Mechanics

WHAT IS INJECTOR KNOCK?

1995 Buick Century

1995 Buick Century 6 cyl Front Wheel Drive Automatic 100K miles

My car wouldn't run for more than a few seconds. I took it to the shop and they said it was the fuel pump in my tank. I took it home and replaced it and it started and ran. I drove it around for 15 minutes and it drove fine. Then I drove it down a big hill and back up and it wouldn't reach 55mph going up the hill.

When I pulled back up to the house I could hear this loud knocking sound. On idling it sounded like a ticking that would fade into a knocking and back. I even heard a couple of squeals out of it.

It really sounded like something was very wrong so I pulled the valve covers but everything looked okay. Continued to run it and the valves all looked like they were running properly but the ticking/knocking was really bad. My neighbor said that a piece of a valve must have broken off. I compression tested all the cylinders and they were fine.

I need to mention that this sound was CLEARLY in the top of the engine. I tried to isolate with a hose and that didn't help, but I was trying to isolate it among the rocker arms & cylinders. Nothing, but if you took the hose away it sounded like it was right in front of your face, definitely not way down in the bottom of the engine.

I tore the heads off anyway and the pistons, cylinders and valves look like they're brand new.

Can an injector make that kind of noise?

edit: also found metal shavings in the oil, these are definitely new. It also would sputter out and die occasionally when I was trying to isolate the noise, and then more and more often right before I tore it apart.
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Lo0p
April 27, 2010.




Did you pull the timing cover? It is possible that it has lost the nylon on the cam gear and maybe jumped a tooth or two.

Factoryjack
Apr 27, 2010.
No I haven't. I'm a novice when it comes to engines, could you explain to me what might be happening and how it's making that noise?

I want to have some idea of what I'm looking for if I need to tear the bottom part of the engine apart.

Tiny
Lo0p
Apr 29, 2010.
The original cam timing gear is coated with nylon. Over time this nylon wears out or becomes brittle and breaks apart, causing slack in the chain. This can eventually jump time and not run at all, but can move a bit and cause running problems, backfiring and stalling. With the lack of power and the stalling, it may be an indicator. Without being able to hear the noise and form a hypothesis, it is just a suggestion. Can you attract the metal from the oil with a magnet, this would indicate if it is steel. Do you know much of the history of the vehicle, has it been run hard or neglected service? It could have spun a bearing on a connecting rod. This will be obvious on a teardown, with excessive play at a connecting rod big(crank) end, and the bearing will be scored or remain on the crank. The coming and going of the knock may occur as the oil passage lines up at times.
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Factoryjack
May 6, 2010.

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