Mechanics

HELP ME DIAGNOSE THIS SOUND

1992 Chevrolet Lumina • 68,000 miles

92 lumina makes clicking sound when accelerating, but not idling. Sound does not change pitch. It's a constant loud clicking sound while accelerating, but stops when I am not accelerating. Sound seems to be coming from bottom of car as I hear it best through the side windows.
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Blindsided
June 16, 2012.



This can be typical of an exhaust leak at the manifold. You might also be able to make the sound by doing a light "brake stand". Hold the brake on, then raise engine speed while in drive. If you hear the noise, you know it's not drive train-related because the car isn't moving.

Caradiodoc
Jun 16, 2012.
Sounds like its pinging-does it sound like a bunch of marbles being thrown into a tin can when you're accelerating

Rasmataz
Jun 16, 2012.
Caradiodoc-

I tried it. I shifted to drive, held foot firmly on brake and accelerated. The car made the noise. So, does that mean it's likely the exhaust manifold? If so, I bet that's a pain in the neck to replace myself. Thank you for your help!

Tiny
Blindsided
Jun 16, 2012.
You don't typically replace anything except in the rare event it's cracked. Usually it's tighten some bolts, replace a steel gasket, or repair some other leak in the exhaust system. All depends on the cause of the noise.

Rasmataz suggested another possibility with spark knock. That would also only occur during acceleration. The best approach is to have a mechanic listen to the noise and perform an inspection.

Caradiodoc
Jun 17, 2012.
Caradiodoc- Thanks so much for your advice. A mechanic would be the wise choice, but my income does not permit it (that's why I own a 92 lumina-lol). Anyway.I have one point to bring up. If it were the exhaust manifold. Wouldn't it make the sound while in park? When I am in Park, and hit the gas. It makes no sound. It's only when moving. And also in your suggested brake test.

Tiny
Blindsided
Jun 17, 2012.
Usually it has to be under load for exhaust systems to make a noise. It can be due to increased pressure in the system, the engine is rocking and exposing a leak in the spring-loaded flexible connector, or just because more power comes from more burning fuel and the noise gets louder.

You can also use a helper to make the noise, then listen under the hood with a stethoscope. You can find them at any auto parts store for less than ten bucks.

Caradiodoc
Jun 17, 2012.
It does make sense, however. In park.I can jam my foot to the floor and ZERO noise (I checked with a helper). However. In Drive or reverse. It sounds like a train like choo choo when accelerating (even when not moving. Like your brake test showed). Actually, I sort of hope it is the exhaust manifold, as this is not as bad as some other problems. Furthermore, I will not have to fix immediately if it is.

Tiny
Blindsided
Jun 17, 2012.
Besides the noise, there actually is a way a leak can cause problems. Between the pulses of exhaust gas flow, the momentum creates little pulses of vacuum that can draw in outside air through that leak. The oxygen in that air will be detected by the oxygen sensor as a too lean condition. In response, the Engine Computer will request more fuel to go with that air. No matter how much extra fuel it requests, there will still be that unburned oxygen so the computer will keep asking for more and more fuel. The mixture going into the engine will be way too rich, you might smell raw fuel at the tail pipe, but the computer will think the mixture is too lean and it has lost control.

Most of the time that doesn't happen and the engine runs fine. This is one of those scenarios that are the one out of a hundred cars that no mechanic can figure out.

Caradiodoc
Jun 17, 2012.