Loss of power, tapping noise

ZEROGHOST

MEMBER
2000 CHEVROLET SILVERADO
V8
2WD
AUTOMATIC
136,000 MILES

My truck listed above is a 3500. Just bought this truck a few weeks ago. It needed a new exhaust manifold when I took it to be checked out.

I had it replaced then less than a day later the check engine light came on. The code told me it needed a new o2 sensor. I took it to the mechanic and hes telling me it was the crankshaft sensor which they swapped out and said it did not fix the lack of power.

They then did a leak down test and said that was fine as well.

He believes the tapping is a valve issue but cannot tell me anything else. He says I just need a new engine.

I have rebuilt several motorcycle engines and usually do all of my own work. I have never swapped a truck engine, but I do not think I want someone who cannot even tell me the cause of the problem doing it either.

Anyone have any good ideas or common issues with this vehicle to give me a start before an engine swap?

3 Replies

CARADIODOC

MECHANIC
33,873 POSTS

Before you get wrapped around the axle difficult stuff, at the mileage you listed, consider a stretched timing chain that is slapping against the housing. GM engines are well-known to have knock sensors pick up knocks that are not spark-knock-related. The engine computer retards spark in response to what it thinks is spark knock. That retarded timing results in low power and poor fuel mileage.

You can also view ignition timing on a scanner to see if the engine computer is constantly keeping it retarded.

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Monday, November 27th, 2017 AT 7:59 PM

STEVE W.

MECHANIC
13,476 POSTS

I would also grab a mechanics stethoscope and have a listen all around the engine, you can pinpoint where the noise is coming from and get a better idea of the problem.
A simple compression and leak down test would also tell you a lot. I would do a bunch of testing before doing a swap only to discover it was a timing chain or bad rocker arm.

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Monday, November 27th, 2017 AT 9:38 PM

PATENTED_REPAIR_PRO

MECHANIC
1,853 POSTS

The tapping noise is because of the excess lash or space within the valve train. It could be because of a worn down camshaft lobe, a collapsed lifter, a worn or bent push rod, a rocker arm stud that has pulled out of the cylinder head or even a valve that is not seating all the way because of carbon buildup on the valve stem.
None of these mean that you would have to replace the entire engine. The first thing you should do is remove the valve covers and see if there is anything obvious that you can see with the valve train.

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Tuesday, November 28th, 2017 AT 6:32 AM