for #6 misfire and Primay/secondary ignition coil. Did full tune up. Plugs,wires, cap and rotor. Cleaned gunky throttle body. Same codes. Replaced ignition coil. Same codes, same problem with dying. Replaced throttle position sensor and idle air control valve. Same same. Held paper over tailpipe and got some suck back to tail pipe, as I understand it thats burned or sticky valve. Cleaned engine with seafoam, got an exhaust leak but no improvement. Found and repaired a vacuum leak. NO IMPROVEMENT. Removed outer wrap on wire bundle, looking for corrosion (115 splice). Wires look good. They are high in engine compartment and out of road splash. Had an old battery, it tested bad (even tho it always cranks) and replaced it. That is the work I've done up to today, over the course of a couple of months. The van would run fine for up to 3 days, then die out some more. It might work fine on the way to work, but throw serious fits on the way home. It got harder to restart, lots of cranking, sometimes waiting for a couple of minutes before it would start. Sometimes a little accelerator seems to help it re start, but I might get some backfire as well. Lately it has bucking fits on the highway. If you're still with me, you can see the sorry state I am in. Anyone have a flash of insight for me? Other than sell it as a POS?

 

What year is this van and which engine? If I read this correctly, the battery was eventually replaced but now were the cables or the terminals replaced as well? You can easily lose 2v due to bad cables/terminals. You need to read a solid 13.5 - 14 volts. Voltage that drops below 12.5 will cause intermittant and erratic issues thanks to the PCM or ECM. These vans are well known for wiring/connector issues and bad ground wires are very common.

Backfiring is always a bad sign, and in truth this engine may just be whipped. However much of what you've describe sounds to me like it could be fuel starvation. The fuel filter is not replaceable, the fuel pump is mounted in the fuel tank and the entire unit will have to be replaced. But before I did alll that work I'd suggest borrow/buy a fuel gauge and check for consistent fuel line pressure.

 

Fuel pump, filter or debris in line. Fuel injectors clogged? Also, replacing parts does not gurantee that they work in our disposeable economy.

 

Sorry, forgot that info. 1998 Dodge Ram van 3.9 engine. The terminals and cables look great, but I can go back tomorrow and have them retest. Can a fuel pump go out so very slowly? I though they went all at once.
I left out the fact that I pulled and cleaned the injectors as best as I could. The cleaner did pass thru them all. I swapped the one on #6 and still have the misfire.

 

Yes. The filter could be clogged and or the pump seals may be failing. It is a very common point of failure on these vehicles.

 

I had the same problems when I first got my van...

New heads and a new PCM later cured the issues...

Good luck.

 

Ok, I have a pressure gauge lined up for tomorrow. My problem, whatever it is, is intermittent.How do I take that into account? Do I have to test it AFTER the engine dies, before, or both? The videos and articles I've seen assume the vehicle will not start because the pump is completely out.

 

You are looking for a drop in fuel pressure that happens concurrent with your poor running issues. If it fails to start at all this could may be due to the fuel pump relay. In that case, read the sticky and bypass wire your fuel pump relay and run it directly.

The fuel pressure needs to be monitored while the van is running so you can determine if the stalling or sudden loss of power is due to sudden loss of pressure (no fuel). There should be a connection on the fuel rail that allows you monitor fuel pressure during operation so you will see this happen while driving.

 

Back again with more results and or the lack thereof.
I have had a fuel pressure gauge on for 2 days trying to catch the engine when it has one of

it's 'little moments'. The fuel pressure looks good @ 48-50 PSI. I get this reading after

turning key on (engine off) several times. It doesnt change a hair when I start the engine.

No drop even tho it has vacuum assist (or whatever the right term is). Cant find any more

vac leaks , btw. Lots of running time and test driving with no 'fits'. Started cold today

and the engine died multiple times on start up with NO DROP in pressure. If I give the

smallest accelerator the engine picks up and runs. So far it wont die out at stops for me

like it has done so often for me to get a reading at that point, will keep trying. Currently

no CEL. Can go for a while before I get a code again, when it comes back it is Fault:01

Pend:00 Po306 01/01. I have the list of things that can mean besides #6 misfire. What I dont

know and cant find online is the meaning of Menu item 3 I/M. It reads Misfire->Ready and

Fuel->Ready. Does that mean no misfire in #6, the issue is something else on the list? And

no detected problem in the fuel system? Would that include fuel relay , regulator or return

fuel line?

A code P0306 may mean that one or more of the following has happened: Faulty spark plugs or

wires Faulty coil (pack)---plugs wires and coil pack replaced. Coil pack warranty replaced

again yesterday now no coil code comes back.
Faulty oxygen sensor(s)--Ho2s->ready but O2s->not ready. One oxygen sensor is good and one

bad? Will that cause engine stalls or just bad emissions? Faulty fuel injector(s)--Swapped

fuel injectors in #6 with no change, code comes back. Burned exhaust valve--Trying not to

think about this one for now.
Faulty catalytic converter(s) --reader says Cat ->not ready but cat converter was replaced

in last 2 years, no rotten egg smell and no significant loss of power like last time.
That leaves Stuck/blocked EGR valve / passages
Faulty camshaft position sensor
Defective computer
Thought? Ways to test remaining possibilities? Or do I have to bit the bullet and pay up to

$160 to have a place test all these things?

 

The fuel pressure test went well, so I think you can now eliminate that as your issue. The bad news is that after reading all this info I am starting to think Funair02 is right. Unfortunately cracked heads/burned valves are extremely common on 3.9L. As the engine warms up that crack in the head expands and contracts which causes the intermittent operation issues.

It could be the PCM (computer) as well. If it runs absolutely perfectly hot but has a hard time restarting and only has issues when its cold, that could be sign your PCM is failing. If warming it with a hair dryer for 15min (when cold) restores normal operation and it starts right up and runs well, that is a sign the PCM is dying.

The good news is that the PCM is easily replaceable and they are available online for $130 - $275 depending on warranty.

The bad news is that rebuilt 3.9L cylinder heads aren't very cheap and the labor cost will be even higher.

Stuck/blocked EGR valve / passages - no
Faulty camshaft position sensor - no
Defective computer - possible
cracked cylinder head, burned valve - very likely