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C. Walker, Jr.
C. Walker, Jr., Auto Mechanic
Category: GM
Satisfied Customers: 711
Experience:  Shop training and experience.
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I have what seems like oil leaking out of my charcoal

Customer Question

I have what seems like oil leaking out of my charcoal canister at the connections in my 2005' GMC Sierra K1500. I don't know which one it is exactly, but I'm leaning towards the bottom connection. I also have code P0332 which I replaced both knock sensors with AC Delco knock sensors and a new harness, and built a dam around the caps. No other codes showing, but P0332 keeps coming back. I have looked everything over 3 times, and can't come to any conclusions. I did notice this leak while staring under my truck in frustration. I don't have any codes for evap leaks, but my truck does seem to hesitate which frustrates me even more. Feels like the truck is lagging big time. Any help greatly appreciated, as everything I research on the web has nothing related to my issues.
Submitted: 1 year ago.
Category: GM
Expert:  C. Walker, Jr. replied 1 year ago.

Good afternoon, Disconnect the two pin connector on top of the intake, it should have Blue wires. Ohm each wire to ground on the knock sensor side. They should have resistance between 93K-107K ohms for each wire. If not in specification, remove the intake manifold and check the connections and wiring to the Knock Sensors . If they ohm tested OK, verify the wiring to the Powertrain Control Module is not open or grounded. If OK, tap on the exhaust manifold with an extension while monitoring the ac voltage produced by each sensor. If the sensor does not produce a good voltage compared to the other sensor, re-replace the lower output sensor. Be sure to torque the sensor properly, over-tightening can damage a new sensor. Tighten to 15 foot pounds (20 Nm). If the code is coming up than I am sure it is throwing off the timing like it should causing your running problems. As for the problem with the leak that is what it looks like if the fuel tank got topped off and the excess gas is slowly leaking through the charcoal canister.

Customer: replied 1 year ago.
How long is that leak supposed to take to clear up? This has been going on since October 2015. I never squeeze in gas once it clicks off. Most current leak is yesterday with less then a quarter tank of gas. It doesn't smell like gas, and to the touch it feels like oil. The stains it leaves on the ground stays for a few days at least. If it were gas wouldn't it evaporate at a much quicker rate?I will ohm each wore out and see what the readings come out to.Thank you for the reply.
Expert:  C. Walker, Jr. replied 1 year ago.

If it was oil it would never evaporate. But there should not be any oil in your fuel system. So it is possible that you have a leak on the engine and it sprays back to the canister from the fan and just the angle of the leak.

Customer: replied 1 year ago.
Engine is completely dry, top and bottom. Just once around the block it forms a little drop on the canister or hard lines. No where else under the cab or frame is wet.
Expert:  C. Walker, Jr. replied 1 year ago.

I would replace the charcoal canister. It does not sound good. This can cause issues with the emissions system making problems with it running as well. It should always be dry. Sometimes they get contaminated and if that happens we replace them. I would say it is a combination of some old gas and the charcoal canister. It would be a good idea to do this soon.

Customer: replied 1 year ago.
Since I'm there, Should I replace the evap vent as well? I don't have any issues with filling up gas. I have to remove the charcoal canister anyway for another install, that's what lead me to start digging around to see what was the problem.
Expert:  C. Walker, Jr. replied 1 year ago.

It would not hurt just to ensure you do not have it fail in the near future, they can fail over time from normal use. The vehicle is 16 years old and it could be on the end of its lifespan.

Customer: replied 1 year ago.
True. Both hub assemblies were talking not to long ago so I just replaced both of them. Original hubs. Truck has 116k on it, but I put less then 20k miles on it in the last 6 years. I'll get this going then. Hopefully it resolves my issue.I forgot to mention. The knock sensor code doesn't always come on. It has come on a total of 4 times since being replaced. But it seems like the time between each one gets longer after clearing it.
Expert:  C. Walker, Jr. replied 1 year ago.

The knock sensor code will only come on if it sees the fault several times. It will for sure retard your timing to protect your engine causing a very poor running condition. You can let it go but this is kind of annoying if it keeps doing it.