What is the service history of the truck?

Were your O2 codes P017xx series?

Did you inspect your ignition components on cylinder 1 and 2 after your truck threw P0301, P0302 codes?

I'm jumping the gun here, but I'm gonna guess you need a tune up.

 

Thanks guys,

ProjectSHO89, I read about some tests I can do using a multimeter. To your knowledge, can I discern the same info by watching voltage changes as I could with a diagnostic computer?

Patman, no there were 6 codes in total last time I checked. The original ones were for banks one and two oxygen sensors. The second time I checked, immediately after it began to run rough and my SES light flashed, it also gave codes indicating cylinder one and two lean condition. Is it true that it won't throw codes if my SES light isn't on? I'm driving it waiting for it to come back on so I can check them again.

Really appreciate everyone's help!

 

Hi AndersonS,

I got the truck appx. 4 years ago when it had 30k mi.
Since I've had it, I've watched fluids, changed my oil appropriately, as well as air filters, cleaned MAF with each air filter change, kept battery posts clean. Maybe it is time for a tune-up, but I want to point out that it didn't slowly progress to running rough. It was pretty much perfect until the day I checked my codes he second time, when it began to run rough.

 

Depends on fast your meter is.

 

Ok so oddly the rough idle seems to have improved a little, now it's mostly when accelerating. SES light is still not on, checked for codes anyway and they are:
P0171 bank 1 system too lean
P0174 bank 2 system too lean
P1000 OBD II monitor/ drive cycle test not complete
Now I am also getting a really soft little 'pop' occasionally that I can just barely feel through the gas pedal, and always when accelerating or going up a hill.
Does that info shed any light on my problem in anyones' opinion?

Thinking the sea foam might have cleaned things up a little (added to gas), and that the p1000 code is there because I haven't driven sufficient distance since I disconnected the battery to clean the terminals

 

Lean codes both banks is usually a vacuum leak. Seafoam is rough on cats, use Techron or one of the Gumout products with PEA.

If you have 87k on the original spark plugs, it's time to change them.

The 4.2's with the plastic intake will need new plenum gaskets and isolator bolts eventually, maybe yours are due.

 

Thanks glc!

 

Ordered new plugs, wires, and coil, should have them in within a few days. Didn't see any arcing, but the issue is only evident at speed when I can't be under the hood.

Checked codes again and had:
P0174- lean B2
P0136- misfire on stsrtup
P0301- Cyl 1 misfire
So seems that it's shuffling between bank 1 and 2 being lean, and cylinders 1 and 2 misfiring, according to these and previously retrieved codes.

Then, a few days later when I could get back to it again...
I changed the oil and used a spray cleaner (sea foam brand I believe-- I know you told me it was bad for cats but I already had it and no ride to the parts store) through the intake manifold at the throttle plate, and after all the smoking was done it seemed better for about a day. Also looked for vacuum leaks using carb cleaner

Had as a new wrinkle yesterday. Took our hounds for a run out in the country and that involved driving on a badly washboarded gravel road for a while. Once I got back on to he highway, I noticed that it seemed to be running better, so I gave it some gas. Accelerated strongly and perfectly up to 75. 5 minutes later it was back to the same symptoms, missing, struggling to provide power going up hills, but still running fine at idle and speeds less than appx 25 mph. That makes me think it could be a bad connector somewhere? What are your thoughts on that? The only one that seems weak is on the alternator, where one wite comes out of the connector harness and reconnects to the alternator by itself in a different spot. Seems like I read that a failing diode in an alternator can cause the same issues; can anyone expound on that or tell me what that wire is connecting to within the alternator?

 

must have ran out of room or something...

used carb cleaner to probe for big obvious vacuum leaks, and didn't find any. I know that to find one that way would be 'to get lucky' and that there's better ways to do it.

 

carb cleaner is tough on rubber hoses.

 

Got my new plugs, wires, and coil put in today and the problem seems to be fixed!
Old (original) plugs didn't look too bad, especially the cylinders that I was getting misfire codes on; wires look ok too. So must have been the coil.
I used single platinum (Denso 4511 twin tip) plugs; think I'll be ok with those? The retailer's amazon page that I ordered them from said they were for my 03' 4.2L, and it wasn't until I became curious about the reason for the different plugs in each bank (waste spark ignition system-- interesting!) that I did a search and saw all the posts here about needing to use double platinum plugs or fine wire.