I have consistently been getting a P0306 misfire code for the past few months. I decided to take it to the Chevy dealership last week to have diagnostics run. They determined low (about 50%) compression in cylinder #6. I waved off further diagnostics - i.e., going into the motor - as I wanted to take some time to decide on my next move.

Chevy is recommending replacement of the engine based on the compression loss and some leaks they saw around the engine. I have been driving it since 11,000 miles, and I drive easy, it has never overheated, and I keep up on the maintenance. To anyone besides me or a mechanic, they don't notice anything wrong, but I can feel the slight misfire, and to me, it has been driving even a little more roughly in the past month. This morning, for the first time, the SES light was flashing just sitting in idle in my driveway.

This year I have replaced the vacuum lines, MAF, EGR, and PCV. Throughout the year I have also had a garage put in a rebuilt starter, cap, rotor, plugs, wires, fuel pump, and ignition coil. Before the misfire codes started coming up this summer, the moves I made this year had the gas mileage back up to its original advertised number of 20-21 mpg highway, and the truck was running great. Over the past two years, I have had a rebuilt transmission put on and everything underneath involved with suspension, including torsion bars, leaf springs ball joints, shocks, etc. The exhaust is original, but got a clean bill of health from the best spot in town last month. The body is good, the interior is great, and everything works.

I would like to keep going with this truck, as it is starting to turn into a new vehicle again. I am wondering two things: 1) is there something else that could be leading to that compression loss and 2) is it going to be worth it to put in a rebuilt or new motor, or even to look inside the engine and perhaps fix it?

I welcome any advice or ideas that the forum offers. Thank you for your time.

 

Well, first off shops are trying to make money so dont always believe what they say you HAVE to do.

Bad compression could be any number of things. Bad piston rings, bad head gasket, or burnt valve. If you aren't losing oil or coolant then i would say it has to do with the valve, which definitely doesnt require a new engine. You do have a lot of miles on it, and the original gaskets dont last long so it could be the HG as well. So I would look at your oil and see if its milky. If its not then there is a kit you can get to test the radiator fluid to see if it has exhaust gasses in the coolant.

And a flashing SES light means there is a potentially engine damaging misfire, usually means there is more than one cylinder misfiring. So go down to an auto parts shop and borrow their code reader (most do it for free) Plug it into the port on the left under side of the dash and get the codes. Then tell us what they are and we can help from there.

 

I appreciate your thoughts. To answer a couple of your questions, it is still showing up P0306 on the code check. The engine uses about a quart or less per month -- always shows up on the dipstick. No visible smoke from the exhaust. Also, there is no milky residue in the oil. I will try the antifreeze check.

 

You made a smart move by waiving off any more dianostic from the stealership.

To do a compression check is not difficult but a little time consuming providing that you have some mechanical skills.Buy a compression tester they are under $20.Test the compression on each cylinder to make sure you only have 1 with compression loss.As mentioned a bad valve or burnt valve will cause compression loss but usualy 100% loss if its stuck open.Bad rings will cause probaly 30%-40% compression loss and you would be burning a significant amount of oil.Also check your sparkplugs a blown head gasket wil show up as a wet and or fouled sparkplug and will if your burning oil also.

 

i had a 85 a few years ago with the same cylinder bad. back passenger side? bought it from a friend who bought it from another friend and it was like that when they had it. i wheeled that truck for 3 years like that with no further problems other then it being slow. i did a intake on it and checked and adjusted all the rockers and everything was fine and moving, im guessing it had a cracked piston ring or something along those lines

so if you can live with it just drive it til it blows then put a new engine in it

 

Unfortunately, I have the exact same dilemma. I'm going to do a full top end on the motor, as everyone I've talked to said there's a 95% chance it's a burnt valve. The ethanol in today's gasoline is what's doing it, they say. So I figure at 148k miles, it's a good time to do the heads up fresh, change the intake gasket, thermostat, plane the heads and replace anything worn... the added compression (a few points at most) should perk up the motor.