I have a 2000 Discovery 2 with 115k miles. It is a recent purchase and I am trying to work through the trouble codes. It has a PO301 cylinder 1 misfire. I have replaced the coil packs, spark plugs and wires. I have tested the fuel injectors and they seem to be good. The codes are as follows:

PO141 O2 bank 2 sensor 2 heater circuit
PO160 O2 bank 2 sensor 2 no activity
PO161 O2 bank 2 sensor 2 heater circuit
PO301 cylinder 1 misfire
PO327 Knock sensor bank 1

The knock sensor is due to a broken shield somewhere in the wire (not at either end) and I have a donor vehicle so I will probably just replace the whole ECM harness.

I ran a compression test with these results (which seems pretty good):
#1: 175 #2: 190
#3: 185 #4: 180
#5: 175 #6: 190
#7: 180 #8: 190

So having ruled out plugs, wires, coil packs and injectors, what should I check next?

 

Don't worry about the 02 codes unelss you have emission testing in your state, sensor 2 is just about your cats and it probably is just a bad sensor.

How did you rule out the other items? With a single cylinder code it is best to swap plugs, wires, coils, and injectors left to right to determine if the issue follows the component or stays in the cylinder. Your compression looks good, so I am suspecting it is an injector or plug wire.

 

I replaced plugs, wires, coils then used a spark tester to verify. When I unplug #1 it Idles rougher. I checked the injectors with an injector pulse tester and compared pressure drop with a fuel pressure gauge.
Today I looked at the O2 voltages. Before it warms up the downstream ones are steady at 0.445 volts. Once it goes closed-loop the bank 1 drops to 0.04. It seems like it might really be running lean on bank one after it’s closed-loop. Could that be? Maybe because the knock sensor is out on that side?

 

Stupid question, I just had issues with my coil pack personally. Took entire intake off and cleaned the surfaces new intake gasket upper installed coil pack verified correct wire routing by the book.

Still had a misfire after almost blew my top, cleared the codes misfire went away hasn't come back.

You have a scan tool? Or are you using a parts monkey's?


Also, have you checked for vacuum leaks and fuel injectors?

 

If your misfire code hasn't come back after clearing and several start / stop cycles, you are probably in the clear.

Yes, I have a scan tool.

I have checked for vacuum leaks by spraying starting fluid around suspect connections. None were detected.

I checked the injectors with an injector pulse tester and compared pressure drop with a fuel pressure gauge.

 

I have repaired the damaged knock sensor wire and replaced the O2 Sensors.

All codes are gone except still has PO301 cylinder 1 misfire. It has always just been Cylinder 1, never random or any other cylinders. What can it be?

 

Check plug and gap or it might be foweled.

Could be injector, valves, something specific to that one cylinder.

 

If you will kindly read the rest of the thread I have already ruled out plugs, coil oacks, spark plug wires, injectors,Vacuum leaks, and the compression is very good so doesn’t that rule out valves? People say the CPS can cause a specific cylinder misfire.

 

So to update, I have eliminated all codes except Misfire P0301. What I have done so far.

• Replaced both coil packs, Plug wires (STI 8mm), Plugs (Champion RC11PYPB4)
• Repaired a damaged driver side knock sensor wire
• Tested flow and function of all Injectors and injector wires
• Replaced all injectors
• Replaced CATs and O2 Sensors
• Checked for Vacuum leaks, found one - the manifold connection for Brake booster, Replaced fitting for that
• Compression test - all look very good (175 to 190 psi)
• Leakdown test - Cyl 1: 8% Cyl 2: 6% etc
• Replace Crank Pos Sensor

When I reset codes, I initially see P0300, P0301 both pending. After a few start / drive / stop / restart cycles it goes to just P0301. I've been watching O2 sensors. At start up, before closed-loop, they both read around 0.450. After Closed-loop as it warms up, the downstream gradually go up to around 0.750 and the upstream regulate as they should. This is while idling. Once it is warmed up and I drive it the drivers side downstream is all over the place and typical is around 0.075 while upstream is say 0.790. This I do not understand and it seems like not the expected behavior. The Passenger side seems pretty normal. If I stop driving and let it idle the downstream on both sides stay around 0.750 and upstream regulates.

I do not have a "hard misfire". The SES light is on but never flashing. It idles a little rough, but if I disconnect a spark plug wire, including #1, it gets worse. While driving it feels smooth.

Not sure what else to do. I have not replace MAF sensor, but I can see readings and seems to change normally. It does not seem like a stuck valve. I guess could be cam lobe worn off but seems unlikely.

Any ideas?

 

Your issue is clearly on #1 cylinder. Compression and leakdown look fine, so I suspect an injector or plug wire issue. swap the wire with one from another cylinder, if that does not change swap the injector, then plug, then coil pack. Inspect the wiring closely on injector #1.