Tonight after washing and waxing my 85 Z28 and putting the panels back in, I took it for a spin to put some air in the tires. I stopped by work to see how things were going away from home, then pulled into the gas station. After I got all my tires to 40 PSI, away I went back home. But on the way I noticed something rather strange. I gave it some gas on a straightaway and I heard a faint rattling/knocking sound. At first I figured it to a window or panel inside the car as they usually do, but this one sounded different. I immediately backed off the throttle and rolled down my window. I gave it some gas again and heard a foomping sound from my exhaust. I pulled into an empty parking lot and put it in neutral and began revving the engine. Whenever I gave it a sudden rev, I would hear the noise again.

I popped the hood and reached for the throttle body and gave it a sudden increase in throttle. I heard a definitive knocking noise coming from the engine. I revved it again a tad harder and this time it was worse, and almost sounded like it was coming from the drivers side, but then again hard to tell if it was coming from the passengers side too.

What in the world could this be? Is it possibly something I can fix myself? This car is my only means of transportation and I can't afford another repair bill right now. Something else important is that the knock only occurs when you give a sudden rev or increase in throttle. It does nor occur whatsoever at idle and is either non-present or too faint to hear when you are very delicate with increasing the throttle. RPM level does not seem to have a play in this, although right now I am afraid to rev above 3500.

One other thing. Could octane level play a role in this? About 2 days ago I started regularly using 93 because I found out my ECM has a JET Performance (Don't worry I plan on going back to stock very soon) stage 2 chip in it and the JET website says 91 octane must be used (around here it goes from 89 to 93, unless I drive down to the nearest wawa where they have 92). I regularly used 89 with no apparent problems, but I have used 93 before and don't recall this ever happening.

 

I just took the car up to 7-11. With the windows down the noise is now more characteristic of a pop than a knock.


Same story otherwise. Baby (And I mean just popped out with the umbilical cord still attached) the throttle and no noise whatsoever. Put the car in neutral and slowly got it to about 3200 RPM without anything odd.

What is going on here!?

 

Well, if it is something this intermittent, I doubt that it is an internal engine problem. Make sure your oil pressure is good and oil level is good, and antifreeze level is good, basically all of the basics. The other thing to check is that all all of your exhaust manifold bolts are there. You may have lost one and when the engine is cold it could be leaking more exhaust than when the engine is hot.
Check to make sure that all your plug wires are nicely connected. Also make sure that there aren't any parts of your exhaust that are tattling.
How does your car drive? Does it seem to have less power?
Give it a good look around and see if you can hear the noise again and locate where it is coming from.

 

Could be a loose flexplate or torque converter bolt, or it could be a rod bearing.

 

Well, thanks for the input guys, but my engine is toast. It's much worse now. You can hear it at idle now when the engine is warmed up and I'm afraid to give it sufficient enough throttle to hit second gear.

I took it to the shop and they said it sounds like a rod is taking a dump. It's also backfiring through the intake. A guy at the junkyard said it sounds like a bottom end knock and that the rod will be coming through the oil pan REAL soon.

So for now since I can't afford a full 350 swap I'm gonna gnab another 305 for $705 and get someone to help me drop it in. Unfortunately, I don't have the expertise it takes to rip the engine apart and replace the busted parts myself, and if I had the shop do it it would be wise to overhaul the 7 other cylinders while they were at it which would probably cost more than a new engine.

So, time for another 8 banger.

 

I had to go through the same thing just 3 months ago. It is a sad situation. However, I think that you might be able to pick up a decent running 305 for less than $700. Good luck.

 

What about a 327? I heard that was a drop n go sort of deal?

 

Any smallblock chevy is drop and go, but the different headsa nd displacements are goig to cause problesm with the fuel injection.

Your best bet is to scour the classifieds for the exact engine you have that was pulled out of a running car. Whether it's an LB9 or a LG4 or whatever. You can find running 305s for less than $200 all day long.

 

if its backfiring the cam is most likely shot, the metal is probably circulated all over the motor.