I bought this used 2003 E250 cargo van in July this yr, it has 166k, 4.2L, former top's maintance van fully loaded.
1st got van was getting avg. 18mpg empty, put on a ladder rack & ladder & shelving tools and got avg. 16mpg

now avg. 10mpg

Ck Eng. Light came on, code po306 & po316 I think, misfire 1st 1000 rev. & misfire #6
So I changed the plugs & wires to bosch quad tip & napa life time Belden wires & cleared codes. 5 days later same codes again. So I changed the coil pack with a new napa #ic364.
2 days later same codes.

Took to muffler shop for repair, bad muffler and cracked pass side cat. Had both replaced.
Still same codes. Exhaust sounds tinny& loud, they ck again, told me front elbow cat’s burned out from dumping to much fuel, tail pipe very black & not to replace till problem resolved.
Sprayed carb cleaner all around intakes for vac leak, no increase in RPMs
Cleaned MAF with MAF cleaner, air cleaner filter good, fuel filter has 10k on it,
SEAFOAM added to last 4 tanks of gas
Cleaned carbon ridge off TB & held open & sprayed in SEAFOAM in to intake, also removed EGR sensor & poured SEAFOAM into EGR tubes & in to PVC hose & in to break vac line. Ran eng a few sec to draw in seafoam and then let sit 20 min. started motor revved up to blow out carbon till done smoking & repeated 2 more times. 2 days later same codes again.
I notice that 1 day sitting in a traffic jam for 10 min motor started running very rough. Put in neutral and revved up & it was ok then. When I start up it seems to be a little chugging till get going or rev it up, like it is fouling out. Running out of ideas to ck to fix. No other codes show,

 

Take a look at your crank sensor and the shutter section. Look for any possible looseness or contamination including the wires and connections. It's a left field shot, but might be worth checking out.

 

it like it's running rich... tried all 3 grades of gas.... best milage is with the lower oct. gas. thought maybe the tps, but no code for that showing.

 

Are you sure about replacing wires ? Doesn't it have coil on plug ignition?
If so, you may have a coil going south. Don't wait too long to replace if it does have COP ign. If left alone can take out PCM. A good scope man/woman can confirm how far this went.

 

no it's a 4.2 L v-6 , has a 6 pack coil mounted on valve cover

 

read a post on another site, same codes, thay thought was it might be the bosch quad tip plugs. but this was going on before i changed the plugs

 

The fact that it keeps throwing up cyl # 6 is something that should be checked further.
The entire system should be checked from the crank sensor to the ign module to the coils , wires and plugs. Try switching components between # 6 and another cyl to see if you can create that problem in another cyl. If you can get someone that knows how to really use a scope , they should be able to pick that up right away.

 

at this point i am looking for a ck list & order of things to look at and test before i go and just more parts in....
i would think the list would tell me what the test readings or results should be for each ck point.