[Quadzilla724]

I have a 2002 Trailblazer (4.2L 102K miles) and about 6 months ago wrote about an idle problem that has since been fixed. The tech noted a 'rattle' in the engine at around 2K RPM. I had observed this myself, but didn't say anything to them about it. Now it seems worse. It starts this at 1,500 RPM when accelerating. The harder the acceleration, the louder it is.

I looked up Piston Slap and the noises described sounds exactly like my problem. There was even a sound clip to listen. It rattles, gurgles, and sounds like a diesel engine. However, everywhere I read on this, it stated that it begins right at start-up and stops when the engine warms up because the pistons expand when warm. Mine is the opposite. It doesn't do this when cold, but starts once the engine warms up. Would this rule out Piston Slap or is this still possible? Should I consider a more serious problem?

BTW, I had a Cavalier years ago that did this and was confirmed Piston Slap by a tech. He told me there really wasn't much I could do about it short of rebuilding the engine and it really was more of an annoyance than an engine problem.

Thanks for any insight.

This post has been edited by Quadzilla724: 25 April 2009 - 02:27 PM

[TECH II]

I doubt it's piston slap......it starts on a cold engine, and goes away as it warms up.....

Cold engine has thick oil......as it warms, the oil gets thinner, causing clearance tolerances to increase, causing a knock...is it in the lower or upper end?

Possibility is a cracked cylinder liner.....

[smj999smj]

Could also be an issue with the variable camshaft timing system. Had one the other week that was making some noise and found the cam position actuator was leaking really bad, located on the passenger side of the engine, in the head. Have to remove the P/S pump to replace due to its length.

[kev2]

piston slap, cam actuators, wrist pin all pretty serious and pricie...

before we have you burning it for the insurance money try to isolate it, upper- lower- valve train- ign knock- the engine is not setting a knock sensor code? ...

> So lets think positive...
Could it be spark knock a crrboned up comb chamber (cc), run some top end cleaner /CC cleaner. 15$
> A lifter not oiling- try a detergent in oil ie "risoline" 5$
> then hoping its not mechinical change oil to get rid of those add a
qt of lucas oil treatment at the oil change- that might quiet it down and give us direction.... 10$

[Quadzilla724]

OK, thank you. I will post back. Much appreciated to all.

Edit: I am getting intermittent 'check engine' light. Mostly off...comes on for a small period (one or two drives), then goes back out for a couple days. Very inconsistent. But the noise is constant except for the first 1 or 2 minutes of driving until the vehicle is warmed up.

This post has been edited by Quadzilla724: 26 April 2009 - 08:42 AM

[kev2]

if there is a light there is a code....some auto parts stores will read them for free as a customer service let us know

[smj999smj]

This is worth looking into:

[smj999smj]

Also worth noting:

File in Section: 06 - Engine/Propulsion System

Bulletin No.: 02-06-01-032

Date: October, 2002

TECHNICAL

Subject:
Exhaust Noise/Leak
(Replace Exhaust Manifold Fasteners and Gasket)

Models:
2002 Chevrolet TrailBlazer
2002 GMC Envoy
2002 Oldsmobile Bravada
with 4.2L Engine (VIN S - RPO LL8) and Automatic Transmission (RPO M30) Built from Start of Production to January, 2002

Condition

Some customers may comment on an exhaust noise or exhaust leak. The noise will appear to come from the area of the exhaust manifold.

Cause

The fasteners used to hold the exhaust manifold may have relaxed and lost clamping power. The manifold will then be allowed to move under certain conditions causing a small leak.

Correction

Install a new exhaust manifold gasket and fasteners. Use the part numbers listed below.

The new fasteners have the proper adhesive in patch form already on the threads. DO NOT use any additional thread lock material.

1. Remove the exhaust manifold fasteners and gasket and dispose of properly.

2. Make sure the manifold bolt holes in the cylinder head are clean of debris or foreign material.

3. Install a new exhaust manifold gasket.

4. Install the exhaust manifold using new fasteners.








5. Tighten all fasteners in sequence to 20 N.m (15 lb ft).

6. Tighten each fastener a second time with the same sequence and torque.

7. Tighten each fastener a third time with the same sequence and torque.

[gmctech2000]

i would look at the exhaust leak possibilty more so, have seen a whole lot of them...quite common, and it could turn on the ses light....

[Quadzilla724]

Thanks for the bulletin. Unfortunately, my TB has 102,000 miles on it. As for the exhaust leak, would it cause a knocking sound?

Incidentally, I mentioned it knocks when RPM is over 1,500. But the other day, I could hear it while it was idling (I was standing outside the car).

[TECH II]

Pull plug and then squirt couple drops of oil into the cylinder...plug back ....start vehicle....the exhaust will smoke for awhile....if there is a leak you will see it...