whoever figures this out...100 bucks paypalled to them..

[bmwman91]

You only need to remove the valve cover to check.

If it was running properly, pulled out of the donor car and put straight into yours, then it probably is not the timing.

[MF DOOM]

are you sure all your sensors are plugged in correctly? No two are swapped?

[CHIF8008]

double check everything. again, dont just assume you have it right the first time

[FLG]

Spark plug wires on the correct cylinder?

http://blog.bavauto.com/wp-content/uploads/2012/03/M42-E30_Coil_Wire_Routing.jpg

[AlphaE]

Posted this in ur other thread as well. I may be crazy but sound like ur exhaust is plugged. Runs enough to build pressure, can't get rid of pressure, dies, pressure leaks back through intake and air filter. Need vid. What's this boom? Like backfire? Sound mechanically related not electrical. Cam timing is off. Exhaust valve hung up,exhaust system plugged. Something along those lines.

[timofeylbelarus]

i've had something like that too the car cranked but didn't start after i put everything together, came out to be i hooked up the coils the wrong way, when i put them the right way it fired right up

[lateralfx]

When I did my swap I had the same problem. Turns out I had the coil pack plugs backwards. As soon as I swapped it around it started right up. I felt pretty dumb to mix that up. Took a few hours to figure it out too. But it was a simple fix. My 1-2 were in 3-4 it was 180 off

[broach328]

yeah I was gonna say this ^ either you could have the coil packs/plug wires out of order, theres a mechanical issue with the cam timing, or possibly a tappet issue(valve is hanging, causing possible backfire when it dies out. I have experience a similar issue before and it was timing related. What happened was, it would start and sound very rich and hardly idle. If you opened the throttle body at all, it would die out and it made a large detonation into the intake manifold similar to how your describing. In my case, it was a 24v motor and it blew the ICV off the intake manifold and did no other damage. In your case, it might have blown the intake manifold gasket or cracked the manifold or maybe even no damage at all. First of all though, I would check that coil packs are all hooked up properly on both the engine wiring harness to coils and in order from coils to spark plug. If those are in order, I would then check the cam timing. If that isn't your problem, run a compression test to make sure valves, hg, etc are all operational. Get back with us after that but its more than likely one of those issues.

[wazzu70]

When I did my swap I had the same problem. Turns out I had the coil pack plugs backwards. As soon as I swapped it around it started right up. I felt pretty dumb to mix that up. Took a few hours to figure it out too. But it was a simple fix. My 1-2 were in 3-4 it was 180 off

This. Make sure the coils are plugged into the correct plug. If you get this mixed up the ignition timing will work, just at the wrong time. The bang at the end when turning the car off is an obvious sign.

I did this when swapping in my M42. Thought for sure I had them plugged in correctly, but I had two switched.

[broach328]

I did this when swapping in my M42. Thought for sure I had them plugged in correctly, but I had two switched.

Yeah, and those aren't numbered for some reason so you have to trial and error

[irish44j]

Yeah, and those aren't numbered for some reason so you have to trial and error

you can use a multimeter and measure resistance from the DME pinouts to each individual coil to determine which coil wire goes to which cylinder. There's a pinout chart in the Bentley. Put the multimeter on the dash inside the windsheild - it should be able to reach the DME and the coils if you have reasonably long leads.

This worked like a champ in determining which one of my wires were which, since they weren't marked from the previous owner of the engine that I swapped in.

[VANOS714]

anyone get the $100?

[CreamBeam]

I agree with AlphaE this does sound like it could be related to an extremly plugged up exhaust or damage to an exhaust component like the valves,cat,etc. good luck

[kwill22]

I say timing. Check crank TDC mark and the Cams TDC and make sure they're right. If not Lock flywheel in place and do the timing yourself to make sure. The crank can be easily rotated 180 and the car will still run but will not be happy.

[broach328]

did you ever reach a verdict?