Spark Knock

['80RegalT-type]

I have what i believe is spark knock. The sound is a metalic knocking scratching kind of sound. It only happens when the car is started, when i put it in gear or when i run over a pothole or bump. The motor is out of an 80 sport coupe and I rebuilt it stock except with forged pistons and a slightly larger cam. I have zero low end power. The car won't break 1000 rpms going uphill but when i get her on flat everything goes fine once i get up to 20 mph or so. I don't have a pevc valve in at the moment. My stock one is shot and i'm in the process of rigging in a new one. Please help.

 

[b4black]

What your describing doesn't seem like knocking. Knocking is more of a "pinging" than a scratching. I might be worth getting a mechanics stethoscope (~$5) and listening around your idleing egine for anthing out of the ordinary (like the smog pump bearings).


No PECV will cause problems. Without vacuum holding the power vlave shut, the carb will be very rich all the time. Maybe a line from the power valve port on the carb to the intake, with a check valve to stop boost would work temporarily.

 

[Peter]

Just curious! Where did you find a new PECV?

 

['80RegalT-type]

As for the PECV, i've been looking in some japanese cars at the yard for a vacuum switch as described on petes buick web page. But no luck. Not 100% sure at what i'm looking at.

I have ruled out spark knock as the sound i'm hearing. I bought a stethescope and listened around but i'm still not sure. I bought forged pistons for the car and they look different from the originals. I read something about when they first made the motors and how they were having problems with the piston grabbing the pin so they added weight and an oil drip hole. Not sure if that's it. Hope not.

 

[Ttype83]

I'm starting to wonder know if it's not piston slap that you are hearing.
Does anyone remeber the thread about pistons? I remeber that some pistons had problems with this.
Jim

 

['80RegalT-type]

Piston slap!? I'm not sure what that is but it doesn't sound good. The sound has something to do with the motor being, atleast, slightyly josseled. Like when it goes into gear, I hit a bump in the road. I don't hear it at higher rpm's either.

 

[Peter]

Originally posted by '80RegalT-type
As for the PECV, i've been looking in some japanese cars at the yard for a vacuum switch as described on petes buick web page. But no luck. Not 100% sure at what i'm looking at.
.

I think this vac. switch was used on many early EGR cars both Japanese and domestic. It was probably used to control the EGR under temperature condions, and was operated from a temp. sensor. Later this was combined into one unit.

 

[Ttype83]

Originally posted by '80RegalT-type
Piston slap!? I'm not sure what that is but it doesn't sound good. The sound has something to do with the motor being, atleast, slightyly josseled. Like when it goes into gear, I hit a bump in the road. I don't hear it at higher rpm's either.

Don't get scared yet......
Mine has a rattle when hits bumps & stuff, sounds like a loose front end part. I have checked the front end,tie rods shocks...etc
but have not been able to find it. my 66 Rustang had the same noise.
First you need to find out more on the noise, have a friend run the rpm's up to 1800 or so and listin with the scope and see if you can hear any odd noises.
Use a funnell & 3 foot hose to hear noises around the engine it self, but the funnel to your ear and use the hose end to move around.
HTH
Jim