Michael Moore. GM MASTER/WORLD CLASS. ASE MASTER replied 1 year ago.
You may have a bad lifter, camshaft or a broken valve spring. Because of the mileage, most techs would prefer to replace the motor rather then repair it. Unless you have a broken valve spring (which is easy to repair) I would also recommend engine replacement. You do not have to get a new motor, in most areas you can get a good used motor with low mileage at a very good price. I have heard them as low as $750 but you need to check around. The reason you do not want to repair this engine if it needs lifters or a camshaft, it will cost you more to repair this motor then it would to put a good used one in. You are looking at around $3k to repair this motor and you will still have 185k miles on it.
If you have a lifter that has stopped working, you can tell by running the engine with valve cover off and watching the rockers to see if one is not moving. Here is some more information on how to diagnose the engine noise from GM:
The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.
Some customers may complain of a SES light, engine misfire, and/or engine noise. If the SES light is on, the technician will find a P0300-P0308 DTC with misfires counting on a single cylinder that may or may not be felt. This may occur consistently, or it may occur intermittently. If a noise is verified, it will not be eliminated by canceling fuel injectors and the noise will occur at camshaft speed (half of crankshaft speed). The noise may be described as a chirp, squeak, squeal, or tick noise and may increase off of idle.
In either case, the cause of this concern may not be isolated after following SI diagnosis. This PI is written for technicians who experience this concern and follow SI diagnosis without isolating the cause of this concern.
If SI diagnosis does not isolate the cause of this concern, it may be the result of any of the following:
- Worn camshaft lobe and/or lifter roller
- A sticking valve
- Valve leakage
- A broken valve spring
- A collapsed AFM (Active Fuel Management) lifter
If SI diagnosis does not isolate the cause of this concern, review the information below, determine which description best matches the vehicle you are working on, and perform the suggestions as necessary, starting with the easiest ones first:
- Worn Cam Lobe and/or Lifter Roller:
Generally, a worn cam lobe on this engine family will create a consistent chirp, squeak, squeal, or tick noise at camshaft speed and/or a misfire with a P0300-P0308 DTC. The misfire may or may not be felt and the misfire could occur at all RPM or just a specific RPM, such as idle only or only at high RPM. If a noise is present, it will not be eliminated by cancelling fuel injectors and generally, the static compression and cylinder leakage will be similar on all cylinders.
The following suggestions may help determine if a worn cam lobe and/or lifter is causing this concern:
- Use a wooden hammer handle to apply pressure to the following locations of the rocker arms during the noise to determine which one is making noise: valve side, push rod side, and side of the rocker. If the noise is changed by applying pressure to the valve side of the rocker, this is most likely the result of a lifter and/or cam lobe concern on that cylinder. Sometimes this works, sometimes it does not - it seems to depend on the amount of cam lobe wear.
- Disconnect the coils and injectors on one bank of the engine, run the engine with the related valve cover removed, and back off the related rocker arm a couple of turns and listen for a change in the noise. If necessary, both rockers and push rods can also be removed one cylinder at a time with the related coil and injectors disconnected. If the noise is eliminated and there is no problem found with the valve spring, push rod, or rocker arm, this is most likely the result of a worn lifter roller and/or cam lobe.
- Measure the cam lobe lift at the push rod side of the rocker arm. The lift in this location will differ from the SI specification but it should be similar as compared with other rockers on the same bank. The misfiring/ticking cylinder should obviously have less lift than the comparison cylinders if this is the result of a worn lifter roller and/or cam lobe. Another
possibility of no/low lift on cylinders 1, 4, 6, or 7 on an AFM engine would be a collapsed AFM lifter. If a collapsed AFM lifter is found, refer to the latest version of PIP4568 for additional information.
- On engines with AFM (active fuel management), you can command AFM on with the scan tool, which will unlatch the lifters on cylinders 1, 4, 6, and 7 and stop opening the related valves. If the noise is eliminated, there is a good chance that the noise is coming from the valvetrain of cylinders 1, 4, 6, or 7. If there is no problem found with the push rods, rockers, or valve springs, the noise is most likely coming from a worn lifter roller and/or cam lobe on cylinders 1, 4, 6, or 7.
- If the tests above do not isolate the cause of this concern, it may be necessary to visually inspect the lifter rollers and cam lobes for obvious damage, such as flat spots, pits, grooves, scoring, gouging, flaking, rusting, etc. It is very easy to overlook a damaged cam lobe when inspecting them through the lifter bores and just because the lifter rollers are not worn, does not mean that the related cam lobes are okay. Both pieces need to be carefully inspected. It may help to use a bore scope or pen light when inspecting the cam lobes through the lifter bores. In some cases, the worn cam lobe may not be discovered until the camshaft is physically removed from the engine and inspected for the issues mentioned above.
Notice: Follow SI procedures to replace the camshaft and all lifters if a worn camshaft lobe or lifter roller is found. Also replace the plastic lifter guide for the lifter that had the damaged cam lobe and/or lifter roller (For 2010 Model Year, replace all of the plastic lifter guides). On AFM engines, also replace the VLOM (Valve Lifter Oil Manifold) filter screen that is under the oil pressure sensor.
Generally, a sticking valve on this engine family will cause an engine misfire that may or may not be felt and it may occur consistently or intermittently. It is unlikely that any engine noise will be present. It may be temperature sensitive and it may be more apparent during certain operating conditions, such as driving up a grade, cresting a hill, or during hard acceleration. A good indicator of a sticking valve is if engine misfires continue to count on an aggressive deceleration with engine braking. If the misfire occurs consistently, a static compression test, running compression test or cylinder leakage test may isolate the sticking valve. However, it is unlikely that any of these tests will isolate the sticking valve if the misfire only occurs while driving at specific conditions.
The following suggestions may help determine if a sticking valve is causing this concern:
Follow SI procedures to remove the valve springs and seals from the valves of the misfiring cylinder. Before removing the air pressure from the cylinder, tightly wrap a rubber band or tie strap around the tip of each valve stem to prevent the valves from dropping into the cylinder. Release the air pressure from the cylinder and work the valve up and down in the guide while turning the valve 360 degrees.
If any binding is felt, a stem to guide clearance concern exists and should be repaired by following SI procedures.
Notice: Refer to the latest version of PIP4753 for decarboning instructions.
Generally, valve leakage on this engine family will cause a consistent engine misfire that may or may not be felt and is more apparent at idle or low RPM. Normally, no engine noise will be present and in most cases, a static compression test or running compression test will not reveal anything abnormal unless the leakage is very high.
Notice: If a valve sealing concern is found, it should be repaired by following SI repair procedures.
Generally, a broken valve spring on this engine family will cause a tick noise and/or an engine misfire. In either case, the concern may occur consistently or intermittently. If it is causing an engine misfire, it may or may not be felt and it may only occur at specific operating conditions, such as high RPM driving, etc.
Notice: If a broken valve spring is found, replace the broken valve spring as necessary.
Some customers may comment on an SES light, engine misfire, and/or tick noise. This may be the result of an AFM lifter that unlocks as soon as the engine is started or one that is mechanically collapsed/stuck.