I just got the engine running and now I have a knock! Please help!

[Wingnut87]

You guys were so helpful in my last thread. I found a fuel problem right away and fixed it promptly. I had sucessfull test drives until today when I gave the car some throttle for the first time getting on the highway. Since then I have had an engine knock. I hear it at idle faintly. Then it goes away if I rev it until about 3000 when it comes back louder. the sound comes from the front or passenger side of the engine. It happens regardless of clutch, so I don't suspect the trans. It still happens with the serpentine belt off so it is not an accessory. Naturally I have not been driving it and am afraid to run the engine now.

I'm attaching a log file I took when I was listening to the engine. Is there anything I should check first? I can't believe the problems I've been having with this project, but the last thing I expected was to tear down the engine. Is there anything it can be besides a mechanical failure?:frown:

thanks,
Tom

[Wingnut87]

Here is the log file.

[joecar]

Could you be hearing the infamous piston slap...?
I believe quite a few LS1's assembled before 2002/2003 had this.
Most noticeable from passenger side.
Can be pretty loud on some, not so loud on others.
Goes away under load.
Are you sure it's not valvetrain noise...?
Are you sure the motor mounts are not loose...?
Are you sure nothing is loose or banging...?
Do you have a stethoscope $20 from Sears (or make your own with some vinyl tube and a sawnoff screwdriver)...?

[Wingnut87]

So I made a stethoscope and was listening around. The knocking is loudest when I touch the water pump housing close to the outlets for the heater. I have these blocked off. It still happens when I remove the belt, which leads me to believe it isn't the pump, I'm just transfering the noise through it. I don't hear much on the valve covers, head, or exhaust ports.

The noise happens at idle and up around 2500rpm or so. Sometimes it goes away at idle, but comes back if I rev the engine. I doesn't seem temperature dependant. I've been doing some reading on piston slap (an engineer friend listened to it and thought that is what it was). It seems GM's opinion is to ignore it and it will not do much damage. Other people have their engines rebuilt. Many people only have the noise for a few minutes during warmup. This is not my case.

Is there any way to know for sure if it is piston slap? Should I keep driving the car or start tearing the engine down?

Man, this is the never ending project. I have 80 miles on the car in the last year. I also don't have thousands to spend. Only a hundred or two here or there.

thanks,
Tom

[Wingnut87]

Also, I checked the fuel pressure and it was 52psi. I know this is low and will correct it right away, but I did drive it for two days at that pressure. There is also and oil leak between the engine and trans (engine oil, not trans oil comes out). It is slow enough that it takes a few months to loose half a quart. I filled tha tank just before the problem, but it was I don't suspect bad gas from station (it is a new and busy station).

Anyway, you can never have too much info.

thanks again,
Tom

[emarkay]

For starters, check the oil pump, OP pressure relief valve, cam bearing, timing chain, a bad lifter, bent pushrod, or a "Murphy Gremlin"; a cable tie, a piece of sheet metal, or a loose doohickey that is vibrating or otherwise making an unwanted noise that is transferred through the block... :)

[Wingnut87]

I've been reading through alldata and have not found much information on the sensor. I know there is one on the driver side behind the intake manifold. It is refered to as the "pressure switch," "pressure sensor," and "pressure sender" and I'm under the impression the PCM uses it to disable the fuel pump if the engine is not running. EFilive will not log it. So I'm going to put my meter on it and measure the voltage. Or disconnect it and measure the ohms. Does this sound like the right thing to do?

[Wingnut87]

Oops, I posted the last reply to the wrong thread.

sorry