hello guys, new to this forum and have read up alot on internet about what could and couldnt be the issue. recently drove to cali from boise truck ran great on way down and up i had one code 305 came on went away.. I did a tune up with autolight copper plugs( dont ask thats what they gave me ) wires cap and rotor, she ran great no codes all is well.. then i drove up to lewiston to pick up daughter as soon as it hit first grade service light came on and she ran like shiz!!! anyhow 5 hours later pull into drive way she has ruff idle still showing code 305, changed to iridum plugs MSD wires, new cap and rotor still no change! did a compression test on that cylinder 50lbs? doesnt seem right, how could she drive almost flawless for 1500 miles then do a tune up and drop a hole?

so ive heard fried valve, rings toast, injectors bad, ??? when i pull the plug its perfect i dont smell fuel on the plug at all. could the injector be the problem? i read here that the injector could wash the cylinder causing low compresssion? explain this please your help is greatly appreciated..! single dad only means of transportation for me and my 6 year old girl.

 

Add a tablespoon or so of oil to the cylinder, turn the engine over a few times then re check compression. If the compression comes back up to normal then it was washed. If it still has low compression then time for a new engine or rebuild.
Nothing else matters if the compression stays low

 

can you message me this please, if im understanding correctly (theres an add in most of your message) add oil to the cylinder and if compression goes up then its washed? and if not then its mechanical correct?

 

Take a socket extension with a rubber hammer with it running, tap on it the injector, see if that clears it up.

 

If it is a 5.7 he can not tap the injector as it is inside the intake.

I do not give hep in private messages but will gladly in open forum.

 

im going to retry the compression test in the morning, and then try the cylinder next to it making sure i have it installed correctly and just to see what it is again. I pulled plug its perfect doesnt even smell like fuel at all, and add some oil to see if the compression goes up or stays the same. im really hoping it is a faulty fuel injector, but im almost to the point of seeing how much GM would charge to diagnose and go from there. FRUSTRATED!!!!

 

When doing a compression test, the throttle should be wide open and of course ignition disabled. Would recommend doing all cylinders.

 

so i took my tahoe into the chevy dealership this morning, and had them diagnose the issue............. 75psi in number 5 cylinder, they cant say if its burn valve or rings, it would cost another 100 to figure that out at any case its $2000 to rebuild upper end( motors got 165000 on it, or 3000 for a new motor installed with 3yr 100k mile warrenty! new motor is way to go right !?

 

Get the new motor. You could spend the $2000 and the bottom end fails next week, month or year. Then it would be like throwing that 2k away as you would have to spend the 3k on top of it. The warranty on the new motor is worth it. We use dealer motors at work for that reason. If you have a engine problem all the way across the country you can pull into and GM dealer and its covered. At work we would never recommend rebuilding the top end at that mileage (just asking for trouble).