Knocking sound when accelerating

VDUBED2

MEMBER
TOYOTA PICKUP

Hi,
I have a 1994 Toyota Pickup 3.0L V6 4x4 with 175000 miles. I have recently replaced the head gasket after repairing a stripped out spark plug socket. During this process I decided to replace the timing belt as well. After everything was back together I started it up and noticed what sounded like a very faint knocking, similar to a diesel engine sound, coming from the area where the downpipe exits the engine bay. I have been driving it like this for about 900 miles and the sound is getting much worse, now increasing in volume whe I accelerate. The timing is dead on, 10 deg BTDC, however I am not sure if I replaced the valve lifters in their original positions. Could this be the problem? I have never acutually heard what an engine knock sounds like so I am not sure if this is it either. The knock seems cyclical, like it is happening every revolution, or maybe slower. I had the heads machined prior to instalation and I think it increased the compression. I was getting readings of 170-180 psi in all 6 cylinders. Do I now need to use a higher octane fuel?

Thanks,

Matt

3 Replies

RASMATAZ

MECHANIC
75,992 POSTS

I need to know what kind of noise-is it a ticking, tapping, thudding, thumping, or a bunch of marbles being drop into a tin can ( Detonation/Spark Knock)

BTW did you jump the diagnostic connector TE-1 to E-1 while adjusting the ignition timing. If not you need to do this to get it right.

HTH/Good Luck

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Tuesday, July 17th, 2007 AT 5:35 AM

VDUBED2

MEMBER
2 POSTS

Thanks for the quick response. The sound is more of a thudding than marbles in a can. It occurs only when the engine is under load or accelerating. If I rev the engine in neutral it dosen't occur, or it is at least so faint I can't hear it over the engine noise. I did jump the diognostic connector and the timing is dead on. My real worry is that I am doing mechanical damage to the internals. Is this a possibliliy, and what may cause it? Any more knowledge as to what it could be would be greatly appreciated.

Thanks,

Matt

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Tuesday, July 17th, 2007 AT 2:48 PM

RASMATAZ

MECHANIC
75,992 POSTS

It sounds more like detonation, it will damage the engine-

Possible causes: EGR, engine overheating, low octane fuel, high compression, lean A/F mixture, spark plug heat range/knock sensor.

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Tuesday, July 17th, 2007 AT 3:18 PM