Please Help With code Po336!

[Yellow2SS]

Hi all I usually dont post, just read all the good info here. I have a problem that is stumping me. The boss' 02 Denali XL AWD came in with a bad hesitation only when cold (below operating temp). It came up with a code P0336 CKP small error I think it is. Truck has 152,000 miles so I replaced crank sensor with an OEM sensor, no help. I ohmed out wires to ECU, all good. Changed ecu, same code.

PID's showed bank 1 LTFT like 8% over bank 2. I suspected a vacuum leak as this truck has the original intake gaskets. Sure enough found leaking gasket and replaced. Verified this was fixed as LTFT is good now.

I used a spark tester to check which cylinder is dropping out as I wasn't getting any misfore codes at all? It was always cyl 3. But, only cold, and only under a load, not while idling? I used dye in the coolant because these truck were known for head porosity a while back. I found dye in the valve cover, so I removed the head and sent it out for pressure testing. Head came back fine, they took a sliver off to straighten it. It looks like the head gasket was leaking also. Re-assembled and runs great, same miss, same code?

Checked crankshaft for endplay, within specs. this thing has me stumped!
I also changed coilpack on cyl3. As well as switching injectors around.

Now I have some other codes as well all of a sudden.

P0300
P0336 still
P1514
airflow not what expected HELP!
Thanks, Randy:help2:

[joecar]

Randy,

Ok, you've eliminated the easy things...

Do you have access to an automotive lab oscilloscope ( e.g. Picoscope from www.Autonerdz.com (http://www.Autonerdz.com) )... i.e. one which has a high resolution display (i.e. runs on Windows PC)...?

With this you can place the capacitive probe on secondary #3 plug wire and view the kV waveform... and then work back from there...

You could also see the CKP waveform and determine if the #3 portion (referenced to #1) of the waveform was mis-shapen... (bent reluctor wheel...?).

[joecar]

See example waveforms.

[modpcm]

Randy, the scope will help you for sure, if you don't have access to 1 you could try shimming the crankshaft sensor, add the shim between the engine block and the sensor bracket , try with .010 and see if better or worst, you might have a crankshaft bearing issue.

modpcm

[Yellow2SS]

Thanks for the responses. I will try some stuff in the AM. I have an old heath kit scope that probably won't help much. I have been reading up all day about autonerdz. I definately will buy one soon, thanks for the info.
I seem to get all the problems where I work. The vid about the jeep on autonerdz actually solves a problem on a jeep from last week!

I was already thinking a misfire could cause the code P0336 because of the crankshaft stalling during misfire. But maybe the misfire is valvetrain related?
I did comp and leakdown, but need to do running compression. I think this will solve it somehow! Also note the exhaust valve face on cyl 3 looked darker than the rest, so that cylinder was definately misfiring.

[joecar]

If you buy thru Autonerdz they will support you forever (including detailed waveform analysis)... they even support me (DIY'r).

The 2-channel and 4-channel kits they sell include a bunch of probes (voltage, capacitive kV, current clamps, back-probe pins, etc...) ready to go, well worth the money.

If you're an automotive technician/mechanic, you need a scope because it will save you time and avoids shotgunning.

[Alexo1us]

Just a quick guess since you rule out most other stuff did you check the plug in 3

[Yellow2SS]

Just a quick guess since you rule out most other stuff did you check the plug in 3

Thanks for the thought, I installed all new OEM plugs.

On another note, customer has had truck for 2 weeks, problem disappeared.
Seems like after all readiness tests completed, truck was okay. Customer reports perfect cold starts, great gas mileage, no problems whatsoever!

I'm still on watch with this one though.

[joecar]

Strange... :doh2::cucumber::banana::bangin::laugh:

[Yellow2SS]

Truck came back again for same code. I was determined to re-check reluctor wheel on crankshaft. Removed starter and crank sensor, couldn't see very well, so I also removed wheel well. They come out real easy, all plastic rivets, lots! Trigger wheel had no signs of damage or loosness.

I went to re-install crank sensor and saw flakey rust on one side of CKP hole more than other side. This was only visible because of removing fender liner!
I stuffed a piece of rag in hole and used a long screwdriver and a hammer to chip off rust. This took awhile to get it flat as other side of hole. I also wirewheeled hole with a small wire cup on a right angle die grinder.
The hole was now perfectly smooth.
Installed sensor, starter, and wheel well.
Reset all codes, and drove while still cold, no P0336!
Got one P0300 code, pulled over and relearned CKP because truck was now warm.
Customer reports occasional misfires, but no CEL!
I suspect another coil or bad plug wire. Truck is coming again next week for diagnosis of new problem. I use a HV spark probe to check for leaky/bad wires, should be no problem with CKP fixed.

Thanks,
Randy:rockon:

[joecar]

Randy,

So you suspect that the rust on one side of the CKP sensor bore was causing the sensor to move by itself...?

That is odd that there should be rust there...:shock:

[Yellow2SS]

Another update to this truck! Over a year later and here is the final solution. Customer was driving vehicle for the last year with the occasional misfiring only while cold. They decided to take to the dealer
for an oil change and one last check on the misfire. (previously this dealer had no solution to the problem) The dealer ended up replacing the catalytic converter and the truck is finally cured!
I can't believe I overlooked the converter. I figured I would post here to help others to learn.

Randy

[joecar]

Randy, thanks for posting back :cheers: