[vanillajackson]

Hi, I just recently fixed a vacuum leak that was causing a high idle. Now it idles good for the most part, but has a knocking sound from the exhaust. I don't hear it up front at all, or near the transmission, only from the pipe. What would cause this? Thought it might be the exhaust pipe hitting something underneath, but it's not.

The motor was recently rebuilt .020 over with low compression pistons, motor is stock otherwise. I haven't got around to fixing the exhaust pipe yet, so it's straight piped for now, loud, and full of leaks. I'm not sure if I would even hear it if I had a muffler. But it is pretty pronounced to me.

I don't think it's rod knock. I've got decent oil pressure according to the stock gauge, stays in the middle, maybe a little above when the RPMs are up, goes down to about a 3rd on the gauge when idling, and every other car I've heard with rod knock, you could hear pretty well in the engine bay, and usually got worse when revved up. This sound goes away when revved up. I mean I could be wrong I guess, hoping not though...

I should mention I just re-adjusted the timing. It was now showing to be at 15 degrees btdc, since I originally timed the motor to 10 degrees btdc with the high idle. But not sure if the sound started before or after because I checked and adjusted the timing before walking around to the back of the car. I would think retarding the timing would make a knock sound go away though, not make it show up. I set it following the TSRM.

edit I just remembered, I had the block and head milled, .005 of the block, and .002 off the head. Could that affect my timing enough to cause this?

I'm also running 87 gas, I saw a couple posts suggesting 92 gas. Was wondering what you guys thought about that.

I'm including a video to show the sound. Excuse my messy backwoods garage, it's also a work in progress.

 

[ItzCapt]

Definitely try 92 when changing your timing atleast from what i’ve heard is it will cause knocking if you don’t and i think you should make more power to

 

[vanillajackson]

I'll give it a shot this weekend. I have a CEL so I read the codes and I get 41 and 52. 41 is for the tps, and 52 is the knock sensor.

My car is an 83. It seems like I read the 82-83 didn't have a knock sensor. But I definitely have one, if that's what that is under the exhaust manifold.

Would a misaligned or bad TPS cause this?

 

[RedP85]

Under exh manifold is the Oxygen sensor. Knock was on 85+. Knock sensor is under intake runners.
May be interesting to know p/n of the ECU to ensure it's an 83. (above glove box).

 

[vanillajackson]

Ohh ok, the oil pressure sender is what I thought was the knock sensor. But yeah, no sensor under the intake.

I bet you're right though, it's probably an 84+ ECU. That would explain the tps too really. Since they're different.

The guy I bought the car from was using an 84 as a parts car. And I noticed on the extra intake manifold he gave me, the throttle body has a round style tps while mine is square. He probably swapped the ECU too. I'll pull it out and take a look. Thanks for the help.

 

[vanillajackson]

So I pulled the ecu and the sticker has been peeled off. The only number I see that could possibly identify it is on the pcb inside. It's 175031-0281.. which turns up nothing when searched.