Darren Jackson

I've posted in the "Ask the Question" thread but I figure I'll make it a little more visible for other people by making a thread anyways.

I bought a 2000 Jeep Cherokee Sport, 2WD 4.0L automatic, that has a dead miss on cylinder 6. It has a constant P0206 OBD code that has survived a new connector going to injector 6, a tune up, electronic cleaner on everything, and even new injectors and a computer reset. My dad and I are lost and the only thing anyone else can come up with is a new computer or a new wiring harness.

Anyone have any other suggestions? Tips and tricks? I'm hoping to get it fixed soon so I don't end up with a fouled plug and the nightmare of pulling the coil off again. Thanks!

Sandyman

What I have read about this leads to the probability of a bad ground. Hope it helps.

Check for the following conditions:
The ignition feed circuit in the wire harness between the fuse and the cylinder #6 fuel injector for an intermittent open.
The cylinder #6 fuel injector control circuit between the PCM and the injector for an intermittent open or short to ground.

Radi

You replaced the coil pack, or not?

cruiser54

2 things, both related to carbon under a valve.

Get a can of BG44K and add it to a full tank of gas. Drive til it's down to 1/2 tank. Fill the tank again and then drive til near empty. Refill with gas.

Another alternative/supplement, and what I would do first is use water to break up the carbon.

Pretty easy.

Get a cup of water, preferably something like a 24 to 32 oz. cup.
With the air cleaner off, hold the engine RPM at 2000 RPM or higher and dribble the water from the cup, which you've pinched to look like a spout on top, into the carb or throttle body. Go slowly and the engine will bog a bit. Stop and let it recover. Repeat until the cup is empty.

Darren Jackson

If it was P0306, a missfire code for cylinder 6, I'd know it was carbon or a burnt lifter or valve or something, but it's just P0206, which is a malfunction in the injector circuit for cylinder 6. I'm going to check the ground wires and everything because my fuel level sensor doesn't work either after a new fuel pump, so it could be a faulty ground. I'll check back in later.

CCKen

Look for a chafed wire loom coming out of the end of the fuel injector harness plastic manifold where it exits the manifold and curves up to the main loom. There have been many occurrences of the loom chafing on the end of the fuel rail and in to the wires within.

Darren Jackson

New question. Does the distributor/camshaft position sensor (searching for either seems to bring up the same part, curious, I know) send the signal to the injectors instead of the sparkplugs on this model jeep? As everything I've found says that the Coil pack covers the job a normal distributor would on my model. This is confusing.

CCKen

The 2000 XJ uses the Camshaft Position Sensor to time the fuel injectors only.


Unlike the distributor type 4.0's, the 2000 doesn't need the cam sensor to time the ignition, the CPS does all the work based on the three sets of slots on the flexplate to signal which sets of cylinders are in line to fire.


As the slots pass under the CPS they trigger a pulse thru the CPS to the PCM. The PCM coil driver provides a ground to the coil pack to fire the appropriate set of plugs.


Slots visible in this view:

Darren Jackson

So it is possible that the camshaft position sensor is worn in such a way only cylinders 1-5 are firing?

CCKen

Not likely.


If you have a fuel injector issue on just one cylinder and there is power going to the injector, more than likely it's an injector driver circuit problem between the injector and the PCM, or the PCM. Unless, of course, the injector is bad.


If you test the injector with a Fuel Injector (Noid Light) tester and circuit seems to be working, test the resistance of the injector with a digital Ohmmeter. It should measure around 11 to 12 Ohms pin to pin.