Number 8 cylinder throws code P308, and has a knocking sound now...
Asked by JBSchlem Apr 06, 2017 at 09:08 AM about the 2001 Jeep Grand Cherokee Laredo 4WD
Question type: Maintenance & Repair
Had some one "repairing" our 2001 jeep Laredo, but when it
was returned there was a knocking sound from the engine.
What could be causing this and how do I fix it?
4 Answers
https://www.obd-codes.com/p0308
Hornet_2497 answered 7 years ago
Code P308 means misfire on cylinder #8. On this 4.7 V8 it would be one of the two cylinders in the back by the firewall...not sure which side. If you are lucky it may be a loose plug wire or bad spark plug. Next you may want to test compression to see if it is a valve or piston problem. I hope it is something simple. Usually it is.
Hopefully it's not a valve seat come loose in the head. Hornet has the correct procedures for the process of elimination. But, in the 4.7 this is not a good trend. I'm guessing the mileage is very high too. The 4.7 hates to be overheated. Also noted for lifter problems at high mileage. They are prone to rolling a rocker out from under the cam at high mileage. Especially for those out there that only change their oil every 7 thousand miles. And then throw in the timing chains. If your at 150 thousand there wasted. Actually not the chains, but the guides and the hydraulic tensioners. Just eliminate things and eventually you'll find the problem. Head gaskets are a big deal on this engine too. If you can do the work yourself your good. If not be prepared to send your life's savings. Hope it works out for you.
