Knocking/pinging/detonation?

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krakrak

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Hi,

I posted on the j-body forum but got no response, so I'll try it here (but rest assured that if I find the fix I'll post it in the other thread, just to be nice!)

I need help from some 2.4L guru.

My car is a 1999 Sunfire GT convertible, with 153,000km (95000 miles), 4 speed auto.

It runs fine, no problem starting hot or cold, acceleration is great.

But when it's idling, if I give it a slight sudden push on the accelerator, I hear knocking. It's worse when the A/C is running. It will knock for half a second, just as the accelerator was pushed, and otherwise it never knocks (appart from when starting the engine, when the engine revs a little it does it once).

You can hear the knocking in this video:
https://www.youtube.com/watch?v=OgKiIDAUBus

Thanks!
 
the fact that it does it in park or when you start points to the sound not having anything to do with pinging or detonation, the engine has no load on it. You need to pinpoint the source of the noise. Using a length of rubber hose hold one end near you ear and move the other end around to various parts of the engine to determine the source of the noise, you obviously may need a second person to rev the engine while doing this.
 
does this car have a check engine light om?

The noise sounds like a stripped out gear or a belt slapping the timing cover.

I would start by pining down the noise like melsg5 suggested.

If you have any codes post them here.
 
EaOutlaw said:
does this car have a check engine light om?

The noise sounds like a stripped out gear or a belt slapping the timing cover.

I would start by pining down the noise like melsg5 suggested.

If you have any codes post them here.
Click to expand...


Yes the check engine was coming on sometimes. But I replaced the MAP vacuum hose which was broken and no check engine since then.

If it was a stripped gear or a belt slapping, it would do it all the time? Because appart from the first half a second when starting from a stop, the engine runs great, has lots of power, and doesn't make any strange noise up to redline.

I went to a local mechanic, and he said that I should change the spark plugs to genuine AC Delco before investigating further. He said that the 2.4L is fussy about plugs.

Thanks for the reply, I'll get back with the solution when I find it. If anyone else has a suggestion, I'm open for them.

I love great communities like these :D
______________________________
 
melsg5 said:
the fact that it does it in park or when you start points to the sound not having anything to do with pinging or detonation, the engine has no load on it. You need to pinpoint the source of the noise. Using a length of rubber hose hold one end near you ear and move the other end around to various parts of the engine to determine the source of the noise, you obviously may need a second person to rev the engine while doing this.
Click to expand...

I don't have a rubber hose, but I tried to pinpoint the sound using the old screwdriver on the ear trick. It was hard to locate, but the sound seems to come from the engine block or the head. I know for sure it doesn't come from the valve area, or the timing chain cover.

Thanks for the suggestion. :)
 
Did this mechanic actually hear the sound, because using non AC Delco spark plugs dont cause that kind of noise?
 
Check the front of the motor. Could be the Timing Chain Tensioner. This a common problem the the Quad motors.
 
Zimgxp said:
Check the front of the motor. Could be the Timing Chain Tensioner. This a common problem the the Quad motors.
Click to expand...

Yes, I'm beginning to suspect the timing chain. :(

Is it possible that the rattling sound when revving up is the loose timing chain rubbing on something?

Is it costly to replace the tensionner? Can it be done without removing the engine (is it accessible by the wheel well?)

Thanks!
______________________________
 
the job can be done without removing the engine. I recommend finding a shop with ASE certified mechanics. The cost is based on the hourly rate so shop around.
 
I found the problem.

While I was working on adjusting the a/c compressor clutch I removed the accessory belt.

I started the engine without the belt, and to my surprise the noise was gone. I then installed the belt and the noise was back.

It was clear that it was coming from either the alternator, the tensionner pulley or the compressor. It couln't be the compressor, because when the clutch is not engaged it doesn't even turn.

Having this info I was able to pinpoint the noise, and I'm positive (and my girlfriend concurred) that it was coming from the alternator.

I already ordered a new one, and will change it this week.

I'll also have to change the radiator fan motor, the engine temp was going up in traffic and I checked the fan and it doesn't work even with a/c on. Checked the relay (by swapping it with the heater blower) and it's good. I tried wacking the motor hard and it started, but when it's stopped it doesn't start up again.

And now I have a coolant leak from a hose behind the engine, just below the exhaust manifold.

I hope it's the last problem for a while, wish me luck!
 
Glad you found the problem and good luck with the car
 
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