Hello Forum, new guy here. My name is David. I have a 2003 Ranger with the 3.0 liter V-6 engine. Short cab, long bed. Rear wheel drive. Five speed stick shift. Truck has 198K miles, but I had a new Jasper engine and rebuilt transmission installed in 2018 (and a new clutch) so the powertrain only has 19K miles.

Lately I've been fighting with a persistent check engine light. The codes are P0316 and P0306, which respectively are Misfire Detected in First 1000 Revolutions, and Cylinder #6 Misfire.

Last year I gave the ignition system a tune-up. I replaced all of the spark plugs and plug wires and installed a new coil pack. I've actually bought seven spark plugs, because in the troubleshooting efforts since then I broke one of the new plugs and had to replace it.

I've moved spark plugs between cylinders. The problem stays on #6.
I've move ignition wires between cylinders. The problem stays on #6.
I've replaced the o-rings on the fuel injectors and moved the injectors from the left side to the right side (#6 swapped with #3). The problem stays on #6.

I have done a compression check. Cylinders 1, 3, and 4 all pushed 155psi. Cylinder #5 pushed 153. Cylinder #2 pushed 149. Cylinder #6 only pushed 135, so it’s a little lower than the rest, but still 87% of the best.

If I clear the code, I can drive the truck for several days (more than 200 miles) before it comes on again. The truck seems to run fine, other than the fault light. Maybe it's a little rough at idle, or maybe I am imagining that. All of my other recent vehicles have had eight cylinders.

I've checked the cam position sensor. It was actually installed backwards in 2018 (I was troubleshooting cylinder #2 for a long time before I figured out it had to be #6), but I corrected that. After the correction it started leaking oil, so I replaced it and again double-checked that I had the timing correct.

The truck had a new water pump installed not too long ago. I wonder if the crankshaft position sensor could have been damaged somehow during that action, but I can't imagine how that would only affect the #6 cylinder.

In short, I've put a LOT of thought into this and I'm all out of ideas. What else is there? What causes this combination of P0316 and P0306? Help please. I still have a little hair left.

 

Welcome to the forum

Good testing and troubleshooting

#6 has a burnt exhaust valve, #2 as well, just not as bad yet(the P0316)

Redo compression test to confirm
Cold engine
All 6 spark plugs removed
Test 1 cylinder at a time and write it down
4 cylinders with 153-155, and 2 with lower numbers means there is something going on with the 2 lower cylinders
The 10-15% rule was for much older engines, pre-1980s, that had marginal rings, lol
Newer technology has much better performance in that respect

3.0l Vulcan ran 9.3:1 compression ratio so has hotter combustion which also makes it more susceptible to exhaust valve issues, but any and all engines with valves WILL get burnt exhaust valves, thats why most have heard of the term "valve job", was and is a common failing in any engine that uses valves


Just FYI
Misfires codes P0301-P0306, P0316 are "time" codes
Computer works in milliseconds, thats how it works for pretty much everything it does
So it "knows" how long it takes for the crank shaft to spin 1 revolution at say 2,000rpm, its just math and thats what computers do best
If its a millisecond(or a few, lol) less then it "knows" something slowed down the spin, usually a misfire, OR a partial misfire(#2)
Full misfire adds no "spin" to crankshaft, partial misfire adds less "spin" than it should
Computer then breaks it down to when the slow down occurs, and takes a "best guess" as to which cylinder is misfiring, and with a Cam sensor its usually pretty accurate, Cam sensor spins at 1/2 the RPM of crank shaft so has better resolution to see the slow down

Changing spark plugs and wires and coil are easy to do and needs to be done over time in any case so not a waste of money
But compression test should always be the next step
Compression is black and white, mechanical, no grey area, yours shows a compression issue in #6 and #2, and since there is a P0306 code then compression in #6 is the issue

 

A burned exhaust valve in an engine with just 19K miles? (Naturally, it's just out of warranty.)

 

Happens on new engines
Most common cause is valve stops rotating and gets a hot spot and warps a bit, which allows explosive gases a way out and that eats away at the valve and seat, even if valves starts to rotate again damages is done
Another is carbon build up, rich running, it creates hot spots causing pre-ignition which eats away at pistons and valves
Installation defect, mismatched valve and seat angles
Manufacturing defect, unseen crack in seat or valve


Google: Exhaust dollar bill test

See if you get the sucking in of the bill at tail pipe
A spark or fuel misfire just won't push the bill out like a cylinder that fires
A cylinder with burnt exhaust valve won't push the bill out as well but will also suck air from the exhaust back in as its piston goes down on intake stroke