I have a 1989 EF sedan with the stock d15b2 and a pgmfi intake swap from a ‘91 integra. Since I’ve owned the car, it’s made this knock sound under engine acceleration. Here’s what I’ve done to it, related or unrelated to the issue:

• Plugs
• valve lash
• Varying oil viscosities
• PCV valve
• throttle body gaskets
• IACV oring and clean out
• ignition timing
• swapped ECUs (same PM9 code)
• new exhaust system minus down pipe from header to flex pipe.
• various fuel octanes
• cant remember what else.

owner said it was rebuilt 2k miles before I bought it, and I’ve put 10k on it and it’s never gone away. It’s worst when cold and almost goes away after being driven hard and fully warmed up. Sounds a little like an exhaust leak or very consistent pinging. I’ve unplugged the plug wires one by one and revved it, and it knocked each time. I don’t think it’s a connecting rod bearing or piston slap, but I haven’t borescoped it to check out the cylinder walls.

my next move would be plug wires or replacing that down pipe despite it looking newer. I may also take off the accessory belts to se if it’s a ps or alternator noise. After that I’ll just drive it till it blows up I guess. Let me know if you have a guess.

here’s a link to the video, if I get it to work without google drive I’ll edit the post:

https://drive.google.com/file/d/1J9pCY8C-zcj_Izghc_73rzM8Xxfs_CsH/view?usp=drivesdk

 

Since it was said to have been rebuilt, I would double check the valve lash clearance.

 

I set the valve lash to spec from the origenal honda shop manual. It may be an exhaust leak; I've replaced everything but the down pipe including all gaskets adjacent to said pipe. The sound is low, so its either that or what fear to be bottom end noise.