M20 stroker misfire. Detonation?

[jimrat]

Hi

I’m having problems with a persistent misfire on my engine (stroked 325i). The engine starts and idles fine, has plenty of power, but misfires when idling, hot or cold ”“ you can feel the car shake. There’s also a slight stumble when the throttle is opened. There is also a weird ”˜internal clanking’ sound sometimes when idling ”“ not rhythmic like a big end knock - I’ve posted a video on youtube ”“ I’m a bit worried it is detonation”¦

The engine is a ”˜standard’ stroker: eta 2.7 crank and rods; skimmed 325i block and pistons, with 325i head and ancillaries. The motronic ECU is running a ”˜stroker’ superchip, and there is a vernier timing pulley, set to 18 degrees BTDC for inlet valve 1 opening. The engine has done about 2000 miles since it was built, and as far as I can remember has always had this misfire.

When it was built it had new HT leads, coil, sparks, dizzy, rotor, temp sender etc. There are no vacuum leaks in the inlet manifold, throttle switch is working OK and I’ve gone through most if not all of the Bentley checks but cannot trace the fault. I’ve done a compression test and all cylinders are OK, plugs aren’t fouled, and I’m not having overheating problems.

Any suggestions? Could it be a timing issue? Can anyone recommend a specialist not too far from Bristol who could tune the car up? Is there any point taking it to a rolling road with this misfire?

Thanks
Jim

[E30coupwes]

Hi mate

I'm interested in the conversion you've done, I'm basicly doing the same but with an up rated cam. I'm guessing you've used high compression Pistons? How much have you had machined of the Pistons and how much have you had skimmed of the block?

Have you got it running now okay now?