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Mike S.
Mike S., Chevy Mechanic
Category: Chevy
Satisfied Customers: 7433
Experience:  ASE Certified Master Technician
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My question is about my 03 Silverado 2500hd crew cab auto

Customer Question

Hi. My names Noel and my question is about my 03 Silverado 2500hd crew cab auto 4x4 with the 6.0 LQ4. It has 220k and ran great until...
My "mechanic " started to do a crankshaft relearn because of random misfire on highway, none around town. Now apparently the first step of crank relearn is to hit the rev limiter at 4500rpm. My truck has a hypertech max energy programmer tune in it and I guess it removed the rev limiter so when the mechanic punched it, it over revved to 6000+ rpms. Now I have a ticking or tapping at idle and above 2000 rpm when under a load. It's actually gotten a bit better over the past few days. Actual mph makes no difference. If it's under a load or "pulling" at about half throttle or more, it taps. It also is a little louder the more gas I give it. I'm mechanically inclined and familiar with my truck but def not an expert. I'm sure we can figure it out together
Submitted: 9 months ago.
Category: Chevy
Expert:  Mike S. replied 9 months ago.

Hi, I am Mike, welcome. I'm reviewing your question.

Expert:  Mike S. replied 9 months ago.

A tap is usually excess lash in the valve train and a lifter tapping because of the extra space. What happened could have been either a collapsed lifter or a bent push rod.

Customer: replied 9 months ago.
Ok so would you say it's safe to say that it's not serious, as in piston to valve clearance, bent valve or rod knock?
Expert:  Mike S. replied 9 months ago.

What I would do is before adding some STP or straight 50 weight motor oil to see if it quiets down meaning it is mechanical try to determine which cylinder it is on first by canceling out each cylinder one at a time listening if killing any cylinder causes the noise to change, then remove that valve cover and watch as the engine idles if either of the 2 push rods on that cylinder wobble when they spin. Also you can take a piece of wood 2x4 and press on the side of the rocker while the engine is idling and if the noise changes that lifter is probably collapsed.

Expert:  Mike S. replied 9 months ago.

No, it is serious cause if the noise begins to get worse something could go really wrong depending on what it is, but like you said connecting rods usually knock when they go bad, I doubt if it's a bent valve cause if it were it would not seat and that would cause a misfire and I don't think piston would make that noise, only maybe a slap.

Customer: replied 9 months ago.
Ok. There's no misfires so it's not likely a bent valve, the characteristics of the noise don't resemble a rod knock. Is there any noticeable difference in a collapsed lifter or bent pushrod that would help me distinguish between the two before I pull the covers?
Expert:  Mike S. replied 9 months ago.

Other than like I said, I the push rod wobbles, remove it and roll it on a flat surface to double check if it's bent. Pushing on the side of the rocker may check if a collapsed lifter. I would kill the cylinders first to determine which one it is. If you have a scan tool, that might have a option in it for that, if not, there are several ways to do so, one being unhooked each fuel injector wiring is this has an injector on each cylinder. Another which I don't like to do is disconnect each coil on plug primary wires if it's COP.

Customer: replied 9 months ago.
Ok. Thanks
Expert:  Mike S. replied 9 months ago.

You are welcome, don't forget to rate me well if we are done here.