P0300 and C121C Problem - '06 XK 3.7L

[FLYCAV]

Here is what happened.

Driving on the highway doing around 76mph with the cruise control on, the check engine light and traction control light both came on. There was not any real indication from the motor that there was anything wrong at first. I turned off the cruise and slowed to about 70 mph. The rest of the way home the trans would shift down when going up slight inclines or if I tried to accelerate and the engine rpm's would jump to about 3200 and the egine light would flash and ding until rpm's were back to about 1500. If I slowly applied gas pedal I could get back up to speed no problem. If I tried to accelerate quickly the engine light would flash and acceleration would be slow.

After I got home I plgged in my Hypertec tuner and got the following codes P0300 (multiple engine misfires), C121C (torque request signal denied) and there was one other code B3004 which I think is the back hatch open which apparently was unrelated and must have already been in the computer. The next day I drove around town only, no highway driving and things seemed to be back to normal. The following day my wife and I went on an errand in town and then got on the highway to head to the next town to pick something up. Accelerating on the onramp I got the engine light and traction control light again and about got hit by a truck because I couldn't accelerate fast enough. I tried to take it easy on the highway and couldn't get much over 60. On the short ride home the engine was misfiring and I barely made it off the highway doing about 50 mph. Off the highway, at low speeds acceleration was getting worse and ended up stalling at a stop sign. We pushed it to the side of the road...got a lift home...returned with my tuner and zeroed out the codes. This time it didn't help much. I stalled or turned off the vehicle several times because the engine was shaking so much and pressing the gas pedal resulted in no rmp response. Finally got it home and coasted up the drive.

I had done a little research on the the forums about problem after the first day I had the issue and I ordered a new crankshaft position sensor (CKP) and a camshaft position sensor from RockAuto.

I replaced both sensors, reset the codes. After starting the engine light came back on and the engine was running rough (shaking). Turned it off, cleared codes, removed and reinstalled the CKP, still running rough and engine light came back on. Tried it again and unplugged the neg battery cable for a bit to maybe clear out the memory as well...still no improvement.

I also saw on some of the forums that a bad throttle position sensor could also be a contributing factor/cause of this, so I have one on order to come tomorrow. In the meantime I thought I would change the plugs (and see how they looked). So while I had the CAI off and the airbox attached to the throttle body, I noticed that there was a small amount of engine oil that came through the exhaust recirculation hose and ran out the bottom of my K&N CAI filter, See pic below of how much leaked (and the hose.)



Not a whole lot but enough to make me concerned that it was in the air intake. The plugs with only about 5K miles on them were really fouled up with black carbon. The pic below shows the plugs. They are in order as they would be looking into the engine compartment. The plugs on the drivers side seem to be worse than the passenger side and the back one seemed to be the worst.


The inside of the throttle body was surprisingly clean...just a small amount of oil mist. It wiped completely clean with a rag without cleaner. I also used electrical contact cleaner on all of the connections while I had the plugs out and even took apart and cleaned the sensor plugs and computer plugs.


Here's the question(s).
1. Based on the the faults and progression of events, does it seem like I'm headed down the right path to fix it?
2. Is there something else that could be at issue?
3. Is the oil in the intake a cause for alarm?
4. If the throttle position sensor doesn't work after I get it on tomorrow, what would you recommend next?

Thanks in advance for your help.

[FLYCAV]

Just got the new throttle position sensor installed and the air intake all put back together. Still getting the P0300 code and engine is running a little rough. I'm at a loss now. Anyone have any ideas?

[criket]

Going out on a limb here but on the Liberty's and on the Liberty forums, the 3.7 V6 has a problem of breaking valve springs, weak valve springs, etc. on valve springs. One of your Intake valve springs could be broken or worn so bad that the Intake valve isn't closing properly and could be throwing the miss fire code.

Of course that's a big if. How are your coils on each cylinder? Could one of some of them be bad causing the miss fire?

[Matt]

P0300 is not a good code to troubleshoot on electronically controlled ignitions. More often than not, its an ECU issue when the plugs are fouled like that (otherwise normally a fuel supply issue).

Did you put new plugs in?

Have you changed the PCV valve? That seems like a log of excess blow-by in the intake.

[FLYCAV]

Thanks cricket and Matt for the replies. In addition, I switched around my ASD relay with another relay in hopes that maybe an intermittant relay was causing the interuption in fuel, but it didn't work either.

Going out on a limb here but on the Liberty's and on the Liberty forums, the 3.7 V6 has a problem of breaking valve springs, weak valve springs, etc. on valve springs. One of your Intake valve springs could be broken or worn so bad that the Intake valve isn't closing properly and could be throwing the miss fire code.

Of course that's a big if. How are your coils on each cylinder? Could one of some of them be bad causing the miss fire?

I hope it's not something that serious. I'd think if it was a bad spring or a bad coil that it would throw a specific cylinder code rather than the general P0300 code, but I'm not sure how the computer actualy identifies a misfire. I can't imagine multiple coils going bad at the same time. Although lately I'd believe almost anything.

P0300 is not a good code to troubleshoot on electronically controlled ignitions. More often than not, its an ECU issue when the plugs are fouled like that (otherwise normally a fuel supply issue).

Did you put new plugs in?

Have you changed the PCV valve? That seems like a log of excess blow-by in the intake.

I did change the plugs but not the PVC valve. I did run out tonight and picked a new PVC valve from O'riely's, I'll swap that out in the morning (I like the cheap fix options).

As far as it being an ECU issue, would that be fixed by reloading the factory tune (I was running the Hypertch tune) and in this whole process have reprogrammed a few times both the factory tune and the Hypertech tune. -OR- would a dealer have to reflash it? Or is it possible that the ECU itself is bad and needs replaced?

Matt, when you say fuel supply issue, are you thinking fuel pump issue? or injector issue?

One other thing I saw somewhere was that carbon buildup on the exhast valves can prevent the valves from seating and sealing completly and create the problem. Compression testing could help identify this issue. You don't happen to know what the cold compression numbers should be on a 3.7 and how much variance between cylinders is within standards do you?

Thanks again for the help.

[Matt]

I would definitely load the stock tune before doing anymore troubleshooting.

Normally ECU issues that result in P0300 result in an new ECU, not just programming.

Fuel supply issues could be anything from pressure bleed-off to the pump going bad. Doubtful that its an injector issue because you have a better chance of getting struck by lighting while you're on your way to collect your mega millions lottery winning than you are to have multiple injectors go bad at the same time to cause P0300.

I'm not sure what the compression numbers are off the top of my head.... but that engine would have had to been neglected for a long time for carbon buildup on the valves to do this. Again, it would have to be multiple valves at the same time to foul all those plugs.

How's your oil level?

[FLYCAV]

How's your oil level?

Oil level is good.

......... because you have a better chance of getting struck by lighting while you're on your way to collect your mega millions lottery winning than you are to have multiple injectors go bad at the same time to cause P0300.

I just wish the odds of winning the Mega Millions jackpot were more like the odds of my Jeep throwing a P0300 code on the way to pick up a 12 pack.

Normally ECU issues that result in P0300 result in an new ECU, not just programming.

I was afraid of that.

Fuel supply issues could be anything from pressure bleed-off to the pump going bad. Doubtful that its an injector issue because you have a better chance of getting struck by lighting while you're on your way to collect your mega millions lottery winning than you are to have multiple injectors go bad at the same time to cause P0300.

I just might have to invest in that service manual afterall.

[Matt]

Use this
https://dl.dropboxusercontent.com/u/...2005-WK-SM.pdf

[thance]

Use this
https://dl.dropboxusercontent.com/u/...2005-WK-SM.pdf

Do you know of a similar link for a 2010xk?

[Matt]

No, but they're practically identical except for the body and accessories.