Truck is a 97 Dak with a 5.2 and about 176k on the clock. These codes popped up randomly about 2.5 months ago while driving home using cruise control with the RPM's above 2K, so I believe the truck was in a closed loop.

• P0300
• P0302
• P0303
• P0308
• P0305 (About 20% of the time)

I have replaced the following components:

• All 8 spark plugs
• All 8 spark plug wires
• Distributor cap
• Distributor rotor
• Cam sensor (distributor pickup coil)
• Crank sensor (this was replaced in February when we dropped the trans since I broke the original. This is the only component I haven't checked recently.)
• Ignition coil
• Fuel injectors on cylinders 2, 3 and 8 since those are the same 3 that pop up each time it throws a code
• Replaced K&N intake as the plenum was cracked on the old one
• Catalytic Converter (this was needed anyway since the catalyst inside was broken and rattling.)

Things I've done so far:

• I've done a compression test on the affected cylinders and they all tested between 150-170.
• I've changed brands of fuel.
• I've ran injector cleaner through a tank of fuel.
• I've seafoam'd a second tank of fuel as well as ran it through a vacuum line.

Once I clear the codes, I can sort of "trick" the ECU by never cruising above 2k. This will delay the light but it inevitably does come on. I'm about at my wits end here and not sure what to check next. Is the emissions system my next section to tackle? Any recommendations or ideas?

Thank you in advanced.

 

On the cam/crank sensor, be sure to use only OEM sensors. Some of the aftermarkets don't work properly.
How's the vacuum? You could have a possible intake manifold leak.

 

What spark plugs did you put in there?

 

NGK Iridium, same things I’ve been running for years.

Didn’t use direct OEM replacements.

Vacuum seems strong. I pulled the line going from the intake manifold to the brake booster last night and had significant suction.

 

Replace your crank sensor with a mopar one, and replace both upstream O2 sensors with NTK's.

1-8-4-3-6-5-7-2

You are misfiring on 8, 3, 5, 2 all 90 degrees apart.

Being RPM activated tells me it's the crank sensor being lazy, as usual with box store ones, BTDT. If you've never done the upstreams, those will also give you fits of a similar type.

 

You know, I never thought to check the firing order against the misfire codes, kinda feel like an idiot for not seeing the correlation. That crank sensor is the only RECENT thing I haven't replaced so it makes sense to go there.

And I wanna say I replaced BOTH of my O2 sensors in... '18? Maybe '17? But I could be mistaken. Either way, I'll get replacements ordered tonight.

Thank you for the advice!

 

On the 02's, do not use Bosch!!! Dakota's hate them with a passion.

 

These engines don't really care for the rare-earth plugs either. They tend to induce some odd problems, like, mystery misfires....... Plain jane copper plugs are actually best.

 

In my experience, everything that's NOT an 02 Dakota hates the Bosch O2 sensors too. Cheap sensor that ONLY clears the code.

 

and a Bosch 02 don't clear the code for long. I had a 97 Wrangler with the 4.0 that ate an upstream 02 a year for 4-5 years (I had it from 2000-2019) and IDK what brand I used, I know it got a Bosch at least a couple of times, took what the parts store had/ but once I started paying attention to what brand I was using and put in an NTK it stopped. I could smell the exhaust for a couple weeks before I got the code--- which I didn't always get even when the exhaust started smelling different. but every time a new sensor would cure the bad exhaust smell for a while.

and your problem sounds much like what I had (to start out with) on my 360 powered Durango. I would occasionally get a couple others cylinders in the mix, but I fought a P0306 for a year. for the 1st 8 months or so of that year it ran great, didn't feel a misfire at all, despite codes. but I; replaced cap/rotor/wires/plugs, converter, crank sensor, distributor pickup, and 02's (all but wires and converter, on that list, more than once) I'm sure I replaced more than I say, it's been like 5 years. and I ran it with scanner in place with the original engine, I do not remember which, over/under 1000 RPM, I wanna say it was "above" 1000 RPM never had a miss; below that, the scanner misfire counter was going nuts on tracking #6 misfire, by now it was starting to run like it had a miss.......
I forgot something, somewhere in here I sent the computer out for a rebuild, was told there was a chip that was known for solder joints coming loose, the computer reman company told me that this could have caused my initial #6 misfire, and that they saw this component loose on the circuit board often on Dodge computers.
replaced #6 injector
swapped wires, plugs and injectors to other cylinders, and the other cylinder that recieved any parts swapped over from #6, never showed a misfire with #6's parts in another slot.
flushed fuel rail, tested fuel pressure and compression. results matched yours. no change in code or how the engine would run.

I took the injectors to a Bosch certified fuel injection place and had them all (including the old, replaced #6) for flush/test/rebuild, came back as being fine after a good cleaning

I finally wound up pulling the engine (by now, it started getting a little bearing noise/ truck had 258K on it, fought issue with misfire from 250K on) I swapped the original 360 for another that I had done a complete rebuild on. machine work and everything./ that turned into a fiasco of its own. (story for later)

Went to CL and bought a 360 with about 1/2 the miles out of a wreck. this was after being a garage ornament for 3 years because I was so mad at it.

Put on the of brand new EQ heads on the CL sourced engine, that had 3 hours (at most) and 6 miles run time on, from the rebuilt engine, after a trip thru the machine shop for a valve job and bent valve replaced.
and I replaced all new gaskets except rear main. Replaced all freeze plugs. put a set of 4.7 injectors onto the original 360 rail. new double roller chain. new fuel pump in tank. new water pump, all new tuneup parts again. transferred the new crank sensor and cam sensor (distributor pickup) from the rebuild to the CL engine. Bought the Hughes plenum plate, stuck that on there along the way.

I'd paid $900 to start off with for those EQ heads when I bought them for the 1st rebuilt motor. Brand new in the box, I picked them up at EQ's warehouse off the dock in Chicago, myself.
been back together for 15K miles and counting. finally so far so good. I still have the original engine and the 1st rebuilt one sitting here. had other problems with original injectors (freshly rebuilt, transferred from original; engine to rebuilt one) and some sticky valves in them brand new EQ heads...... "ready to go out of the box" they said//// BULL $#!T! I spent another $200 on a valve job on a set of brand new heads with 2-1/2 hours and 6 miles' run time...... #4 exhaust stuck open and kissed piston on newly rebuilt 360/ melted down a brand new cat. had to replace that again.
Upon putting those original but rebuilt injectors on the CL engine I discovered that at least 2 of them had been stuck wide freakin open. (that, plus the sticking valves in those brand new heads, was what killed the rebuilt engine) so those injectors weren't, in fact, "good to go" as the BOSCH place had told me they were.