'89 325is. >300K miles (est), semi-daily driver.
Had the car about 6 years.
Cylinder 5 exhaust valve ended up getting some carbon deposit build up on the valve land and lost compression (62 psi compression). Drove it into the driveway on 5 cylinders (ran really good, all things considered). Removed the head and everything attached to it as necessary. Cylinder walls are super clean. Pistons looked really good. I pulled a replacement valve from a donor head that had a damaged distributor boss, lapped it in, and reassembled with all new gaskets & seals.
Compression on all 6 is between 120 & 125 psi
I have verified that I have spark on all 6.
Timing was set crank to block notch, then verified on harmonic balancer after a couple revolutions. Checked again via TDC on balancer with valve cover off and by wiggling the cyl #1 rockers to verify they’re off the cam.
I am getting fuel from the injectors, though I have yet to pull the rail.
I have spark via brand new plugs gapped to 30.
CPS and Cam Sensor resistance read within specs. CPS was untouched throughout this process. Plug wires are correctly connected at distributor (I’ve re-checked a thousand times).
Will NOT start. Will not even try to start. When I’m turning it over, it periodically slows the starter and/or hisses into the intake as if it’s trying to start backward. I’ve tried spraying starting fluid into the tube just downstream of the ICV, and it definitely puffs back into the intake, making the throttle body snorkel briefly expand a little. When I give up trying to start it, the intake manifold will even feel slightly warm, and the exhaust will feel stone cold.
I’ve run out of things to check. The regular boards are clueless. Hoping the more hands-on racing community can help. I suspect I’m missing something obvious. Please advise!